2022
Zeuner, Franziska; Gisler, Daniel; Bianda, Michele; Ramelli, Renzo; Berdyugina, Svetlana V.
In: Evans, Christopher J.; Bryant, Julia J.; Motohara, Kentaro (Ed.): Ground-based and Airborne Instrumentation for Astronomy IX, pp. 121840T, International Society for Optics and Photonics SPIE, 2022.
@inproceedings{10.1117/12.2629250,
title = {Enhancing the accuracy of solar polarimetry by coalescing slow and fast modulation: method description and first performance tests},
author = {Franziska Zeuner and Daniel Gisler and Michele Bianda and Renzo Ramelli and Svetlana V. Berdyugina},
editor = {Christopher J. Evans and Julia J. Bryant and Kentaro Motohara},
url = {http://www.irsol.usi.ch/wp-content/uploads/2022/09/zeuner-etal-spie22.pdf
https://doi.org/10.1117/12.2629250
},
doi = {10.1117/12.2629250},
year = {2022},
date = {2022-08-29},
urldate = {2022-08-29},
booktitle = {Ground-based and Airborne Instrumentation for Astronomy IX},
volume = {12184},
pages = {121840T},
publisher = {SPIE},
organization = {International Society for Optics and Photonics},
abstract = {The polarimetric zero-level accuracy of spectropolarimetric measurements with ground-based solar telescopes usually suffers from systematic telescopic and instrumental effects which are difficult to model, and therefore, cannot be easily removed during post-measurement data reduction. Here, a novel measurement method to enhance the zero-level accuracy to an unprecedented level of such compromised measurements is presented. The method is comprised of adding a slow polarization modulation (< 1 Hz) before any polarizing component of the telescope to a high-sensitivity polarimeter with fast modulation (> 1 kHz). This additional slow modulation significantly mitigates systematic instrumental polarization signals induced by the telescope and post-focus instruments such as polarimetric offsets or cross-talk between polarization states. We present the results and limitations learned from implementing the method at the 45 cm Gregory-Coudé telescope at IRSOL, Locarno. The slow modulation is performed with a low-cost zero-order retarder film mounted in front of the telescope and is combined with the fast modulating Z¨urich IMaging POLarimeter (ZIMPOL). We find that the ground zero of polarization normalized to the intensity is determined within a few 10^{−5 }. This level is consistently achieved over a wide wavelength range in the visible. An improvement of up to a few orders of magnitude for cases where the polarization offset induced by the telescope is as high as 10^{−2} is achieved. This measurement technique allows for enhancing the zero-level accuracy of solar polarimetry, which is crucial for scattering polarization measurements and their theoretical interpretations.},
keywords = {},
pubstate = {published},
tppubtype = {inproceedings}
}
The polarimetric zero-level accuracy of spectropolarimetric measurements with ground-based solar telescopes usually suffers from systematic telescopic and instrumental effects which are difficult to model, and therefore, cannot be easily removed during post-measurement data reduction. Here, a novel measurement method to enhance the zero-level accuracy to an unprecedented level of such compromised measurements is presented. The method is comprised of adding a slow polarization modulation (< 1 Hz) before any polarizing component of the telescope to a high-sensitivity polarimeter with fast modulation (> 1 kHz). This additional slow modulation significantly mitigates systematic instrumental polarization signals induced by the telescope and post-focus instruments such as polarimetric offsets or cross-talk between polarization states. We present the results and limitations learned from implementing the method at the 45 cm Gregory-Coudé telescope at IRSOL, Locarno. The slow modulation is performed with a low-cost zero-order retarder film mounted in front of the telescope and is combined with the fast modulating Z¨urich IMaging POLarimeter (ZIMPOL). We find that the ground zero of polarization normalized to the intensity is determined within a few 10−5 . This level is consistently achieved over a wide wavelength range in the visible. An improvement of up to a few orders of magnitude for cases where the polarization offset induced by the telescope is as high as 10−2 is achieved. This measurement technique allows for enhancing the zero-level accuracy of solar polarimetry, which is crucial for scattering polarization measurements and their theoretical interpretations.
2021
McKenzie, D.; Ishikawa, R.; J., Trujillo Bueno; Auchere, F.; Aleman, T. Pino; Okamoto, T.; Kano, R.; Song, D.; Yoshida, M.; Rachmeler, L.; Kobayashi, K.; Narukage, N.; Kubo, M.; Ishikawa, S.; Hara, H.; Suematsu, Y.; Sakao, T.; Bethge, C.; B., De Pontieu; Vigil, G.; Winebarger, A.; E., Alsina Ballester; Belluzzi, L.; Stepan, J.; A., Asensio Ramos; Carlsson, M.; Leenaarts, J.
Mapping of Solar Magnetic Fields from the Photosphere to the Top of the Chromosphere with CLASP2 Inproceedings
In: American Astronomical Society Meeting Abstracts, pp. 106.03, 2021.
@inproceedings{2021AAS...23810603M,
title = {Mapping of Solar Magnetic Fields from the Photosphere to the Top of the Chromosphere with CLASP2},
author = {D. McKenzie and R. Ishikawa and J., Trujillo Bueno and F. Auchere and T. Pino Aleman and T. Okamoto and R. Kano and D. Song and M. Yoshida and L. Rachmeler and K. Kobayashi and N. Narukage and M. Kubo and S. Ishikawa and H. Hara and Y. Suematsu and T. Sakao and C. Bethge and B., De Pontieu and G. Vigil and A. Winebarger and E., Alsina Ballester and L. Belluzzi and J. Stepan and A., Asensio Ramos and M. Carlsson and J. Leenaarts},
year = {2021},
date = {2021-06-01},
urldate = {2021-06-01},
booktitle = {American Astronomical Society Meeting Abstracts},
volume = {53},
pages = {106.03},
series = {American Astronomical Society Meeting Abstracts},
abstract = {Coronal heating, chromospheric heating, and the heating & acceleration
of the solar wind, are well-known problems in solar physics.
Additionally, knowledge of the magnetic energy that powers solar
flares and coronal mass ejections, important drivers of space
weather, is handicapped by imperfect determination of the
magnetic field in the sun's atmosphere. Extrapolation of
photospheric magnetic measurements into the corona is fraught
with difficulties and uncertainties, partly due to the vastly
different plasma beta between the photosphere and the corona.
Better results in understanding the coronal magnetic field
should be derived from measurements of the magnetic field in the
chromosphere. To that end, we are pursuing quantitative
determination of the magnetic field in the chromosphere, where
plasma beta transitions from greater than unity to less than
unity, via ultraviolet spectropolarimetry. The CLASP2 mission,
flown on a sounding rocket in April 2019, succeeded in measuring
all four Stokes polarization parameters in UV spectral lines
formed by singly ionized Magnesium and neutral Manganese.
Because these ions produce spectral lines under different
conditions, CLASP2 thus was able to quantify the magnetic field
properties at multiple heights in the chromosphere
simultaneously, as shown in the recent paper by Ishikawa et al.
In this presentation we will report the findings of CLASP2,
demonstrating the variation of magnetic fields along a track on
the solar surface and as a function of height in the
chromosphere; and we will illustrate what is next for the CLASP
missions and the demonstration of UV spectropolarimetry in the
solar chromosphere.},
keywords = {},
pubstate = {published},
tppubtype = {inproceedings}
}
Coronal heating, chromospheric heating, and the heating & acceleration
of the solar wind, are well-known problems in solar physics.
Additionally, knowledge of the magnetic energy that powers solar
flares and coronal mass ejections, important drivers of space
weather, is handicapped by imperfect determination of the
magnetic field in the sun's atmosphere. Extrapolation of
photospheric magnetic measurements into the corona is fraught
with difficulties and uncertainties, partly due to the vastly
different plasma beta between the photosphere and the corona.
Better results in understanding the coronal magnetic field
should be derived from measurements of the magnetic field in the
chromosphere. To that end, we are pursuing quantitative
determination of the magnetic field in the chromosphere, where
plasma beta transitions from greater than unity to less than
unity, via ultraviolet spectropolarimetry. The CLASP2 mission,
flown on a sounding rocket in April 2019, succeeded in measuring
all four Stokes polarization parameters in UV spectral lines
formed by singly ionized Magnesium and neutral Manganese.
Because these ions produce spectral lines under different
conditions, CLASP2 thus was able to quantify the magnetic field
properties at multiple heights in the chromosphere
simultaneously, as shown in the recent paper by Ishikawa et al.
In this presentation we will report the findings of CLASP2,
demonstrating the variation of magnetic fields along a track on
the solar surface and as a function of height in the
chromosphere; and we will illustrate what is next for the CLASP
missions and the demonstration of UV spectropolarimetry in the
solar chromosphere.
of the solar wind, are well-known problems in solar physics.
Additionally, knowledge of the magnetic energy that powers solar
flares and coronal mass ejections, important drivers of space
weather, is handicapped by imperfect determination of the
magnetic field in the sun's atmosphere. Extrapolation of
photospheric magnetic measurements into the corona is fraught
with difficulties and uncertainties, partly due to the vastly
different plasma beta between the photosphere and the corona.
Better results in understanding the coronal magnetic field
should be derived from measurements of the magnetic field in the
chromosphere. To that end, we are pursuing quantitative
determination of the magnetic field in the chromosphere, where
plasma beta transitions from greater than unity to less than
unity, via ultraviolet spectropolarimetry. The CLASP2 mission,
flown on a sounding rocket in April 2019, succeeded in measuring
all four Stokes polarization parameters in UV spectral lines
formed by singly ionized Magnesium and neutral Manganese.
Because these ions produce spectral lines under different
conditions, CLASP2 thus was able to quantify the magnetic field
properties at multiple heights in the chromosphere
simultaneously, as shown in the recent paper by Ishikawa et al.
In this presentation we will report the findings of CLASP2,
demonstrating the variation of magnetic fields along a track on
the solar surface and as a function of height in the
chromosphere; and we will illustrate what is next for the CLASP
missions and the demonstration of UV spectropolarimetry in the
solar chromosphere.
Keys, P H; Steiner, O; Vigeesh, G
On the effect of oscillatory phenomena on Stokes inversion results Journal Article
In: Philosophical Transactions of the Royal Society of London Series A, vol. 379, no. 2190, pp. 20200182, 2021.
@article{2021RSPTA.37900182K,
title = {On the effect of oscillatory phenomena on Stokes inversion results},
author = {P H {Keys} and O {Steiner} and G {Vigeesh}},
url = {https://arxiv.org/abs/2008.05539},
doi = {10.1098/rsta.2020.0182},
year = {2021},
date = {2021-02-01},
journal = {Philosophical Transactions of the Royal Society of London Series A},
volume = {379},
number = {2190},
pages = {20200182},
abstract = {Stokes inversion codes are crucial in returning properties of the solar
atmosphere, such as temperature and magnetic field strength.
However, the success of such algorithms to return reliable
values can be hindered by the presence of oscillatory phenomena
within magnetic wave guides. Returning accurate parameters is
crucial to both magnetohydrodynamics (MHD) studies and solar
physics in general. Here, we employ a simulation featuring
propagating MHD waves within a flux tube with a known driver and
atmospheric parameters. We invert the Stokes profiles for the
6301 Å and 6302 Å line pair emergent from the
simulations using the well-known Stokes Inversions from Response
functions code to see if the atmospheric parameters can be
returned for typical spatial resolutions at ground-based
observatories. The inversions return synthetic spectra
comparable to the original input spectra, even with asymmetries
introduced in the spectra from wave propagation in the
atmosphere. The output models from the inversions match closely
to the simulations in temperature, line-of-sight magnetic field
and line-of-sight velocity within typical formation heights of
the inverted lines. Deviations from the simulations are seen
away from these height regions. The inversions results are less
accurate during passage of the waves within the line formation
region. The original wave period could be recovered from the
atmosphere output by the inversions, with empirical mode
decomposition performing better than the wavelet approach in
this task. textbackslashtextbackslashThis article is part of
the Theo Murphy meeting issue `High-resolution wave dynamics in
the lower solar atmosphere'.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Stokes inversion codes are crucial in returning properties of the solar
atmosphere, such as temperature and magnetic field strength.
However, the success of such algorithms to return reliable
values can be hindered by the presence of oscillatory phenomena
within magnetic wave guides. Returning accurate parameters is
crucial to both magnetohydrodynamics (MHD) studies and solar
physics in general. Here, we employ a simulation featuring
propagating MHD waves within a flux tube with a known driver and
atmospheric parameters. We invert the Stokes profiles for the
6301 Å and 6302 Å line pair emergent from the
simulations using the well-known Stokes Inversions from Response
functions code to see if the atmospheric parameters can be
returned for typical spatial resolutions at ground-based
observatories. The inversions return synthetic spectra
comparable to the original input spectra, even with asymmetries
introduced in the spectra from wave propagation in the
atmosphere. The output models from the inversions match closely
to the simulations in temperature, line-of-sight magnetic field
and line-of-sight velocity within typical formation heights of
the inverted lines. Deviations from the simulations are seen
away from these height regions. The inversions results are less
accurate during passage of the waves within the line formation
region. The original wave period could be recovered from the
atmosphere output by the inversions, with empirical mode
decomposition performing better than the wavelet approach in
this task. textbackslashtextbackslashThis article is part of
the Theo Murphy meeting issue `High-resolution wave dynamics in
the lower solar atmosphere'.
atmosphere, such as temperature and magnetic field strength.
However, the success of such algorithms to return reliable
values can be hindered by the presence of oscillatory phenomena
within magnetic wave guides. Returning accurate parameters is
crucial to both magnetohydrodynamics (MHD) studies and solar
physics in general. Here, we employ a simulation featuring
propagating MHD waves within a flux tube with a known driver and
atmospheric parameters. We invert the Stokes profiles for the
6301 Å and 6302 Å line pair emergent from the
simulations using the well-known Stokes Inversions from Response
functions code to see if the atmospheric parameters can be
returned for typical spatial resolutions at ground-based
observatories. The inversions return synthetic spectra
comparable to the original input spectra, even with asymmetries
introduced in the spectra from wave propagation in the
atmosphere. The output models from the inversions match closely
to the simulations in temperature, line-of-sight magnetic field
and line-of-sight velocity within typical formation heights of
the inverted lines. Deviations from the simulations are seen
away from these height regions. The inversions results are less
accurate during passage of the waves within the line formation
region. The original wave period could be recovered from the
atmosphere output by the inversions, with empirical mode
decomposition performing better than the wavelet approach in
this task. textbackslashtextbackslashThis article is part of
the Theo Murphy meeting issue `High-resolution wave dynamics in
the lower solar atmosphere'.
Fleck, B; Carlsson, M; Khomenko, E; Rempel, M; Steiner, O; Vigeesh, G
Acoustic-gravity wave propagation characteristics in three-dimensional radiation hydrodynamic simulations of the solar atmosphere Journal Article
In: Philosophical Transactions of the Royal Society of London Series A, vol. 379, no. 2190, pp. 20200170, 2021.
@article{2021RSPTA.37900170F,
title = {Acoustic-gravity wave propagation characteristics in three-dimensional radiation hydrodynamic simulations of the solar atmosphere},
author = {B {Fleck} and M {Carlsson} and E {Khomenko} and M {Rempel} and O {Steiner} and G {Vigeesh}},
url = {https://arxiv.org/abs/2007.05847},
doi = {10.1098/rsta.2020.0170},
year = {2021},
date = {2021-02-01},
journal = {Philosophical Transactions of the Royal Society of London Series A},
volume = {379},
number = {2190},
pages = {20200170},
abstract = {There has been tremendous progress in the degree of realism of three-
dimensional radiation magneto-hydrodynamic simulations of the
solar atmosphere in the past decades. Four of the most
frequently used numerical codes are Bifrost, CO5BOLD, MANCHA3D
and MURaM. Here we test and compare the wave propagation
characteristics in model runs from these four codes by measuring
the dispersion relation of acoustic-gravity waves at various
heights. We find considerable differences between the various
models. The height dependence of wave power, in particular of
high-frequency waves, varies by up to two orders of magnitude
between the models, and the phase difference spectra of several
models show unexpected features, including
ensuremathpm180textdegree phase jumps.
textbackslashtextbackslashThis article is part of the Theo
Murphy meeting issue `High-resolution wave dynamics in the lower
solar atmosphere'.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
There has been tremendous progress in the degree of realism of three-
dimensional radiation magneto-hydrodynamic simulations of the
solar atmosphere in the past decades. Four of the most
frequently used numerical codes are Bifrost, CO5BOLD, MANCHA3D
and MURaM. Here we test and compare the wave propagation
characteristics in model runs from these four codes by measuring
the dispersion relation of acoustic-gravity waves at various
heights. We find considerable differences between the various
models. The height dependence of wave power, in particular of
high-frequency waves, varies by up to two orders of magnitude
between the models, and the phase difference spectra of several
models show unexpected features, including
ensuremathpm180textdegree phase jumps.
textbackslashtextbackslashThis article is part of the Theo
Murphy meeting issue `High-resolution wave dynamics in the lower
solar atmosphere'.
dimensional radiation magneto-hydrodynamic simulations of the
solar atmosphere in the past decades. Four of the most
frequently used numerical codes are Bifrost, CO5BOLD, MANCHA3D
and MURaM. Here we test and compare the wave propagation
characteristics in model runs from these four codes by measuring
the dispersion relation of acoustic-gravity waves at various
heights. We find considerable differences between the various
models. The height dependence of wave power, in particular of
high-frequency waves, varies by up to two orders of magnitude
between the models, and the phase difference spectra of several
models show unexpected features, including
ensuremathpm180textdegree phase jumps.
textbackslashtextbackslashThis article is part of the Theo
Murphy meeting issue `High-resolution wave dynamics in the lower
solar atmosphere'.
Vigeesh, G; Roth, M; Steiner, O; Fleck, B
On the influence of magnetic topology on the propagation of internal gravity waves in the solar atmosphere Journal Article
In: Philosophical Transactions of the Royal Society of London Series A, vol. 379, no. 2190, pp. 20200177, 2021.
@article{2021RSPTA.37900177V,
title = {On the influence of magnetic topology on the propagation of internal gravity waves in the solar atmosphere},
author = {G {Vigeesh} and M {Roth} and O {Steiner} and B {Fleck}},
url = {https://arxiv.org/abs/2010.06926},
doi = {10.1098/rsta.2020.0177},
year = {2021},
date = {2021-02-01},
journal = {Philosophical Transactions of the Royal Society of London Series A},
volume = {379},
number = {2190},
pages = {20200177},
abstract = {The solar surface is a continuous source of internal gravity waves
(IGWs). IGWs are believed to supply the bulk of the wave energy
for the lower solar atmosphere, but their existence and role for
the energy balance of the upper layers is still unclear, largely
due to the lack of knowledge about the influence of the Sun's
magnetic fields on their propagation. In this work, we look at
naturally excited IGWs in realistic models of the solar
atmosphere and study the effect of different magnetic field
topographies on their propagation. We carry out radiation-
magnetohydrodynamic simulations of a magnetic field free and two
magnetic models-one with an initial, homogeneous, vertical field
of 100 G magnetic flux density and one with an initial
horizontal field of 100 G flux density. The propagation
properties of IGWs are studied by examining the phase-difference
and coherence spectra in the k$_ħ$ - ensuremathømega
diagnostic diagram. We find that IGWs in the upper solar
atmosphere show upward propagation in the model with
predominantly horizontal field similar to the model without
magnetic field. In contrast to that the model with predominantly
vertical fields show downward propagation. This crucial
difference in the propagation direction is also revealed in the
difference in energy transported by waves for heights below 0.8
Mm. Higher up, the propagation properties show a peculiar
behaviour, which require further study. Our analysis suggests
that IGWs may play a significant role in the heating of the
chromospheric layers of the internetwork region where horizontal
fields are thought to be prevalent.
textbackslashtextbackslashThis article is part of the Theo
Murphy meeting issue `High-resolution wave dynamics in the lower
solar atmosphere'.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
The solar surface is a continuous source of internal gravity waves
(IGWs). IGWs are believed to supply the bulk of the wave energy
for the lower solar atmosphere, but their existence and role for
the energy balance of the upper layers is still unclear, largely
due to the lack of knowledge about the influence of the Sun's
magnetic fields on their propagation. In this work, we look at
naturally excited IGWs in realistic models of the solar
atmosphere and study the effect of different magnetic field
topographies on their propagation. We carry out radiation-
magnetohydrodynamic simulations of a magnetic field free and two
magnetic models-one with an initial, homogeneous, vertical field
of 100 G magnetic flux density and one with an initial
horizontal field of 100 G flux density. The propagation
properties of IGWs are studied by examining the phase-difference
and coherence spectra in the k$_ħ$ - ensuremathømega
diagnostic diagram. We find that IGWs in the upper solar
atmosphere show upward propagation in the model with
predominantly horizontal field similar to the model without
magnetic field. In contrast to that the model with predominantly
vertical fields show downward propagation. This crucial
difference in the propagation direction is also revealed in the
difference in energy transported by waves for heights below 0.8
Mm. Higher up, the propagation properties show a peculiar
behaviour, which require further study. Our analysis suggests
that IGWs may play a significant role in the heating of the
chromospheric layers of the internetwork region where horizontal
fields are thought to be prevalent.
textbackslashtextbackslashThis article is part of the Theo
Murphy meeting issue `High-resolution wave dynamics in the lower
solar atmosphere'.
(IGWs). IGWs are believed to supply the bulk of the wave energy
for the lower solar atmosphere, but their existence and role for
the energy balance of the upper layers is still unclear, largely
due to the lack of knowledge about the influence of the Sun's
magnetic fields on their propagation. In this work, we look at
naturally excited IGWs in realistic models of the solar
atmosphere and study the effect of different magnetic field
topographies on their propagation. We carry out radiation-
magnetohydrodynamic simulations of a magnetic field free and two
magnetic models-one with an initial, homogeneous, vertical field
of 100 G magnetic flux density and one with an initial
horizontal field of 100 G flux density. The propagation
properties of IGWs are studied by examining the phase-difference
and coherence spectra in the k$_ħ$ - ensuremathømega
diagnostic diagram. We find that IGWs in the upper solar
atmosphere show upward propagation in the model with
predominantly horizontal field similar to the model without
magnetic field. In contrast to that the model with predominantly
vertical fields show downward propagation. This crucial
difference in the propagation direction is also revealed in the
difference in energy transported by waves for heights below 0.8
Mm. Higher up, the propagation properties show a peculiar
behaviour, which require further study. Our analysis suggests
that IGWs may play a significant role in the heating of the
chromospheric layers of the internetwork region where horizontal
fields are thought to be prevalent.
textbackslashtextbackslashThis article is part of the Theo
Murphy meeting issue `High-resolution wave dynamics in the lower
solar atmosphere'.
2019
B. Joshi K. Upadhyay, P. K. Mitra; Monstein, C.
Solar Radio Observation Using CALLISTO at the USO/PRL, Udaipur Inproceedings
In: 2019 IEEE MTT-S International Microwave and RF Conference (IMARC), pp. 1-6, 2019.
@inproceedings{9118669,
title = {Solar Radio Observation Using CALLISTO at the USO/PRL, Udaipur},
author = {K. Upadhyay, B. Joshi, P. K. Mitra, R. Bhattacharyya, D. Oberoi and C. Monstein},
url = {http://arxiv.org/abs/2007.01655},
doi = {10.1109/IMaRC45935.2019.9118669},
year = {2019},
date = {2019-12-01},
booktitle = {2019 IEEE MTT-S International Microwave and RF Conference (IMARC)},
pages = {1-6},
abstract = {This paper presents a detailed description of various subsystems of CALLISTO solar radio spectrograph installed at the USO/PRL. In the front-end system, a log periodic dipole antenna (LPDA) is designed for the frequency range of 40-900 MHz. In this paper LPDA design, its modifications, and simulation results are presented. We also present some initial observations taken by CALLISTO at Udaipur.},
keywords = {},
pubstate = {published},
tppubtype = {inproceedings}
}
This paper presents a detailed description of various subsystems of CALLISTO solar radio spectrograph installed at the USO/PRL. In the front-end system, a log periodic dipole antenna (LPDA) is designed for the frequency range of 40-900 MHz. In this paper LPDA design, its modifications, and simulation results are presented. We also present some initial observations taken by CALLISTO at Udaipur.
Sampoorna, M.; Nagendra, K. N.; Sowmya, K.; Stenflo, J. O.; Anusha, L. S.
Polarized Line Formation with Incomplete Paschen-Back Effect and Partial Frequency Redistribution Inproceedings
In: Werner, K; Stehle, C; Rauch, T; Lanz, T (Ed.): Astronomical Society of the Pacific Conference Series, pp. 113, 2019.
@inproceedings{2019ASPC..519..113S,
title = {Polarized Line Formation with Incomplete Paschen-Back Effect and Partial Frequency Redistribution},
author = {M. {Sampoorna} and K.N. {Nagendra} and K. {Sowmya} and J.O. {Stenflo} and L.S. {Anusha}},
editor = {K {Werner} and C {Stehle} and T {Rauch} and T {Lanz}},
year = {2019},
date = {2019-07-01},
booktitle = {Astronomical Society of the Pacific Conference Series},
volume = {519},
pages = {113},
series = {Astronomical Society of the Pacific Conference Series},
abstract = {Quantum interference between the hyperfine structure states is known to
depolarize the cores of some of the lines in the linearly
polarized spectrum of the Sun (the Second Solar Spectrum). The
presence of external magnetic fields in the line forming regions
modify these signatures through the Hanle, Zeeman, and
incomplete/ complete Paschen-Back effects (PBE), depending on
the strength of the magnetic field. In an earlier paper, Sowmya
et al. (2014) derived the relevant collisionless partial
frequency redistribution (PFR) matrix for scattering on a two-
level atom with hyperfine structure splitting (HFS) and in the
presence of arbitrary strength magnetic fields (including the
PBE regime). In the present paper we solve the problem of
polarized line transfer in a magnetized atmosphere, including
this PFR matrix. For this purpose, we apply a scattering
expansion method which is based on orders of scattering
approach. We present the results on the combined effects of PBE
and PFR on the polarized line profiles using the atomic
parameters relevant to the Na I D$_2$ line.},
keywords = {},
pubstate = {published},
tppubtype = {inproceedings}
}
Quantum interference between the hyperfine structure states is known to
depolarize the cores of some of the lines in the linearly
polarized spectrum of the Sun (the Second Solar Spectrum). The
presence of external magnetic fields in the line forming regions
modify these signatures through the Hanle, Zeeman, and
incomplete/ complete Paschen-Back effects (PBE), depending on
the strength of the magnetic field. In an earlier paper, Sowmya
et al. (2014) derived the relevant collisionless partial
frequency redistribution (PFR) matrix for scattering on a two-
level atom with hyperfine structure splitting (HFS) and in the
presence of arbitrary strength magnetic fields (including the
PBE regime). In the present paper we solve the problem of
polarized line transfer in a magnetized atmosphere, including
this PFR matrix. For this purpose, we apply a scattering
expansion method which is based on orders of scattering
approach. We present the results on the combined effects of PBE
and PFR on the polarized line profiles using the atomic
parameters relevant to the Na I D$_2$ line.
depolarize the cores of some of the lines in the linearly
polarized spectrum of the Sun (the Second Solar Spectrum). The
presence of external magnetic fields in the line forming regions
modify these signatures through the Hanle, Zeeman, and
incomplete/ complete Paschen-Back effects (PBE), depending on
the strength of the magnetic field. In an earlier paper, Sowmya
et al. (2014) derived the relevant collisionless partial
frequency redistribution (PFR) matrix for scattering on a two-
level atom with hyperfine structure splitting (HFS) and in the
presence of arbitrary strength magnetic fields (including the
PBE regime). In the present paper we solve the problem of
polarized line transfer in a magnetized atmosphere, including
this PFR matrix. For this purpose, we apply a scattering
expansion method which is based on orders of scattering
approach. We present the results on the combined effects of PBE
and PFR on the polarized line profiles using the atomic
parameters relevant to the Na I D$_2$ line.
Sampoorna, M.; Nagendra, K. N.; Frisch, H.; Stenflo, J. O.
Effects of Angle-Dependent Partial Frequency Redistribution on Polarized Line Profiles Inproceedings
In: Werner, K; Stehle, C; Rauch, T; Lanz, T (Ed.): Astronomical Society of the Pacific Conference Series, pp. 109, 2019.
@inproceedings{2019ASPC..519..109S,
title = {Effects of Angle-Dependent Partial Frequency Redistribution on Polarized Line Profiles},
author = {M. {Sampoorna} and K.N. {Nagendra} and H. {Frisch} and J.O. {Stenflo}},
editor = {K {Werner} and C {Stehle} and T {Rauch} and T {Lanz}},
year = {2019},
date = {2019-07-01},
booktitle = {Astronomical Society of the Pacific Conference Series},
volume = {519},
pages = {109},
series = {Astronomical Society of the Pacific Conference Series},
abstract = {Scattering of the solar limb-darkened radiation field on atoms and
molecules produces linearly polarized spectrum of the Sun
(Second Solar Spectrum). Partial frequency redistribution (PFR)
plays a fundamental role in shaping the wings of linearly
polarized profiles of strong resonance lines. Here we present
the effects of the angle-dependent (AD) PFR on resonance
polarization both in the presence and absence of magnetic
fields. We consider scattering on a two-level atom with
unpolarized lower level, and a one-dimensional isothermal
atmosphere.},
keywords = {},
pubstate = {published},
tppubtype = {inproceedings}
}
Scattering of the solar limb-darkened radiation field on atoms and
molecules produces linearly polarized spectrum of the Sun
(Second Solar Spectrum). Partial frequency redistribution (PFR)
plays a fundamental role in shaping the wings of linearly
polarized profiles of strong resonance lines. Here we present
the effects of the angle-dependent (AD) PFR on resonance
polarization both in the presence and absence of magnetic
fields. We consider scattering on a two-level atom with
unpolarized lower level, and a one-dimensional isothermal
atmosphere.
molecules produces linearly polarized spectrum of the Sun
(Second Solar Spectrum). Partial frequency redistribution (PFR)
plays a fundamental role in shaping the wings of linearly
polarized profiles of strong resonance lines. Here we present
the effects of the angle-dependent (AD) PFR on resonance
polarization both in the presence and absence of magnetic
fields. We consider scattering on a two-level atom with
unpolarized lower level, and a one-dimensional isothermal
atmosphere.
Ramelli, R; Bianda, M; Berdyugina, S; Belluzzi, L; Kleint, L
Measurement of the Evolution of the Magnetic Field of the Quiet Photosphere over a Solar Cycle Inproceedings
In: Belluzzi, L; Casini, R; Romoli, M; Bueno, J Trujillo (Ed.): Astronomical Society of the Pacific Conference Series, pp. 283, 2019.
@inproceedings{2019ASPC..526..283R,
title = {Measurement of the Evolution of the Magnetic Field of the Quiet Photosphere over a Solar Cycle},
author = {R {Ramelli} and M {Bianda} and S {Berdyugina} and L {Belluzzi} and L {Kleint}},
editor = {L {Belluzzi} and R {Casini} and M {Romoli} and J {Trujillo Bueno}},
url = {http://aspbooks.org/custom/publications/paper/526-0283.html},
year = {2019},
date = {2019-05-01},
booktitle = {Astronomical Society of the Pacific Conference Series},
volume = {526},
pages = {283},
series = {Astronomical Society of the Pacific Conference Series},
abstract = {The solar photosphere is filled by magnetic fields tangled at scales much smaller than the resolution capability of solar telescopes. These hidden magnetic fields can be investigated via the Hanle effect. In 2007, we started a synoptic program to explore whether the magnetic flux of the quiet photosphere varies with the solar cycle. For this purpose we applied a differential Hanle effect technique based on observations of scattering polarization in C2 molecular lines around 514.0 nm, taken with a cadence of approximately one month. Our results now span almost one complete solar cycle.},
keywords = {},
pubstate = {published},
tppubtype = {inproceedings}
}
The solar photosphere is filled by magnetic fields tangled at scales much smaller than the resolution capability of solar telescopes. These hidden magnetic fields can be investigated via the Hanle effect. In 2007, we started a synoptic program to explore whether the magnetic flux of the quiet photosphere varies with the solar cycle. For this purpose we applied a differential Hanle effect technique based on observations of scattering polarization in C2 molecular lines around 514.0 nm, taken with a cadence of approximately one month. Our results now span almost one complete solar cycle.
Bianda, M; Ramelli, R; Gisler, D; Belluzzi, L; Carlin, E S
Second Solar Spectrum Observations with ZIMPOL Inproceedings
In: Belluzzi, L; Casini, R; Romoli, M; Bueno, J Trujillo (Ed.): Astronomical Society of the Pacific Conference Series, pp. 223, 2019.
@inproceedings{2019ASPC..526..223B,
title = {Second Solar Spectrum Observations with ZIMPOL},
author = {M {Bianda} and R {Ramelli} and D {Gisler} and L {Belluzzi} and E ~S {Carlin}},
editor = {L {Belluzzi} and R {Casini} and M {Romoli} and J {Trujillo Bueno}},
url = {http://aspbooks.org/custom/publications/paper/526-0223.html},
year = {2019},
date = {2019-05-01},
booktitle = {Astronomical Society of the Pacific Conference Series},
volume = {526},
pages = {223},
series = {Astronomical Society of the Pacific Conference Series},
abstract = {The observational activity of IRSOL takes advantage of the high-precision instrumentation available, and of the possibility to carry out programs requiring observing time spread over weeks or months. Particular attention is paid to scattering polarization signals modified by the Hanle effect in spectral lines. Several programs at IRSOL are also aimed at getting the technical know-how necessary to exploit the potentialities of the new generation of large-aperture solar telescopes, which will provide observations with unprecedented spatial and temporal resolution without sacrificing spectropolarimetric sensitivity. In this contribution, we provide a brief description of some projects that are presently carried out at IRSOL.
},
keywords = {},
pubstate = {published},
tppubtype = {inproceedings}
}
The observational activity of IRSOL takes advantage of the high-precision instrumentation available, and of the possibility to carry out programs requiring observing time spread over weeks or months. Particular attention is paid to scattering polarization signals modified by the Hanle effect in spectral lines. Several programs at IRSOL are also aimed at getting the technical know-how necessary to exploit the potentialities of the new generation of large-aperture solar telescopes, which will provide observations with unprecedented spatial and temporal resolution without sacrificing spectropolarimetric sensitivity. In this contribution, we provide a brief description of some projects that are presently carried out at IRSOL.
Ramelli, R; Bianda, M; Setzer, M; Enegelhard, M; Paglia, F; Stenflo, J O; Küveler, G; Plewe, R
Atlas of the Solar Intensity Spectrum and its Center-to-Limb Variation Inproceedings
In: Belluzzi, L; Casini, R; Romoli, M; Bueno, J Trujillo (Ed.): Astronomical Society of the Pacific Conference Series, pp. 287, 2019.
@inproceedings{2019ASPC..526..287R,
title = {Atlas of the Solar Intensity Spectrum and its Center-to-Limb Variation},
author = {R {Ramelli} and M {Bianda} and M {Setzer} and M {Enegelhard} and F {Paglia} and J O {Stenflo} and G {Küveler} and R {Plewe}},
editor = {L {Belluzzi} and R {Casini} and M {Romoli} and J {Trujillo Bueno}},
url = {http://aspbooks.org/custom/publications/paper/526-0287.html},
year = {2019},
date = {2019-05-01},
booktitle = {Astronomical Society of the Pacific Conference Series},
volume = {526},
pages = {287},
series = {Astronomical Society of the Pacific Conference Series},
abstract = {The solar limb darkening function is well known and is widely employed in models of the solar atmosphere. However, there has been a lack of systematic spectrally resolved measurements. Therefore we recently decided to start an observing campaign with the Gregory-Coudé Telescope at IRSOL in Locarno in order to produce a spectral atlas obtained at 10 different heliocentric angles θ, chosen so that μ = cos θ covers the interval from 0.1 to 1.0 in step of 0.1. The measurements carried out till now include the spectral range from 439 nm to 666 nm. The collected data provide information about the anisotropy of the emergent radiation field on the solar surface, allowing a better modeling of the Second Solar Spectrum. In addition the data give observational constraints that should be taken into account when modeling the solar atmosphere.},
keywords = {},
pubstate = {published},
tppubtype = {inproceedings}
}
The solar limb darkening function is well known and is widely employed in models of the solar atmosphere. However, there has been a lack of systematic spectrally resolved measurements. Therefore we recently decided to start an observing campaign with the Gregory-Coudé Telescope at IRSOL in Locarno in order to produce a spectral atlas obtained at 10 different heliocentric angles θ, chosen so that μ = cos θ covers the interval from 0.1 to 1.0 in step of 0.1. The measurements carried out till now include the spectral range from 439 nm to 666 nm. The collected data provide information about the anisotropy of the emergent radiation field on the solar surface, allowing a better modeling of the Second Solar Spectrum. In addition the data give observational constraints that should be taken into account when modeling the solar atmosphere.
Ishikawa, R; Bueno, J Trujillo; Uitenbroek, H; Kubo, M; Tsuneta, S; Goto, M; Kano, R; Narukage, N; Bando, T; Katsukawa, Y; Ishikawa, S; Giono, G; Suematsu, Y; Hara, H; Shimizu, T; Sakao, T; Winebarger, A; Kobayashi, K; Cirtain, J; Champey, P; Auch`ere, F; Štěpán, J; Belluzzi, L; Ramos, A Asensio; Sainz, R Manso; Pomtieu, B De; Ichimoto, K; Carlsson, M; Casini, R
Comparison of Scattering Polarization Signals Observed by CLASP: Possible Indication of the Hanle Effect Inproceedings
In: Belluzzi, L; Casini, R; Romoli, M; Bueno, J Trujillo (Ed.): Astronomical Society of the Pacific Conference Series, pp. 305, 2019.
@inproceedings{2019ASPC..526..305I,
title = {Comparison of Scattering Polarization Signals Observed by CLASP: Possible Indication of the Hanle Effect},
author = {R {Ishikawa} and J {Trujillo Bueno} and H {Uitenbroek} and M {Kubo} and S {Tsuneta} and M {Goto} and R {Kano} and N {Narukage} and T {Bando} and Y {Katsukawa} and S {Ishikawa} and G {Giono} and Y {Suematsu} and H {Hara} and T {Shimizu} and T {Sakao} and A {Winebarger} and K {Kobayashi} and J {Cirtain} and P {Champey} and F {Auch{`e}re} and J {{Š}t{ě}pán} and L {Belluzzi} and A {Asensio Ramos} and R {Manso Sainz} and B {De Pomtieu} and K {Ichimoto} and M {Carlsson} and R {Casini}},
editor = {L {Belluzzi} and R {Casini} and M {Romoli} and J {Trujillo Bueno}},
url = {http://aspbooks.org/custom/publications/paper/526-0305.html},
year = {2019},
date = {2019-05-01},
booktitle = {Astronomical Society of the Pacific Conference Series},
volume = {526},
pages = {305},
series = {Astronomical Society of the Pacific Conference Series},
abstract = {The Chromospheric Lyman-Alpha Spectro-Polarimeter (CLASP; Kano et al.
2012; Kobayashi et al. 2012; Kubo et al. 2014) observed, for the
first time, the linear polarization produced by scattering
processes in the hydrogen Lyman-ensuremathalpha (121.57
nm) and Si III (120.56 nm) lines of the solar disk radiation.
The complexity of the observed scattering polarization (i.e.,
conspicuous spatial variations in Q/I and U/I at spatial scales
of 10″–20″ and the absence of center-to- limb
variation at the Lyman-ensuremathalpha center; see Kano et
al. 2017) motivated us to search for possible hints of the
operation of the Hanle effect by comparing: (a) the
Lyman-ensuremathalpha line center signal, for which the
critical field strength (B$_Ħ$) for the onset of the Hanle
effect is 53 G, (b) the Lyman-ensuremathalpha wing, which
is insensitive to the Hanle effect, and (c) the Si III line, whose B$_Ħ$ = 290 G. We focus on four regions with different
total unsigned photospheric magnetic fluxes (estimated from
SDO/HMI observations), and compare the corresponding U/I spatial
variations in the Lyman-ensuremathalpha wing,
Lyman-ensuremathalpha center, and Si III line. The U/I
signal in the Lyman-ensuremathalpha wing shows an
antisymmetric spatial distribution, which is caused by the
presence of a bright structure in all the selected regions,
regardless of the total unsigned photospheric magnetic flux. In
an internetwork region, the Lyman-ensuremathalpha center
shows an antisymmetric spatial variation across the selected
bright structure, but it does not show it in other more
magnetized regions. In the Si III line, the spatial variation of
U/I deviates from the above-mentioned antisymmetric shape as the
total unsigned photospheric magnetic flux increases. We argue
that a plausible explanation of this differential behavior is
the operation of the Hanle effect.
textbackslashtextbackslashThis work, presented in an oral
contribution at this Workshop, has been published on The
Astrophysical Journal (Ishikawa et al. 2017).},
keywords = {},
pubstate = {published},
tppubtype = {inproceedings}
}
The Chromospheric Lyman-Alpha Spectro-Polarimeter (CLASP; Kano et al.
2012; Kobayashi et al. 2012; Kubo et al. 2014) observed, for the
first time, the linear polarization produced by scattering
processes in the hydrogen Lyman-ensuremathalpha (121.57
nm) and Si III (120.56 nm) lines of the solar disk radiation.
The complexity of the observed scattering polarization (i.e.,
conspicuous spatial variations in Q/I and U/I at spatial scales
of 10″–20″ and the absence of center-to- limb
variation at the Lyman-ensuremathalpha center; see Kano et
al. 2017) motivated us to search for possible hints of the
operation of the Hanle effect by comparing: (a) the
Lyman-ensuremathalpha line center signal, for which the
critical field strength (B$_Ħ$) for the onset of the Hanle
effect is 53 G, (b) the Lyman-ensuremathalpha wing, which
is insensitive to the Hanle effect, and (c) the Si III line, whose B$_Ħ$ = 290 G. We focus on four regions with different
total unsigned photospheric magnetic fluxes (estimated from
SDO/HMI observations), and compare the corresponding U/I spatial
variations in the Lyman-ensuremathalpha wing,
Lyman-ensuremathalpha center, and Si III line. The U/I
signal in the Lyman-ensuremathalpha wing shows an
antisymmetric spatial distribution, which is caused by the
presence of a bright structure in all the selected regions,
regardless of the total unsigned photospheric magnetic flux. In
an internetwork region, the Lyman-ensuremathalpha center
shows an antisymmetric spatial variation across the selected
bright structure, but it does not show it in other more
magnetized regions. In the Si III line, the spatial variation of
U/I deviates from the above-mentioned antisymmetric shape as the
total unsigned photospheric magnetic flux increases. We argue
that a plausible explanation of this differential behavior is
the operation of the Hanle effect.
textbackslashtextbackslashThis work, presented in an oral
contribution at this Workshop, has been published on The
Astrophysical Journal (Ishikawa et al. 2017).
2012; Kobayashi et al. 2012; Kubo et al. 2014) observed, for the
first time, the linear polarization produced by scattering
processes in the hydrogen Lyman-ensuremathalpha (121.57
nm) and Si III (120.56 nm) lines of the solar disk radiation.
The complexity of the observed scattering polarization (i.e.,
conspicuous spatial variations in Q/I and U/I at spatial scales
of 10″–20″ and the absence of center-to- limb
variation at the Lyman-ensuremathalpha center; see Kano et
al. 2017) motivated us to search for possible hints of the
operation of the Hanle effect by comparing: (a) the
Lyman-ensuremathalpha line center signal, for which the
critical field strength (B$_Ħ$) for the onset of the Hanle
effect is 53 G, (b) the Lyman-ensuremathalpha wing, which
is insensitive to the Hanle effect, and (c) the Si III line, whose B$_Ħ$ = 290 G. We focus on four regions with different
total unsigned photospheric magnetic fluxes (estimated from
SDO/HMI observations), and compare the corresponding U/I spatial
variations in the Lyman-ensuremathalpha wing,
Lyman-ensuremathalpha center, and Si III line. The U/I
signal in the Lyman-ensuremathalpha wing shows an
antisymmetric spatial distribution, which is caused by the
presence of a bright structure in all the selected regions,
regardless of the total unsigned photospheric magnetic flux. In
an internetwork region, the Lyman-ensuremathalpha center
shows an antisymmetric spatial variation across the selected
bright structure, but it does not show it in other more
magnetized regions. In the Si III line, the spatial variation of
U/I deviates from the above-mentioned antisymmetric shape as the
total unsigned photospheric magnetic flux increases. We argue
that a plausible explanation of this differential behavior is
the operation of the Hanle effect.
textbackslashtextbackslashThis work, presented in an oral
contribution at this Workshop, has been published on The
Astrophysical Journal (Ishikawa et al. 2017).
Janett, G; Steiner, O; Belluzzi, L
Numerical Methods for the Radiative Transfer Equation of Polarized Light Inproceedings
In: Belluzzi, L; Casini, R; Romoli, M; Bueno, J Trujillo (Ed.): Astronomical Society of the Pacific Conference Series, pp. 133, 2019.
@inproceedings{2019ASPC..526..133J,
title = {Numerical Methods for the Radiative Transfer Equation of Polarized Light},
author = {G {Janett} and O {Steiner} and L {Belluzzi}},
editor = {L {Belluzzi} and R {Casini} and M {Romoli} and J {Trujillo Bueno}},
url = {http://aspbooks.org/custom/publications/paper/526-0133.html},
year = {2019},
date = {2019-05-01},
booktitle = {Astronomical Society of the Pacific Conference Series},
volume = {526},
pages = {133},
series = {Astronomical Society of the Pacific Conference Series},
abstract = {The quest of the ``best formal solver'' available is still open and the
lack of a clear comparison between the different numerical
methods proposed by the community does not facilitate a
conclusion. This work presents a reference paradigm for the
characterization of formal solvers, based on the concepts of
order of accuracy, stability and computational cost. This
overview aims to facilitate the comprehension of the advantages
and weaknesses of the already existing formal solvers and of
those yet to come.},
keywords = {},
pubstate = {published},
tppubtype = {inproceedings}
}
The quest of the ``best formal solver'' available is still open and the
lack of a clear comparison between the different numerical
methods proposed by the community does not facilitate a
conclusion. This work presents a reference paradigm for the
characterization of formal solvers, based on the concepts of
order of accuracy, stability and computational cost. This
overview aims to facilitate the comprehension of the advantages
and weaknesses of the already existing formal solvers and of
those yet to come.
lack of a clear comparison between the different numerical
methods proposed by the community does not facilitate a
conclusion. This work presents a reference paradigm for the
characterization of formal solvers, based on the concepts of
order of accuracy, stability and computational cost. This
overview aims to facilitate the comprehension of the advantages
and weaknesses of the already existing formal solvers and of
those yet to come.
Ballester, E Alsina; Belluzzi, L; Bueno, J Trujillo
The Transfer of Resonance Line Polarization with PRD in the General Hanle-Zeeman Regime Inproceedings
In: Belluzzi, L; Casini, R; Romoli, M; Bueno, J Trujillo (Ed.): Astronomical Society of the Pacific Conference Series, pp. 119, 2019.
@inproceedings{2019ASPC..526..119A,
title = {The Transfer of Resonance Line Polarization with PRD in the General Hanle-Zeeman Regime},
author = {E {Alsina Ballester} and L {Belluzzi} and J {Trujillo Bueno}},
editor = {L {Belluzzi} and R {Casini} and M {Romoli} and J {Trujillo Bueno}},
url = {http://aspbooks.org/custom/publications/paper/526-0119.html},
year = {2019},
date = {2019-05-01},
booktitle = {Astronomical Society of the Pacific Conference Series},
volume = {526},
pages = {119},
series = {Astronomical Society of the Pacific Conference Series},
abstract = {We present numerical radiative transfer calculations of the four Stokes
parameters of the radiation emerging from one-dimensional model
atmospheres. In this investigation we account for the impact of
partial frequency redistribution (PRD) in scattering and the
joint action of the Hanle and Zeeman effects. Strong resonance
lines of interest for chromospheric magnetic field diagnostics
have been considered, namely the Ca I line at 4227 Å and
the Mg II k line at 2795 Å. The Stokes profiles of these
lines have been obtained by considering two-level atomic models,
both in the absence and in the presence of magnetic fields. We
draw attention to the fact that the magneto-optical terms of the
transfer equations for Stokes Q and U are responsible for an
interesting and previously unnoticed magnetic sensitivity of
their scattering polarization profiles beyond the Doppler core.
This important discovery contributes to paint a more detailed
picture of the influence of relatively weak magnetic fields on
the observable linear polarization signals of strong
chromospheric lines, highlighting the importance of a PRD
treatment for such lines.},
keywords = {},
pubstate = {published},
tppubtype = {inproceedings}
}
We present numerical radiative transfer calculations of the four Stokes
parameters of the radiation emerging from one-dimensional model
atmospheres. In this investigation we account for the impact of
partial frequency redistribution (PRD) in scattering and the
joint action of the Hanle and Zeeman effects. Strong resonance
lines of interest for chromospheric magnetic field diagnostics
have been considered, namely the Ca I line at 4227 Å and
the Mg II k line at 2795 Å. The Stokes profiles of these
lines have been obtained by considering two-level atomic models,
both in the absence and in the presence of magnetic fields. We
draw attention to the fact that the magneto-optical terms of the
transfer equations for Stokes Q and U are responsible for an
interesting and previously unnoticed magnetic sensitivity of
their scattering polarization profiles beyond the Doppler core.
This important discovery contributes to paint a more detailed
picture of the influence of relatively weak magnetic fields on
the observable linear polarization signals of strong
chromospheric lines, highlighting the importance of a PRD
treatment for such lines.
parameters of the radiation emerging from one-dimensional model
atmospheres. In this investigation we account for the impact of
partial frequency redistribution (PRD) in scattering and the
joint action of the Hanle and Zeeman effects. Strong resonance
lines of interest for chromospheric magnetic field diagnostics
have been considered, namely the Ca I line at 4227 Å and
the Mg II k line at 2795 Å. The Stokes profiles of these
lines have been obtained by considering two-level atomic models,
both in the absence and in the presence of magnetic fields. We
draw attention to the fact that the magneto-optical terms of the
transfer equations for Stokes Q and U are responsible for an
interesting and previously unnoticed magnetic sensitivity of
their scattering polarization profiles beyond the Doppler core.
This important discovery contributes to paint a more detailed
picture of the influence of relatively weak magnetic fields on
the observable linear polarization signals of strong
chromospheric lines, highlighting the importance of a PRD
treatment for such lines.
Degl'Innocenti, E Landi; Belluzzi, L
Relaxation Phenomena Due to Collisions with Neutral Perturbers in Hyperfine Structure Multiplets Inproceedings
In: Belluzzi, L; Casini, R; Romoli, M; Bueno, J Trujillo (Ed.): Astronomical Society of the Pacific Conference Series, pp. 29, 2019.
@inproceedings{2019ASPC..526...29L,
title = {Relaxation Phenomena Due to Collisions with Neutral Perturbers in Hyperfine Structure Multiplets},
author = {E {Landi Degl'Innocenti} and L {Belluzzi}},
editor = {L {Belluzzi} and R {Casini} and M {Romoli} and J {Trujillo Bueno}},
url = {http://aspbooks.org/custom/publications/paper/526-0029.html},
year = {2019},
date = {2019-05-01},
booktitle = {Astronomical Society of the Pacific Conference Series},
volume = {526},
pages = {29},
series = {Astronomical Society of the Pacific Conference Series},
abstract = {A connection is established between the depolarizing rates, due to
collisions with neutral perturbers, of the statistical tensors
of a hyperfine structure multiplet and those of the statistical
tensors of the parent fine structure level. This connection is
described by a simple equation involving a 12-j symbol of the
second kind. An application is performed to derive an analytical
expression for the scattering matrix of a hyperfine structured
two-level atom in the presence of collisions and a magnetic
field. Numerical results are presented.},
keywords = {},
pubstate = {published},
tppubtype = {inproceedings}
}
A connection is established between the depolarizing rates, due to
collisions with neutral perturbers, of the statistical tensors
of a hyperfine structure multiplet and those of the statistical
tensors of the parent fine structure level. This connection is
described by a simple equation involving a 12-j symbol of the
second kind. An application is performed to derive an analytical
expression for the scattering matrix of a hyperfine structured
two-level atom in the presence of collisions and a magnetic
field. Numerical results are presented.
collisions with neutral perturbers, of the statistical tensors
of a hyperfine structure multiplet and those of the statistical
tensors of the parent fine structure level. This connection is
described by a simple equation involving a 12-j symbol of the
second kind. An application is performed to derive an analytical
expression for the scattering matrix of a hyperfine structured
two-level atom in the presence of collisions and a magnetic
field. Numerical results are presented.
McKenzie, D E; Ishikawa, R; Bueno, J Trujillo; Auchére, F; Rachmeler, L A; Kubo, M; Kobayashi, K; Winebarger, A R; Bethge, C W; Narukage, N; Kano, R; Ishikawa, S; de Pontieu, B; Carlsson, M; Yoshida, M; Belluzzi, L; Štěpán, J; del Pino Alemán, T; Ballester, E Alsina; Ramos, A Asensio
CLASP2: The Chromospheric LAyer Spectro-Polarimeter Inproceedings
In: Belluzzi, L; Casini, R; Romoli, M; Bueno, J Trujillo (Ed.): Astronomical Society of the Pacific Conference Series, pp. 361, 2019.
@inproceedings{2019ASPC..526..361M,
title = {CLASP2: The Chromospheric LAyer Spectro-Polarimeter},
author = {D ~E {McKenzie} and R {Ishikawa} and J {Trujillo Bueno} and F {Auchére} and L ~A {Rachmeler} and M {Kubo} and K {Kobayashi} and A ~R {Winebarger} and C ~W {Bethge} and N {Narukage} and R {Kano} and S {Ishikawa} and B {de Pontieu} and M {Carlsson} and M {Yoshida} and L {Belluzzi} and J {{Š}t{ě}pán} and T {del Pino Alemán} and E {Alsina Ballester} and A {Asensio Ramos}},
editor = {L {Belluzzi} and R {Casini} and M {Romoli} and J {Trujillo Bueno}},
url = {http://aspbooks.org/custom/publications/paper/526-0361.html},
year = {2019},
date = {2019-05-01},
booktitle = {Astronomical Society of the Pacific Conference Series},
volume = {526},
pages = {361},
series = {Astronomical Society of the Pacific Conference Series},
abstract = {The hydrogen Lyman-ensuremathalpha line at 121.6 nm and the Mg k
line at 279.5 nm are especially relevant for deciphering the
magnetic structure of the chromosphere since their line-center
signals are formed in the chromosphere and transition region,
with unique sensitivities to magnetic fields. We propose the
Chromospheric LAyer Spectro-Polarimeter (CLASP2), to build upon
the success of the first CLASP flight, which measured the linear
polarization in H I Lyman-ensuremathalpha. The existing
CLASP instrument will be refitted to measure all four Stokes
parameters in the 280 nm range, including variations due to the
anisotropic radiation pumping, the Hanle effect, and the Zeeman
effect.},
keywords = {},
pubstate = {published},
tppubtype = {inproceedings}
}
The hydrogen Lyman-ensuremathalpha line at 121.6 nm and the Mg k
line at 279.5 nm are especially relevant for deciphering the
magnetic structure of the chromosphere since their line-center
signals are formed in the chromosphere and transition region,
with unique sensitivities to magnetic fields. We propose the
Chromospheric LAyer Spectro-Polarimeter (CLASP2), to build upon
the success of the first CLASP flight, which measured the linear
polarization in H I Lyman-ensuremathalpha. The existing
CLASP instrument will be refitted to measure all four Stokes
parameters in the 280 nm range, including variations due to the
anisotropic radiation pumping, the Hanle effect, and the Zeeman
effect.
line at 279.5 nm are especially relevant for deciphering the
magnetic structure of the chromosphere since their line-center
signals are formed in the chromosphere and transition region,
with unique sensitivities to magnetic fields. We propose the
Chromospheric LAyer Spectro-Polarimeter (CLASP2), to build upon
the success of the first CLASP flight, which measured the linear
polarization in H I Lyman-ensuremathalpha. The existing
CLASP instrument will be refitted to measure all four Stokes
parameters in the 280 nm range, including variations due to the
anisotropic radiation pumping, the Hanle effect, and the Zeeman
effect.
Dhara, Sajal Kumar; Capozzi, Emilia; Gisler, Daniel; Bianda, Michele; Ramelli, Renzo; Berdyugina, Svetlana; Alsina, Ernest; Belluzzi, Luca
Spatial variations of the Sr I 4607 Åscattering polarization signals at subgranular scale observed with ZIMPOL at the GREGOR telescope Journal Article
In: Nuovo Cimento C Geophysics Space Physics C, vol. 42, no. 1, pp. 6, 2019.
@article{2019NCimC..42....6K,
title = {Spatial variations of the Sr I 4607 Åscattering polarization signals at subgranular scale observed with ZIMPOL at the GREGOR telescope},
author = {Sajal {Kumar Dhara} and Emilia {Capozzi} and Daniel {Gisler} and Michele {Bianda} and Renzo {Ramelli} and Svetlana {Berdyugina} and Ernest {Alsina} and Luca {Belluzzi}},
url = {https://arxiv.org/abs/1904.03986},
doi = {10.1393/ncc/i2019-19006-1},
year = {2019},
date = {2019-01-01},
journal = {Nuovo Cimento C Geophysics Space Physics C},
volume = {42},
number = {1},
pages = {6},
abstract = {Sr I 4607 Åspectral line shows one of the strongest scattering
polarization signals in the visible solar spectrum. The
amplitudes of these signals are expected to vary at granular
spatial scales. This variation can be due to changes in the
magnetic field intensity and orientation (Hanle effect) as well
as due to spatial and temporal variations in the plasma
properties. Measuring the spatial variation of such polarization
signal are challenging since both high spatial resolution and
high spectropolarimetric sensitivity are required at the same
time. To the aim of measuring these spatial variations at
granular scale, we carried out a spectro-polarimetric
measurement with the Zurich IMaging POLarimeter (ZIMPOL), at the
GREGOR solar telescope at different limb distances on solar
disk. Our results show a spatial variation of scattering linear
polarization signals in Sr I 4607 Åline at the granular
scale at every ensuremathmu, starting from 0.2 to 0.8. The
correlation between the scattering linear polarization signal
amplitude and the continuum intensity imply statistically that
the scattering polarization is higher at the granular regions
than in the intergranular lanes.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Sr I 4607 Åspectral line shows one of the strongest scattering
polarization signals in the visible solar spectrum. The
amplitudes of these signals are expected to vary at granular
spatial scales. This variation can be due to changes in the
magnetic field intensity and orientation (Hanle effect) as well
as due to spatial and temporal variations in the plasma
properties. Measuring the spatial variation of such polarization
signal are challenging since both high spatial resolution and
high spectropolarimetric sensitivity are required at the same
time. To the aim of measuring these spatial variations at
granular scale, we carried out a spectro-polarimetric
measurement with the Zurich IMaging POLarimeter (ZIMPOL), at the
GREGOR solar telescope at different limb distances on solar
disk. Our results show a spatial variation of scattering linear
polarization signals in Sr I 4607 Åline at the granular
scale at every ensuremathmu, starting from 0.2 to 0.8. The
correlation between the scattering linear polarization signal
amplitude and the continuum intensity imply statistically that
the scattering polarization is higher at the granular regions
than in the intergranular lanes.
polarization signals in the visible solar spectrum. The
amplitudes of these signals are expected to vary at granular
spatial scales. This variation can be due to changes in the
magnetic field intensity and orientation (Hanle effect) as well
as due to spatial and temporal variations in the plasma
properties. Measuring the spatial variation of such polarization
signal are challenging since both high spatial resolution and
high spectropolarimetric sensitivity are required at the same
time. To the aim of measuring these spatial variations at
granular scale, we carried out a spectro-polarimetric
measurement with the Zurich IMaging POLarimeter (ZIMPOL), at the
GREGOR solar telescope at different limb distances on solar
disk. Our results show a spatial variation of scattering linear
polarization signals in Sr I 4607 Åline at the granular
scale at every ensuremathmu, starting from 0.2 to 0.8. The
correlation between the scattering linear polarization signal
amplitude and the continuum intensity imply statistically that
the scattering polarization is higher at the granular regions
than in the intergranular lanes.
2018
Ramelli, Renzo; Cagnotti, Marco; Cortesi, Sergio; Bianda, Michele; Manna, Andrea
Sunspot data collection of Specola Solare Ticinese in Locarno Conference Forthcoming
Proceedings IAU Symposium , no. 340, IAU Proceedings Series IAU Publisher, Cambridge University Press , Forthcoming.
@conference{ramelli_iaus340,
title = {Sunspot data collection of Specola Solare Ticinese in Locarno},
author = {Renzo Ramelli and Marco Cagnotti and Sergio Cortesi and Michele Bianda and Andrea Manna},
url = {http://www.irsol.usi.ch/wp-content/uploads/2018/05/ramelli_iaus340.pdf
http://arxiv.org/abs/1805.09202},
year = {2018},
date = {2018-05-23},
booktitle = {Proceedings IAU Symposium },
number = {340},
publisher = {IAU Publisher, Cambridge University Press },
series = {IAU Proceedings Series},
abstract = {Sunspot observations and counting are carried out at the Specola Solare Ticinese in Locarno since 1957 when it was built as an external observing station of the Zurich observatory.
When in 1980 the data center responsibility was transferred from ETH Zurich to the Royal Observatory of Belgium in Brussels, the observations in Locarno continued and Specola Solare Ticinese got the role of pilot station. The data collected at Specola cover now the last 6 solar cycles.
The aim of this presentation is to discuss and give an overview about the Specola data collection, the applied counting method and the future archiving projects. The latter includes the publication of all data and drawings in digital form in collaboration with the ETH Zurich University Archives, where a parallel digitization project is ongoing for the document of the former Swiss Federal Observatory in Zurich collected since the time of Rudolph Wolf.
},
keywords = {},
pubstate = {forthcoming},
tppubtype = {conference}
}
Sunspot observations and counting are carried out at the Specola Solare Ticinese in Locarno since 1957 when it was built as an external observing station of the Zurich observatory.
When in 1980 the data center responsibility was transferred from ETH Zurich to the Royal Observatory of Belgium in Brussels, the observations in Locarno continued and Specola Solare Ticinese got the role of pilot station. The data collected at Specola cover now the last 6 solar cycles.
The aim of this presentation is to discuss and give an overview about the Specola data collection, the applied counting method and the future archiving projects. The latter includes the publication of all data and drawings in digital form in collaboration with the ETH Zurich University Archives, where a parallel digitization project is ongoing for the document of the former Swiss Federal Observatory in Zurich collected since the time of Rudolph Wolf.
When in 1980 the data center responsibility was transferred from ETH Zurich to the Royal Observatory of Belgium in Brussels, the observations in Locarno continued and Specola Solare Ticinese got the role of pilot station. The data collected at Specola cover now the last 6 solar cycles.
The aim of this presentation is to discuss and give an overview about the Specola data collection, the applied counting method and the future archiving projects. The latter includes the publication of all data and drawings in digital form in collaboration with the ETH Zurich University Archives, where a parallel digitization project is ongoing for the document of the former Swiss Federal Observatory in Zurich collected since the time of Rudolph Wolf.
2017
Rachmeler, L; McKenzie, D E; Ishikawa, R; Bueno, J Trujillo; Auchère, F; Kobayashi, K; Winebarger, A; Bethge, C; Kano, R; Kubo, M; Song, D; Narukage, N; Ishikawa, S; Pontieu, B De; Carlsson, M; Yoshida, M; Belluzzi, L; Stepan, J; del Pino Alemná, T; Ballester, E A; Ramos, A Asensio
CLASP2: The Chromospheric LAyer Spectro-Polarimeter Inproceedings
In: AAS/Solar Physics Division Meeting, pp. 110.10, 2017.
@inproceedings{2017SPD....4811010R,
title = {CLASP2: The Chromospheric LAyer Spectro-Polarimeter},
author = {L {Rachmeler} and D {E McKenzie} and R {Ishikawa} and J {Trujillo Bueno} and F {Auchère} and K {Kobayashi} and A {Winebarger} and C {Bethge} and R {Kano} and M {Kubo} and D {Song} and N {Narukage} and S {Ishikawa} and B {De Pontieu} and M {Carlsson} and M {Yoshida} and L {Belluzzi} and J {Stepan} and T {del Pino Alemná} and E A {Ballester} and A {Asensio Ramos}},
url = {http://adsabs.harvard.edu/abs/2017SPD....4811010R},
year = {2017},
date = {2017-08-01},
booktitle = {AAS/Solar Physics Division Meeting},
volume = {48},
pages = {110.10},
series = {AAS/Solar Physics Division Meeting},
abstract = {We present the instrument, science case, and timeline of the CLASP2
sounding rocket mission. The successful CLASP (Chromospheric Lyman-Alpha
Spectro-Polarimeter) sounding rocket flight in 2015 resulted in the
first-ever linear polarization measurements of solar hydrogen
Lyman-alpha line, which is sensitive to the Hanle effect and can be used
to constrain the magnetic field and geometric complexity of the upper
chromosphere. Ly-alpha is one of several upper chromospheric lines that
contain magnetic information. In the spring of 2019, we will re-fly the
modified CLASP telescope to measure the full Stokes profile of Mg II h
amp k near 280 nm. This set of lines is sensitive to the upper
chromospheric magnetic field via both the Hanle and the Zeeman effects. },
keywords = {},
pubstate = {published},
tppubtype = {inproceedings}
}
We present the instrument, science case, and timeline of the CLASP2
sounding rocket mission. The successful CLASP (Chromospheric Lyman-Alpha
Spectro-Polarimeter) sounding rocket flight in 2015 resulted in the
first-ever linear polarization measurements of solar hydrogen
Lyman-alpha line, which is sensitive to the Hanle effect and can be used
to constrain the magnetic field and geometric complexity of the upper
chromosphere. Ly-alpha is one of several upper chromospheric lines that
contain magnetic information. In the spring of 2019, we will re-fly the
modified CLASP telescope to measure the full Stokes profile of Mg II h
amp k near 280 nm. This set of lines is sensitive to the upper
chromospheric magnetic field via both the Hanle and the Zeeman effects.
sounding rocket mission. The successful CLASP (Chromospheric Lyman-Alpha
Spectro-Polarimeter) sounding rocket flight in 2015 resulted in the
first-ever linear polarization measurements of solar hydrogen
Lyman-alpha line, which is sensitive to the Hanle effect and can be used
to constrain the magnetic field and geometric complexity of the upper
chromosphere. Ly-alpha is one of several upper chromospheric lines that
contain magnetic information. In the spring of 2019, we will re-fly the
modified CLASP telescope to measure the full Stokes profile of Mg II h
amp k near 280 nm. This set of lines is sensitive to the upper
chromospheric magnetic field via both the Hanle and the Zeeman effects.
Vigeesh, G; Steiner, O; Calvo, F; Roth, M
On the effect of vorticity on the propagation of internal gravity waves. Inproceedings
In: pp. 54, 2017.
@inproceedings{2017MmSAI..88...54V,
title = {On the effect of vorticity on the propagation of internal gravity waves.},
author = {G {Vigeesh} and O {Steiner} and F {Calvo} and M {Roth}},
year = {2017},
date = {2017-05-01},
journal = {Mem. Societa Astronomica Italiana},
volume = {88},
pages = {54},
abstract = {We compare different models of solar surface convection to study
vorticity and how it can influence the propagation of internal gravity
waves. We conclude that simulations performed with higher grid
resolution may have a reduced gravity wave flux in the lower part of the
atmosphere due to strong vorticity. We also show that the vertical
extent of the allowed region of propagation depends on the magnetic
field inclination. },
keywords = {},
pubstate = {published},
tppubtype = {inproceedings}
}
We compare different models of solar surface convection to study
vorticity and how it can influence the propagation of internal gravity
waves. We conclude that simulations performed with higher grid
resolution may have a reduced gravity wave flux in the lower part of the
atmosphere due to strong vorticity. We also show that the vertical
extent of the allowed region of propagation depends on the magnetic
field inclination.
vorticity and how it can influence the propagation of internal gravity
waves. We conclude that simulations performed with higher grid
resolution may have a reduced gravity wave flux in the lower part of the
atmosphere due to strong vorticity. We also show that the vertical
extent of the allowed region of propagation depends on the magnetic
field inclination.
Steiner, O.; Calvo, F.; Salhab, R.; G.Vigeesh,
CO5BOLD for MHD: progresses and deficiencies . Inproceedings
In: pp. 37, 2017.
@inproceedings{2017MmSAI..88...37S,
title = {CO5BOLD for MHD: progresses and deficiencies .},
author = {O. Steiner and F. Calvo and R. Salhab and G.Vigeesh},
year = {2017},
date = {2017-01-01},
journal = {Mem. Societa Astronomica Italiana},
volume = {88},
pages = {37},
abstract = {The magnetohydrodynamics module of CO5BOLD has been steadily improved
over the past decade and has been used for various solar and stellar
physical applications. We give an overview of current work with it and
of remaining and newly emerged shortcomings. },
keywords = {},
pubstate = {published},
tppubtype = {inproceedings}
}
The magnetohydrodynamics module of CO5BOLD has been steadily improved
over the past decade and has been used for various solar and stellar
physical applications. We give an overview of current work with it and
of remaining and newly emerged shortcomings.
over the past decade and has been used for various solar and stellar
physical applications. We give an overview of current work with it and
of remaining and newly emerged shortcomings.
2016
E. Stellmacher Wiehr, G.; Bianda, M.
The Electron Density in a Quiescent Prominence Inproceedings
In: pp. 79-85, 2016.
@inproceedings{2016CEAB...40...79W,
title = {The Electron Density in a Quiescent Prominence},
author = {Wiehr, E. Stellmacher, G. and Bianda, M.},
year = {2016},
date = {2016-02-01},
journal = {Central European Astrophysical Bulletin},
volume = {40},
pages = {79-85},
keywords = {},
pubstate = {published},
tppubtype = {inproceedings}
}
Stenflo, J. O.
The Sun's spectrally resolved center-to-limb variation Inproceedings
In: AAS/Solar Physics Division Meeting, pp. 12.08, 2016.
@inproceedings{2016SPD....47.1208S,
title = {The Sun's spectrally resolved center-to-limb variation},
author = {Stenflo, J.O.},
year = {2016},
date = {2016-01-01},
booktitle = {AAS/Solar Physics Division Meeting},
volume = {47},
pages = {12.08},
series = {AAS/Solar Physics Division Meeting},
abstract = {The center-to-limb variation (CLV) of the Sun's continuous spectrum is
well known and has served as a major observational constraint on models
of the solar atmosphere. The CLV however also varies dramatically with
wavelength inside each spectral line. Here we report on two new atlases
that show the properties of the CLV with high spectral resolution. One
is a fully resolved spectral atlas from 4084 to 9950 AA of the
ratio between the near limb spectrum, at 10 arcsec inside the limb, and
the disk center spectrum, both recorded with the FTS at NSO/Kitt Peak.
The other atlas gives the same kind of information but covers the whole
range of limb distances by giving the ratio spectra for the nine $mu$
positions 0.1, 0.2, łdots, 0.9. This set of nine atlases for different
$mu$ have been recorded over the last couple of years with the solar
facility at IRSOL (Istituto Ricerche Solari Locarno) in Switzerland. We
find that the CLV is spectrally as richly structured as the ordinary
intensity spectrum, but the structuring is different and contains
diagnostic information that is not contained in the intensity spectrum.
Here we illustrate the properties of the new spectral structures and
discuss what they mean. },
keywords = {},
pubstate = {published},
tppubtype = {inproceedings}
}
The center-to-limb variation (CLV) of the Sun's continuous spectrum is
well known and has served as a major observational constraint on models
of the solar atmosphere. The CLV however also varies dramatically with
wavelength inside each spectral line. Here we report on two new atlases
that show the properties of the CLV with high spectral resolution. One
is a fully resolved spectral atlas from 4084 to 9950 AA of the
ratio between the near limb spectrum, at 10 arcsec inside the limb, and
the disk center spectrum, both recorded with the FTS at NSO/Kitt Peak.
The other atlas gives the same kind of information but covers the whole
range of limb distances by giving the ratio spectra for the nine $mu$
positions 0.1, 0.2, łdots, 0.9. This set of nine atlases for different
$mu$ have been recorded over the last couple of years with the solar
facility at IRSOL (Istituto Ricerche Solari Locarno) in Switzerland. We
find that the CLV is spectrally as richly structured as the ordinary
intensity spectrum, but the structuring is different and contains
diagnostic information that is not contained in the intensity spectrum.
Here we illustrate the properties of the new spectral structures and
discuss what they mean.
well known and has served as a major observational constraint on models
of the solar atmosphere. The CLV however also varies dramatically with
wavelength inside each spectral line. Here we report on two new atlases
that show the properties of the CLV with high spectral resolution. One
is a fully resolved spectral atlas from 4084 to 9950 AA of the
ratio between the near limb spectrum, at 10 arcsec inside the limb, and
the disk center spectrum, both recorded with the FTS at NSO/Kitt Peak.
The other atlas gives the same kind of information but covers the whole
range of limb distances by giving the ratio spectra for the nine $mu$
positions 0.1, 0.2, łdots, 0.9. This set of nine atlases for different
$mu$ have been recorded over the last couple of years with the solar
facility at IRSOL (Istituto Ricerche Solari Locarno) in Switzerland. We
find that the CLV is spectrally as richly structured as the ordinary
intensity spectrum, but the structuring is different and contains
diagnostic information that is not contained in the intensity spectrum.
Here we illustrate the properties of the new spectral structures and
discuss what they mean.
2015
Smitha, H. N.; Nagendra, K. N.; Stenflo, J. O.; Bianda, M.; Sampoorna, M.; Ramelli, R.
A revisit to model the Cr i triplet at 5204-5208 Å and the Ba ii D2 line at 4554 Å in the Second Solar Spectrum Inproceedings
In: Nagendra, K. N.; Bagnulo, S.; Centeno, R.; Martínez González, M. J. (Ed.): Polarimetry, pp. 372-376, 2015.
@inproceedings{2015IAUS..305..372S,
title = {A revisit to model the Cr i triplet at 5204-5208 Å and the Ba ii D2 line at 4554 Å in the Second Solar Spectrum},
author = {Smitha, H.N. and Nagendra, K.N. and Stenflo, J.O. and Bianda, M. and Sampoorna, M. and Ramelli, R.},
editor = {Nagendra, K.N. and Bagnulo, S. and Centeno, R. and Martínez González, M.J.},
url = {http://adsabs.harvard.edu/abs/2015IAUS..305..372S},
doi = {10.1017/S1743921315005074},
year = {2015},
date = {2015-10-01},
urldate = {2015-10-01},
booktitle = {Polarimetry},
volume = {305},
pages = {372-376},
series = {IAU Symposium},
abstract = {In our previous attempt to model the Stokes profiles of the Cr i triplet at 5204-5208 Å and the Ba ii D2 at 4554 Å, we found it necessary to slightly modify the standard FAL model atmospheres to fit the observed polarization profiles. In the case of Cr i triplet, this modification was done to reduce the theoretical continuum polarization, and in the case of Ba ii D2, it was needed to reproduce the central peak in Q/I. In this work, we revisit both these cases using different standard model atmospheres whose temperature structures closely resemble those of the modified FAL models, and explore the possibility of synthesizing the line profiles without the need for small modifications of the model atmosphere.},
keywords = {},
pubstate = {published},
tppubtype = {inproceedings}
}
In our previous attempt to model the Stokes profiles of the Cr i triplet at 5204-5208 Å and the Ba ii D2 at 4554 Å, we found it necessary to slightly modify the standard FAL model atmospheres to fit the observed polarization profiles. In the case of Cr i triplet, this modification was done to reduce the theoretical continuum polarization, and in the case of Ba ii D2, it was needed to reproduce the central peak in Q/I. In this work, we revisit both these cases using different standard model atmospheres whose temperature structures closely resemble those of the modified FAL models, and explore the possibility of synthesizing the line profiles without the need for small modifications of the model atmosphere.
Sowmya, K.; Nagendra, K. N.; Sampoorna, M.; Stenflo, J. O.
Paschen-Back effect involving atomic fine and hyperfine structure states Inproceedings
In: Nagendra, K. N.; Bagnulo, S.; Centeno, R.; Martínez González, M. J. (Ed.): Polarimetry, pp. 154-158, 2015.
@inproceedings{2015IAUS..305..154S,
title = {Paschen-Back effect involving atomic fine and hyperfine structure states},
author = {Sowmya, K. and Nagendra, K.N. and Sampoorna, M. and Stenflo, J.O.},
editor = {Nagendra, K.N. and Bagnulo, S. and Centeno, R. and Martínez González, M.J.},
url = {http://adsabs.harvard.edu/abs/2015IAUS..305..154S},
doi = {10.1017/S1743921315004688},
year = {2015},
date = {2015-10-01},
urldate = {2015-10-01},
booktitle = {Polarimetry},
volume = {305},
pages = {154-158},
series = {IAU Symposium},
abstract = {The linear polarization in spectral lines produced by coherent scattering is significantly modified by the quantum interference between the atomic states in the presence of a magnetic field. When magnetic fields produce a splitting which is of the order of or greater than the fine or hyperfine structure splittings, we enter the Paschen-Back effect (PBE) regime, in which the magnetic field dependence of the Zeeman splittings and transition amplitudes becomes non-linear. In general, PBE occurs for sufficiently strong fields when the fine structure states are involved and for weak fields in the case of hyperfine structure states. In this work, we apply the recently developed theory of PBE in the atomic fine and hyperfine structure states including the effects of partial frequency redistribution to the case of Li i 6708 Å doublet. We explore the signatures of PBE in a single scattering event and their applicability to the solar magnetic field diagnostics.},
keywords = {},
pubstate = {published},
tppubtype = {inproceedings}
}
The linear polarization in spectral lines produced by coherent scattering is significantly modified by the quantum interference between the atomic states in the presence of a magnetic field. When magnetic fields produce a splitting which is of the order of or greater than the fine or hyperfine structure splittings, we enter the Paschen-Back effect (PBE) regime, in which the magnetic field dependence of the Zeeman splittings and transition amplitudes becomes non-linear. In general, PBE occurs for sufficiently strong fields when the fine structure states are involved and for weak fields in the case of hyperfine structure states. In this work, we apply the recently developed theory of PBE in the atomic fine and hyperfine structure states including the effects of partial frequency redistribution to the case of Li i 6708 Å doublet. We explore the signatures of PBE in a single scattering event and their applicability to the solar magnetic field diagnostics.
Carlin, E. S.
Chromospheric diagnosis with forward scattering polarization Inproceedings
In: Nagendra, K. N.; Bagnulo, S.; Centeno, R.; Martínez González, M. J. (Ed.): Polarimetry, pp. 146-153, 2015.
@inproceedings{2015IAUS..305..146C,
title = {Chromospheric diagnosis with forward scattering polarization},
author = {Carlin, E.S.},
editor = {Nagendra, K.N. and Bagnulo, S. and Centeno, R. and Martínez González, M.J.},
url = {http://adsabs.harvard.edu/abs/2015IAUS..305..146C},
doi = {10.1017/S1743921315004676},
year = {2015},
date = {2015-10-01},
urldate = {2015-10-01},
booktitle = {Polarimetry},
volume = {305},
pages = {146-153},
series = {IAU Symposium},
abstract = {Is it physically feasible to perform chromospheric diagnosis using spatial maps of scattering polarization at the solar disk center? To investigate it we synthesized polarization maps (in 8542 Angstroms) resulting from MHD solar models and NLTE radiative transfer calculations that consider Hanle effect and vertical macroscopic motions. After explaining the physical con- text of forward scattering and presenting our results, we arrive at the definition of Hanle polarity inversion lines. We show how such features can give support for a clearer chromospheric diagnosis in which the magnetic and dynamic effects in the scattering polarization could be disentangled},
keywords = {},
pubstate = {published},
tppubtype = {inproceedings}
}
Is it physically feasible to perform chromospheric diagnosis using spatial maps of scattering polarization at the solar disk center? To investigate it we synthesized polarization maps (in 8542 Angstroms) resulting from MHD solar models and NLTE radiative transfer calculations that consider Hanle effect and vertical macroscopic motions. After explaining the physical con- text of forward scattering and presenting our results, we arrive at the definition of Hanle polarity inversion lines. We show how such features can give support for a clearer chromospheric diagnosis in which the magnetic and dynamic effects in the scattering polarization could be disentangled
Stenflo, J. O.
Coherence structure of D1 scattering Inproceedings
In: Nagendra, K. N.; Bagnulo, S.; Centeno, R.; Martínez González, M. J. (Ed.): Polarimetry, pp. 136-145, 2015.
@inproceedings{2015IAUS..305..136S,
title = {Coherence structure of D1 scattering},
author = {Stenflo, J.O.},
editor = {Nagendra, K.N. and Bagnulo, S. and Centeno, R. and Martínez González, M.J.},
url = {http://adsabs.harvard.edu/abs/2015IAUS..305..136S},
doi = {10.1017/S1743921315004664},
year = {2015},
date = {2015-10-01},
urldate = {2015-10-01},
booktitle = {Polarimetry},
volume = {305},
pages = {136-145},
series = {IAU Symposium},
abstract = {The extensive literature on the physics of polarized scattering may give the impression that we have a solid theoretical foundation for the interpretation of spectro-polarimetric data. This theoretical framework has however not been sufficiently tested by experiments under controlled conditions. While the solar atmosphere may be viewed as a physics laboratory, the observed solar polarization depends on too many environmental factors that are beyond our control. The existence of a symmetric polarization peak at the center of the solar Na D1 line has remained an enigma for two decades, in spite of persistent efforts to explain it with available quantum theory. A decade ago a laboratory experiment was set up to determine whether this was a problem for solar physics or quantum physics. The experiment revealed a rich polarization structure of D1 scattering, although available quantum theory predicted null results. It has now finally been possible to formulate a well-defined and self-consistent extension of the theory of quantum scattering that can reproduce in great quantitative detail the main polarization structures that were found in the laboratory experiment. Here we give a brief overview of the new physical ingredients that were missing before. The extended theory reveals that multi-level atomic systems have a far richer coherence structure than previously believed.},
keywords = {},
pubstate = {published},
tppubtype = {inproceedings}
}
The extensive literature on the physics of polarized scattering may give the impression that we have a solid theoretical foundation for the interpretation of spectro-polarimetric data. This theoretical framework has however not been sufficiently tested by experiments under controlled conditions. While the solar atmosphere may be viewed as a physics laboratory, the observed solar polarization depends on too many environmental factors that are beyond our control. The existence of a symmetric polarization peak at the center of the solar Na D1 line has remained an enigma for two decades, in spite of persistent efforts to explain it with available quantum theory. A decade ago a laboratory experiment was set up to determine whether this was a problem for solar physics or quantum physics. The experiment revealed a rich polarization structure of D1 scattering, although available quantum theory predicted null results. It has now finally been possible to formulate a well-defined and self-consistent extension of the theory of quantum scattering that can reproduce in great quantitative detail the main polarization structures that were found in the laboratory experiment. Here we give a brief overview of the new physical ingredients that were missing before. The extended theory reveals that multi-level atomic systems have a far richer coherence structure than previously believed.
Trujillo Bueno, J.; Del Pino Alemán, T.; Belluzzi, L.
Atomic Scattering Polarization. Observations, Modeling, Predictions Inproceedings
In: Nagendra, K. N.; Bagnulo, S.; Centeno, R.; Martínez González, M. J. (Ed.): Polarimetry, pp. 127-135, 2015.
@inproceedings{2015IAUS..305..127T,
title = {Atomic Scattering Polarization. Observations, Modeling, Predictions},
author = {Trujillo Bueno, J. and Del Pino Alemán, T. and Belluzzi, L.},
editor = {Nagendra, K.N. and Bagnulo, S. and Centeno, R. and Martínez González, M.J.},
url = {http://adsabs.harvard.edu/abs/2015IAUS..305..127B},
doi = {10.1017/S1743921315004652},
year = {2015},
date = {2015-10-01},
urldate = {2015-10-01},
booktitle = {Polarimetry},
volume = {305},
pages = {127-135},
series = {IAU Symposium},
abstract = {This paper highlights very recent advances concerning the identification of new mechanisms that introduce polarization in spectral lines, which turn out to be key for understanding some of the most enigmatic scattering polarization signals of the solar visible spectrum. We also show a radiative transfer prediction on the scattering polarization pattern across the Mg ii h & k lines, whose radiation can only be observed from space},
keywords = {},
pubstate = {published},
tppubtype = {inproceedings}
}
This paper highlights very recent advances concerning the identification of new mechanisms that introduce polarization in spectral lines, which turn out to be key for understanding some of the most enigmatic scattering polarization signals of the solar visible spectrum. We also show a radiative transfer prediction on the scattering polarization pattern across the Mg ii h & k lines, whose radiation can only be observed from space
Supriya, H. D.; Smitha, H. N.; Nagendra, K. N.; Stenflo, J. O.; Bianda, M.; Ravindra, B.; Ramelli, R.; Anusha, L. S.
Modeling the center-to-limb variation of the Ca i 4227 Å line using FCHHT models Inproceedings
In: Nagendra, K. N.; Bagnulo, S.; Centeno, R.; Martínez González, M. J. (Ed.): Polarimetry, pp. 381-386, 2015.
@inproceedings{2015IAUS..305..381S,
title = {Modeling the center-to-limb variation of the Ca i 4227 Å line using FCHHT models},
author = {Supriya, H.D. and Smitha, H.N. and Nagendra, K.N. and Stenflo, J.O. and Bianda, M. and Ravindra, B. and Ramelli, R. and Anusha, L.S.},
editor = {Nagendra, K.N. and Bagnulo, S. and Centeno, R. and Martínez González, M.J.},
url = {http://adsabs.harvard.edu/abs/2015IAUS..305..381S},
doi = {10.1017/S1743921315005098},
year = {2015},
date = {2015-01-01},
urldate = {2015-01-01},
booktitle = {Polarimetry},
volume = {305},
pages = {381-386},
series = {IAU Symposium},
abstract = {The Ca i 4227 Å is a chromospheric line exhibiting the largest degree of linear polarization near the limb, in the visible spectrum of the Sun. Modeling the observations of the center-to-limb variations (CLV) of different lines in the Second Solar Spectrum helps to sample the height dependence of the magnetic field, as the observations made at different lines of sight sample different heights in the solar atmosphere. Supriya et al. (2014) attempted to simultaneously model the CLV of the (I, Q/I) spectra of the Ca i 4227 Å line using the standard 1-D FAL model atmospheres. They found that the standard FAL model atmospheres and also any appropriate combination of them, fail to simultaneously fit the observed Stokes (I, Q/I) profiles at all the limb distances (μ) satisfying at the same time all the observational constraints. This failure of 1-D modeling approach can probably be overcome by using multi-dimensional modeling which is computationally expensive. To eliminate an even wider choice of 1-D models, we attempt here to simultaneously model the CLV of the (I, Q/I) spectra using the FCHHT solar model atmospheres which are updated and recent versions of the FAL models. The details of our modeling efforts and the results are presented.},
keywords = {},
pubstate = {published},
tppubtype = {inproceedings}
}
The Ca i 4227 Å is a chromospheric line exhibiting the largest degree of linear polarization near the limb, in the visible spectrum of the Sun. Modeling the observations of the center-to-limb variations (CLV) of different lines in the Second Solar Spectrum helps to sample the height dependence of the magnetic field, as the observations made at different lines of sight sample different heights in the solar atmosphere. Supriya et al. (2014) attempted to simultaneously model the CLV of the (I, Q/I) spectra of the Ca i 4227 Å line using the standard 1-D FAL model atmospheres. They found that the standard FAL model atmospheres and also any appropriate combination of them, fail to simultaneously fit the observed Stokes (I, Q/I) profiles at all the limb distances (μ) satisfying at the same time all the observational constraints. This failure of 1-D modeling approach can probably be overcome by using multi-dimensional modeling which is computationally expensive. To eliminate an even wider choice of 1-D models, we attempt here to simultaneously model the CLV of the (I, Q/I) spectra using the FCHHT solar model atmospheres which are updated and recent versions of the FAL models. The details of our modeling efforts and the results are presented.
2014
Smitha, H. N.; Nagendra, K. N.; Stenflo, J. O.; Sampoorna, M.
The Role of Quantum Interference and Partial Redistribution in the Solar Ba II D2 4554 Å Line Inproceedings
In: Nagendra, K. N.; Stenflo, J. O.; Qu, Q.; Sampoorna, M. (Ed.): Solar Polarization 7, pp. 213, 2014.
@inproceedings{2014ASPC..489..213S,
title = {The Role of Quantum Interference and Partial Redistribution in the Solar Ba II D2 4554 Å Line},
author = {Smitha, H.N. and Nagendra, K.N. and Stenflo, J.O. and Sampoorna, M.},
editor = {Nagendra, K.N. and Stenflo, J.O. and Qu, Q. and Sampoorna, M.},
url = {http://adsabs.harvard.edu/abs/2014ASPC..489..213S},
year = {2014},
date = {2014-10-01},
urldate = {2014-10-01},
booktitle = {Solar Polarization 7},
volume = {489},
pages = {213},
series = {Astronomical Society of the Pacific Conference Series},
abstract = {The Ba II D2 line at 4554 Å is a good example, where the F-state interference effects due to the odd isotopes produce polarization profiles, which are very different from those of the even isotopes that do not exhibit F-state interference. It is therefore necessary to account for the contributions from the different isotopes to understand the observed linear polarization profiles of this line. In this paper we present radiative transfer modeling with partial frequency redistribution, which is shown to be essential to model this line. This is because complete frequency redistribution cannot reproduce the observed wing polarization. We present the observed and computed Q/I profiles at different limb distances. The theoretical profiles strongly depend on limb distance (μ) and the model atmosphere which fits the limb observations fails at other μ positions.},
keywords = {},
pubstate = {published},
tppubtype = {inproceedings}
}
The Ba <font size=2>II D2 line at 4554 Å is a good example, where the F-state interference effects due to the odd isotopes produce polarization profiles, which are very different from those of the even isotopes that do not exhibit F-state interference. It is therefore necessary to account for the contributions from the different isotopes to understand the observed linear polarization profiles of this line. In this paper we present radiative transfer modeling with partial frequency redistribution, which is shown to be essential to model this line. This is because complete frequency redistribution cannot reproduce the observed wing polarization. We present the observed and computed Q/I profiles at different limb distances. The theoretical profiles strongly depend on limb distance (μ) and the model atmosphere which fits the limb observations fails at other μ positions.
Bianda, M.; Ramelli, R.; Gisler, D.; Stenflo, J. O.
Solar Cycle Variations of the Second Solar Spectrum Inproceedings
In: Nagendra, K. N.; Stenflo, J. O.; Qu, Q.; Sampoorna, M. (Ed.): Solar Polarization 7, pp. 167, 2014.
@inproceedings{2014ASPC..489..167B,
title = {Solar Cycle Variations of the Second Solar Spectrum},
author = {Bianda, M. and Ramelli, R. and Gisler, D. and Stenflo, J.O.},
editor = {Nagendra, K.N. and Stenflo, J.O. and Qu, Q. and Sampoorna, M.},
url = {https://www.irsol.usi.ch/data/Papers/SPW7-bianda_4.pdf},
year = {2014},
date = {2014-10-01},
urldate = {2014-10-01},
booktitle = {Solar Polarization 7},
volume = {489},
pages = {167},
series = {Astronomical Society of the Pacific Conference Series},
abstract = {The average strength of the spatially unresolved turbulent magnetic field in the Sun's photosphere can be measured with the Hanle effect. The possible variations of this average value over time scales of a solar cycle is the topic of an ongoing synoptic program at IRSOL that was started in 2008. The scattering polarization of C2 molecular lines around 5140 Å is regularly measured, typically once per month. These lines allow the application of the differential Hanle effect to determine the turbulent field strength. Here we report about the behavior of the determined field strength during the beginning active phase of the solar cycle and about our intention to start a new synoptic program based on the Hanle effect in the Sr I 4607 Å line, with which turbulent field strengths are found that are an order of magnitude larger than those determined with the molecular C2 lines. These synoptic programs allow us to explore the nature of the magnetic fields at the small-scale end of the magnetic scale spectrum and to determine the possible role of a local dynamo for the generation of these fields.},
keywords = {},
pubstate = {published},
tppubtype = {inproceedings}
}
The average strength of the spatially unresolved turbulent magnetic field in the Sun's photosphere can be measured with the Hanle effect. The possible variations of this average value over time scales of a solar cycle is the topic of an ongoing synoptic program at IRSOL that was started in 2008. The scattering polarization of C2 molecular lines around 5140 Å is regularly measured, typically once per month. These lines allow the application of the differential Hanle effect to determine the turbulent field strength. Here we report about the behavior of the determined field strength during the beginning active phase of the solar cycle and about our intention to start a new synoptic program based on the Hanle effect in the Sr I 4607 Å line, with which turbulent field strengths are found that are an order of magnitude larger than those determined with the molecular C2 lines. These synoptic programs allow us to explore the nature of the magnetic fields at the small-scale end of the magnetic scale spectrum and to determine the possible role of a local dynamo for the generation of these fields.
Landi Degl'Innocenti, E.; Belluzzi, L.
Theoretical Schemes for the Interpretation of Solar Polarimetric Observations: An Overview and Some New Ideas Inproceedings
In: Nagendra, K. N.; Stenflo, J. O.; Qu, Q.; Sampoorna, M. (Ed.): Solar Polarization 7, pp. 99, 2014.
@inproceedings{2014ASPC..489...99L,
title = {Theoretical Schemes for the Interpretation of Solar Polarimetric Observations: An Overview and Some New Ideas},
author = {Landi Degl'Innocenti, E. and Belluzzi, L.},
editor = {Nagendra, K.N. and Stenflo, J.O. and Qu, Q. and Sampoorna, M.},
url = {https://www.irsol.usi.ch/data/Papers/landi_belluzzi_spw7.pdf},
year = {2014},
date = {2014-10-01},
urldate = {2014-10-01},
booktitle = {Solar Polarization 7},
volume = {489},
pages = {99},
series = {Astronomical Society of the Pacific Conference Series},
abstract = {The theoretical scheme based on the density matrix formalism, and self-consistently derived from the principles of Quantum Electrodynamics, is presently one of the most solid frameworks for the interpretation of solar polarimetric observations. This scheme has been highly successful, mainly for the interpretation of polarimetric signals that can be described in the so-called limit of complete frequency redistribution (CRD). However, it suffers from the severe limitation that partial frequency redistribution (PRD) effects cannot be accounted for. The metalevel theory can handle PRD effects, but all the attempts for its generalization to account consistently for collisions and lower-level coherences have failed. The redistribution matrix approach is very suitable for taking PRD effects into account. However, it can consistently describe only two-level atoms with unpolarized lower level. New heuristic approaches have been proposed for treating two-term atoms, but they are based on rather crude approximations and their validity and physical consistency are far from being firmly established. Some few reflections that may lead to the establishment of a self-consistent set of equations, fully derived from first principles, are put forward. These reflections are based on the introduction of the Fourier transform of the density matrix.},
keywords = {},
pubstate = {published},
tppubtype = {inproceedings}
}
The theoretical scheme based on the density matrix formalism, and self-consistently derived from the principles of Quantum Electrodynamics, is presently one of the most solid frameworks for the interpretation of solar polarimetric observations. This scheme has been highly successful, mainly for the interpretation of polarimetric signals that can be described in the so-called limit of complete frequency redistribution (CRD). However, it suffers from the severe limitation that partial frequency redistribution (PRD) effects cannot be accounted for. The metalevel theory can handle PRD effects, but all the attempts for its generalization to account consistently for collisions and lower-level coherences have failed. The redistribution matrix approach is very suitable for taking PRD effects into account. However, it can consistently describe only two-level atoms with unpolarized lower level. New heuristic approaches have been proposed for treating two-term atoms, but they are based on rather crude approximations and their validity and physical consistency are far from being firmly established. Some few reflections that may lead to the establishment of a self-consistent set of equations, fully derived from first principles, are put forward. These reflections are based on the introduction of the Fourier transform of the density matrix.
Demidov, M. L.; Stenflo, J. O.; Bianda, M.; Ramelli, R.
Conversion of the 6302 / 6301 Stokes V Line Ratio to the 5250 / 5247 Ratio for the Diagnostics of Quiet-Sun Magnetic Fields Inproceedings
In: Nagendra, K. N.; Stenflo, J. O.; Qu, Q.; Sampoorna, M. (Ed.): Solar Polarization 7, pp. 21, 2014.
@inproceedings{2014ASPC..489...21D,
title = {Conversion of the 6302 / 6301 Stokes V Line Ratio to the 5250 / 5247 Ratio for the Diagnostics of Quiet-Sun Magnetic Fields},
author = {Demidov, M.L. and Stenflo, J.O. and Bianda, M. and Ramelli, R.},
editor = {Nagendra, K.N. and Stenflo, J.O. and Qu, Q. and Sampoorna, M.},
url = {http://adsabs.harvard.edu/abs/2014ASPC..489...21D},
year = {2014},
date = {2014-10-01},
urldate = {2014-10-01},
booktitle = {Solar Polarization 7},
volume = {489},
pages = {21},
series = {Astronomical Society of the Pacific Conference Series},
abstract = {Observations in the "green" spectral lines Fe I 5247.06 and 5250.22 Å and in the "red" lines Fe I 6301.50 and 6302.50 Å are widely used to explore the properties of solar magnetic fields. The green line pair was introduced in 1973 as part of the line-ratio technique, which has been a powerful tool for investigations of intrinsic magnetic field properties at spatially unresolved scales (magnetic flux tubes with kG strengths). The red line pair has recently played a major role for magnetic-field diagnostics due to the large amount of high-quality data provided by the Hinode space observatory. These red lines however differ not only in the values of their Landé factors, but also in their line-formation properties, with the consequence that the magnetic-field information in their line ratio gets tangled up with thermodynamic effects. In contrast, as the green Fe I 5247.06 and 5250.22 Å lines differ only in their Landé factors, the magnetic field effects become cleanly separated from the thermodynamics, which allows the intrinsic magnetic field parameters to be extracted without ambiguties. The red and green line-ratio values are however statistically correlated. By determining the statistical regression function that relates them, it becomes possible to convert the "contaminated" and ambiguous red line ratio into the green line ratio, with which a reliable direct interpretation in terms of intrinsic field strengths is possible. To determine how the two line ratios are related we have made Stokesmeter observations in these four spectral lines with two solar instruments equipped with high-precision spectropolarimeters, ZIMPOL-3 at IRSOL (Locarno, Switzerland), and the STOP telescope at the Sayan Solar Observatory (Irkutsk, Russia). Most of the obtained results are based on IRSOL observations of quiet-sun magnetic fields. In the case of STOP the full-disk magnetograms of large-scale solar magnetic fields are analyzed. A major advantage at IRSOL is the possibility to observe the green and red line pairs simultaneously on the same CCD chip. We have determined how the two line ratios decrease with increasing Stokes V amplitude and increase with increasing distance from disk center. The relation that allows us to convert the observed values for the red line ratio into the corresponding values for the green line ratio has been found and given in analytical form.},
keywords = {},
pubstate = {published},
tppubtype = {inproceedings}
}
Observations in the "green" spectral lines Fe I 5247.06 and 5250.22 Å and in the "red" lines Fe I 6301.50 and 6302.50 Å are widely used to explore the properties of solar magnetic fields. The green line pair was introduced in 1973 as part of the line-ratio technique, which has been a powerful tool for investigations of intrinsic magnetic field properties at spatially unresolved scales (magnetic flux tubes with kG strengths). The red line pair has recently played a major role for magnetic-field diagnostics due to the large amount of high-quality data provided by the Hinode space observatory. These red lines however differ not only in the values of their Landé factors, but also in their line-formation properties, with the consequence that the magnetic-field information in their line ratio gets tangled up with thermodynamic effects. In contrast, as the green Fe I 5247.06 and 5250.22 Å lines differ only in their Landé factors, the magnetic field effects become cleanly separated from the thermodynamics, which allows the intrinsic magnetic field parameters to be extracted without ambiguties. The red and green line-ratio values are however statistically correlated. By determining the statistical regression function that relates them, it becomes possible to convert the "contaminated" and ambiguous red line ratio into the green line ratio, with which a reliable direct interpretation in terms of intrinsic field strengths is possible. To determine how the two line ratios are related we have made Stokesmeter observations in these four spectral lines with two solar instruments equipped with high-precision spectropolarimeters, ZIMPOL-3 at IRSOL (Locarno, Switzerland), and the STOP telescope at the Sayan Solar Observatory (Irkutsk, Russia). Most of the obtained results are based on IRSOL observations of quiet-sun magnetic fields. In the case of STOP the full-disk magnetograms of large-scale solar magnetic fields are analyzed. A major advantage at IRSOL is the possibility to observe the green and red line pairs simultaneously on the same CCD chip. We have determined how the two line ratios decrease with increasing Stokes V amplitude and increase with increasing distance from disk center. The relation that allows us to convert the observed values for the red line ratio into the corresponding values for the green line ratio has been found and given in analytical form.
Stenflo, J. O.
Nature of Quiet-Sun Magnetic Fields Inproceedings
In: Nagendra, K. N.; Stenflo, J. O.; Qu, Q.; Sampoorna, M. (Ed.): Solar Polarization 7, pp. 3, 2014.
@inproceedings{2014ASPC..489....3S,
title = {Nature of Quiet-Sun Magnetic Fields},
author = {Stenflo, J.O.},
editor = {Nagendra, K.N. and Stenflo, J.O. and Qu, Q. and Sampoorna, M.},
url = {http://adsabs.harvard.edu/abs/2014ASPC..489....3S},
year = {2014},
date = {2014-10-01},
urldate = {2014-10-01},
booktitle = {Solar Polarization 7},
volume = {489},
pages = {3},
series = {Astronomical Society of the Pacific Conference Series},
abstract = {Since the magnetic structuring continues to scales of order 10-100 m, far smaller than can possibly be resolved, and since the polarization signals are weak on the quiet Sun, one needs to apply robust diagnostic techniques that do not get biased by measurement noise, are independent of telescope resolution, and have minimal model dependence, in order to reliably determine the intrinsic properties of quiet-sun magnetic fields. Such techniques make use of ensemble averages as the observable signatures of the spatially unresolved domain. Here we show how such concepts are applied to derive the field strengths, sizes, and angular distributions from the observed Hanle depolarization and from the symmetry properties of the transverse Zeeman effect.},
keywords = {},
pubstate = {published},
tppubtype = {inproceedings}
}
Since the magnetic structuring continues to scales of order 10-100 m, far smaller than can possibly be resolved, and since the polarization signals are weak on the quiet Sun, one needs to apply robust diagnostic techniques that do not get biased by measurement noise, are independent of telescope resolution, and have minimal model dependence, in order to reliably determine the intrinsic properties of quiet-sun magnetic fields. Such techniques make use of ensemble averages as the observable signatures of the spatially unresolved domain. Here we show how such concepts are applied to derive the field strengths, sizes, and angular distributions from the observed Hanle depolarization and from the symmetry properties of the transverse Zeeman effect.
Ramelli, R.; Gisler, D.; Bianda, M.; Bello González, N.; Berdyugina, S.; Soltau, D.
First successful deployment of the ZIMPOL-3 system at the GREGOR telescope Inproceedings
In: Ground-based and Airborne Instrumentation for Astronomy V, pp. 91473G, 2014.
@inproceedings{2014SPIE.9147E..3GR,
title = {First successful deployment of the ZIMPOL-3 system at the GREGOR telescope},
author = {Ramelli, R. and Gisler, D. and Bianda, M. and Bello González, N. and Berdyugina, S. and Soltau, D.},
url = {https://www.irsol.usi.ch/data/Papers/ramelli-spie14.pdf},
doi = {10.1117/12.2056934},
year = {2014},
date = {2014-01-01},
urldate = {2014-01-01},
booktitle = {Ground-based and Airborne Instrumentation for Astronomy V},
volume = {9147},
pages = {91473G},
series = {procspie},
abstract = {Since several years the Zurich Imaging polarimeter (ZIMPOL) system is successfully used as a high sensitivity polarimeter. The polarimeter system, which is mainly based on a fast modulator and a special demodulating camera with a masked CCD, has been continuously improved. The third version of the system (ZIMPOL-3) is routinely used at IRSOL, Locarno. The fast modulation allows to "freeze" intensity variations due to seeing, and to achieve a polarimetric sensitivity below 10-5 if the photon statistics is large enough. In October 2013 the ZIMPOL system has been brought and installed for the first time at the GREGOR telescope in Tenerife for a spectropolarimetric observing campaign. There, the system configuration took advantage from the calibration unit installed at the primary focus of the GREGOR telescope, while the analyzer was inserted in the optical path just before the spectrograph slit after several folding mirrors. This setup has been tested successfully by the authors for the first time in this occasion},
keywords = {},
pubstate = {published},
tppubtype = {inproceedings}
}
Since several years the Zurich Imaging polarimeter (ZIMPOL) system is successfully used as a high sensitivity polarimeter. The polarimeter system, which is mainly based on a fast modulator and a special demodulating camera with a masked CCD, has been continuously improved. The third version of the system (ZIMPOL-3) is routinely used at IRSOL, Locarno. The fast modulation allows to "freeze" intensity variations due to seeing, and to achieve a polarimetric sensitivity below 10-5 if the photon statistics is large enough. In October 2013 the ZIMPOL system has been brought and installed for the first time at the GREGOR telescope in Tenerife for a spectropolarimetric observing campaign. There, the system configuration took advantage from the calibration unit installed at the primary focus of the GREGOR telescope, while the analyzer was inserted in the optical path just before the spectrograph slit after several folding mirrors. This setup has been tested successfully by the authors for the first time in this occasion
2013
Stenflo, J. O.
Nature of the solar dynamo at small scales Inproceedings
In: Kosovichev, A. G.; de Gouveia Dal Pino, E.; Yan, Y. (Ed.): Solar and Astrophysical Dynamos and Magnetic Activity, pp. 119-130, 2013.
@inproceedings{2013IAUS..294..119S,
title = {Nature of the solar dynamo at small scales},
author = {Stenflo, J.O.},
editor = {Kosovichev, A.G. and de Gouveia Dal Pino, E. and Yan, Y.},
url = {http://adsabs.harvard.edu/abs/2013IAUS..294..119S},
doi = {10.1017/S1743921313002342},
year = {2013},
date = {2013-07-01},
urldate = {2013-07-01},
booktitle = {Solar and Astrophysical Dynamos and Magnetic Activity},
volume = {294},
pages = {119-130},
series = {IAU Symposium},
abstract = {It is often claimed that there is not only one, but two different types of solar dynamos: the one that is responsible for the appearance of sunspots and the 11-yr cycle, frequently referred to as the ``global dynamo'', and a statistically time-invariant dynamo, generally referred to as the ``local dynamo'', which is supposed to be responsible for the ubiquitous magnetic structuring observed at small scales. Here we examine the relative contributions of these two qualitatively different dynamos to the small-scale magnetic flux, with the following conclusion: The local dynamo does not play a significant role at any of the spatially resolved scales, nearly all the small-scale flux, including the flux revealed by Hinode, is supplied by the global dynamo. This conclusion is reached by careful determination of the Sun's noise-corrected basal magnetic flux density while making use of a flux cancellation function determined from Hinode data. The only allowed range where there may be substantial or even dominating contributions from a local dynamo seems to be the scales below about 10 km, as suggested by observations of the Hanle depolarization effect in atomic spectral lines. To determine the fraction of the Hanle depolarization that may be due to the action of a local dynamo, a synoptic program is being initiated at IRSOL (Istituto Ricerche Solari Locarno).},
keywords = {},
pubstate = {published},
tppubtype = {inproceedings}
}
It is often claimed that there is not only one, but two different types of solar dynamos: the one that is responsible for the appearance of sunspots and the 11-yr cycle, frequently referred to as the ``global dynamo'', and a statistically time-invariant dynamo, generally referred to as the ``local dynamo'', which is supposed to be responsible for the ubiquitous magnetic structuring observed at small scales. Here we examine the relative contributions of these two qualitatively different dynamos to the small-scale magnetic flux, with the following conclusion: The local dynamo does not play a significant role at any of the spatially resolved scales, nearly all the small-scale flux, including the flux revealed by Hinode, is supplied by the global dynamo. This conclusion is reached by careful determination of the Sun's noise-corrected basal magnetic flux density while making use of a flux cancellation function determined from Hinode data. The only allowed range where there may be substantial or even dominating contributions from a local dynamo seems to be the scales below about 10 km, as suggested by observations of the Hanle depolarization effect in atomic spectral lines. To determine the fraction of the Hanle depolarization that may be due to the action of a local dynamo, a synoptic program is being initiated at IRSOL (Istituto Ricerche Solari Locarno).
Bianda, M.; Ramelli, R.; Stenflo, J.; Berdyugina, S.; Gisler, D.; Defilippis, I.; Bello González, N.
The project of installing a ZIMPOL 3 polarimeter at GREGOR in Tenerife Inproceedings
In: pp. 413, 2013.
@inproceedings{2013MmSAI..84..413B,
title = {The project of installing a ZIMPOL 3 polarimeter at GREGOR in Tenerife},
author = {Bianda, M. and Ramelli, R. and Stenflo, J. and Berdyugina, S. and Gisler, D. and Defilippis, I. and Bello González, N.},
year = {2013},
date = {2013-01-01},
urldate = {2013-01-01},
journal = {Mem. Societa Astronomica Italiana},
volume = {84},
pages = {413},
abstract = {A project of collaboration between Kiepenheuer Institut für Sonnenphysik, KIS, and Istituto Ricerche Solari Locarno, IRSOL, includes the installation of a ZIMPOL_3 high resolution polarimeter at the 1.5 meter aperture solar telescope GREGOR in Tenerife. Important scientific topics are expected to be investigated, in particular in the case of events showing faint amplitude polarization signatures like scattering polarization effects, and the Hanle effect. This project has also a technical importance, this combination can be used as test bench for future polarimeters to be installed on the new generation solar telescopes.},
keywords = {},
pubstate = {published},
tppubtype = {inproceedings}
}
A project of collaboration between Kiepenheuer Institut für Sonnenphysik, KIS, and Istituto Ricerche Solari Locarno, IRSOL, includes the installation of a ZIMPOL_3 high resolution polarimeter at the 1.5 meter aperture solar telescope GREGOR in Tenerife. Important scientific topics are expected to be investigated, in particular in the case of events showing faint amplitude polarization signatures like scattering polarization effects, and the Hanle effect. This project has also a technical importance, this combination can be used as test bench for future polarimeters to be installed on the new generation solar telescopes.
Wiehr, E.; Stellmacher, G.; Ramelli, R.; Bianda, M.
The Hot Skin of Prominence Structures Inproceedings
In: pp. 487-494, 2013.
@inproceedings{2013CEAB...37..487W,
title = {The Hot Skin of Prominence Structures},
author = {Wiehr, E. and Stellmacher, G. and Ramelli, R. and Bianda, M.},
url = {https://www.irsol.usi.ch/data/Papers/HvarVortrag12.pdf},
year = {2013},
date = {2013-01-01},
urldate = {2013-01-01},
journal = {Central European Astrophysical Bulletin},
volume = {37},
pages = {487-494},
abstract = {We observe various emission lines in solar prominences and compare the widths of He II 4686 Å, He I 4472 Å (triplet) and He I 5015 Å (singlet) with those of the optically thin Hγ and Mg b_2 lines. The latter two yield a thermal line broadening of 9000
pubstate = {published},
tppubtype = {inproceedings}
}
We observe various emission lines in solar prominences and compare the widths of He II 4686 Å, He I 4472 Å (triplet) and He I 5015 Å (singlet) with those of the optically thin Hγ and Mg b_2 lines. The latter two yield a thermal line broadening of 9000<T_{kin}<11 000 K, which fits the width of He I 5015 Å (singlet). However, He I 4471 Å (triplet) shows an excess of 1.1 indicating an excitation of the triplet in 1.2 times hotter prominence regions. He II 4686 Å is 1.65 times broader and thus emitted in 2.73 times hotter regions of the prominence-corona transition layer, PCTR. The linear radiance relations He tripl/He II=50 and Hγ/He tripl=11.8 suggest a PCTR between each fine-structure thread and the surrounding hot coronal gas.
Setzer, M.; Lübke, S.; Küveler, G.; Zuber, A.; Bianda, M.; Ramelli, R.
Computersteuerung für einen Sonnenspektrografen Inproceedings
In: München DIV Deutscher Industrieverlag 2013, pp. 359, 2013.
@inproceedings{Setzer2013,
title = {Computersteuerung für einen Sonnenspektrografen},
author = {Setzer, M. and Lübke, S. and Küveler, G. and Zuber, A. and Bianda, M. and Ramelli, R.},
year = {2013},
date = {2013-01-01},
booktitle = {München DIV Deutscher Industrieverlag 2013},
pages = {359},
series = {Tagungsband AALE 2013},
keywords = {},
pubstate = {published},
tppubtype = {inproceedings}
}
2012
Frisch, H.; Anusha, L. S.; Bianda, M.; Holzreuter, R.; Nagendra, K. N.; Ramelli, R.; Sampoorna, M.; Smitha, H. N.; Stenflo, J. O.
Forward-scattering Hanle effect in the solar Ca i 4227 Å line Inproceedings
In: Faurobert, M.; Fang, C.; Corbard, T. (Ed.): EAS Publications Series, pp. 59-63, 2012.
@inproceedings{2012EAS....55...59F,
title = {Forward-scattering Hanle effect in the solar Ca i 4227 Å line},
author = {Frisch, H. and Anusha, L.S. and Bianda, M. and Holzreuter, R. and Nagendra, K.N. and Ramelli, R. and Sampoorna, M. and Smitha, H.N. and Stenflo, J.O.},
editor = {Faurobert, M. and Fang, C. and Corbard, T.},
url = {http://www.eas-journal.org/action/displayAbstract?fromPage=online&aid=8626040},
doi = {10.1051/eas/1255007},
year = {2012},
date = {2012-06-01},
urldate = {2012-06-01},
booktitle = {EAS Publications Series},
volume = {55},
pages = {59-63},
series = {EAS Publications Series},
abstract = {High sensitivity spectropolarimetric observations of the four Stokes parameters of the solar Ca I 4227 Å line have been performed in October 2010 at IRSOL with the ZIMPOL polarimeter, near the disk center, outside an active region (Bianda et al. 2011). They were analyzed in Anusha et al. 2011 with a combination of detailed radiative transfer modelling of the Hanle effect for the linear polarization and weak field Zeeman approximation for the circular polarization. This approach made possible a unique determination of the magnetic field vector at various positions along the slit of the spectrograph. A summary of the observations and of their analysis is presented here},
keywords = {},
pubstate = {published},
tppubtype = {inproceedings}
}
High sensitivity spectropolarimetric observations of the four Stokes parameters of the solar Ca I 4227 Å line have been performed in October 2010 at IRSOL with the ZIMPOL polarimeter, near the disk center, outside an active region (Bianda et al. 2011). They were analyzed in Anusha et al. 2011 with a combination of detailed radiative transfer modelling of the Hanle effect for the linear polarization and weak field Zeeman approximation for the circular polarization. This approach made possible a unique determination of the magnetic field vector at various positions along the slit of the spectrograph. A summary of the observations and of their analysis is presented here
Sigismondi, C.; Raponi, A.; De Rosi, G.; Bianda, M.; Ramelli, R.; Caccia, M.; Maspero, M.; Negrini, L.; Wang, X.
Atmospheric fluctuations below 0.1 Hz during drift-scan solar diameter measurements Inproceedings
In: Faurobert, M.; Fang, C.; Corbard, T. (Ed.): EAS Publications Series, pp. 381-383, 2012.
@inproceedings{2012EAS....55..381S,
title = {Atmospheric fluctuations below 0.1 Hz during drift-scan solar diameter measurements},
author = {Sigismondi, C. and Raponi, A. and De Rosi, G. and Bianda, M. and Ramelli, R. and Caccia, M. and Maspero, M. and Negrini, L. and Wang, X.},
editor = {Faurobert, M. and Fang, C. and Corbard, T.},
url = {http://arxiv.org/abs/1112.6187},
doi = {10.1051/eas/1255054},
year = {2012},
date = {2012-01-01},
urldate = {2012-01-01},
booktitle = {EAS Publications Series},
volume = {55},
pages = {381-383},
series = {EAS Publications Series},
abstract = {Measurements of the power spectrum of the seeing in the range 0.001-1 Hz have been performed in order to understand the criticity of the transits method for solar diameter monitoring.},
keywords = {},
pubstate = {published},
tppubtype = {inproceedings}
}
Measurements of the power spectrum of the seeing in the range 0.001-1 Hz have been performed in order to understand the criticity of the transits method for solar diameter monitoring.
Einarsen, L. J.; Rodenhuis, M.; Snik, F.; Keller, C. U.; Stam, D. M.; de Kok, R. J.; Bianda, M.; Ramelli, R.
Multiwavelength imaging polarimetry of Venus at various phase angles Inproceedings
In: Abbasi, A.; Giesen, N. (Ed.): EGU General Assembly Conference Abstracts, pp. 8670, 2012.
@inproceedings{2012EGUGA..14.8670E,
title = {Multiwavelength imaging polarimetry of Venus at various phase angles},
author = {Einarsen, L.J. and Rodenhuis, M. and Snik, F. and Keller, C.U. and Stam, D.M. and de Kok, R.J. and Bianda, M. and Ramelli, R.},
editor = {Abbasi, A. and Giesen, N.},
url = {http://adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2012EGUGA..14.8670E&link_type=ARTICLE&db_key=AST&high=},
year = {2012},
date = {2012-01-01},
urldate = {2012-01-01},
booktitle = {EGU General Assembly Conference Abstracts},
volume = {14},
pages = {8670},
series = {EGU General Assembly Conference Abstracts},
abstract = {Venus is the only planet with an atmosphere that we can observe from the ground at a large range of phase angles. Therefore it constitutes an important benchmark for direct observations of exoplanets, which will soon become available. Moreover, polarimetric observations at various phase angles and wavelengths provide a unique way to characterize any (exo-)planetary atmosphere. For instance, the famous study by Hansen & Hovenier (1974) which combines disk-integrated polarimetric observations and modeling has unambiguously shown that Venus' upper atmosphere consists of sulphuric acid droplets of ~1 um in diameter. We present new spatially resolved observations of Venus using the imaging polarimeters ExPo at the William Herschel Telescope and ZIMPOL at the IRSOL telescope. These observations are taken in narrow-band filters from 364--648 nm, and span phase angles from 10--49 degrees. We find that the degree of polarization varies strongly with wavelength and phase angle, as generally predicted by the model by Hansen & Hovenier. However, the polarization behaviour near the equator differs considerably from that at the poles, hinting at different atmospheric compositions and/or stratifications. In the intensity images we detect a significant shift of the location of maximum intensity with wavelength. These observations allow us to refine the model by Hansen & Hovenier, and we present the preliminary results of our efforts to do so.},
keywords = {},
pubstate = {published},
tppubtype = {inproceedings}
}
Venus is the only planet with an atmosphere that we can observe from the ground at a large range of phase angles. Therefore it constitutes an important benchmark for direct observations of exoplanets, which will soon become available. Moreover, polarimetric observations at various phase angles and wavelengths provide a unique way to characterize any (exo-)planetary atmosphere. For instance, the famous study by Hansen & Hovenier (1974) which combines disk-integrated polarimetric observations and modeling has unambiguously shown that Venus' upper atmosphere consists of sulphuric acid droplets of ~1 um in diameter. We present new spatially resolved observations of Venus using the imaging polarimeters ExPo at the William Herschel Telescope and ZIMPOL at the IRSOL telescope. These observations are taken in narrow-band filters from 364--648 nm, and span phase angles from 10--49 degrees. We find that the degree of polarization varies strongly with wavelength and phase angle, as generally predicted by the model by Hansen & Hovenier. However, the polarization behaviour near the equator differs considerably from that at the poles, hinting at different atmospheric compositions and/or stratifications. In the intensity images we detect a significant shift of the location of maximum intensity with wavelength. These observations allow us to refine the model by Hansen & Hovenier, and we present the preliminary results of our efforts to do so.
Setzer, M.; Küveler, G.; Zuber, A.; Bianda, M.; Ramelli, R.
Automatisierung eines Sonnenspektrografen Inproceedings
In: VIP 2012, 2012.
@inproceedings{Setzer2012,
title = {Automatisierung eines Sonnenspektrografen},
author = {Setzer, M. and Küveler, G. and Zuber, A. and Bianda, M. and Ramelli, R.},
url = {https://www.irsol.usi.ch/data/Papers/setzer2012.pdf},
year = {2012},
date = {2012-01-01},
booktitle = {VIP 2012},
series = {Viruelle Instrumente in der Praxis},
keywords = {},
pubstate = {published},
tppubtype = {inproceedings}
}
2011
Stepan, J.; Trujillo Bueno, J.; Ramelli, R.; Bianda, M.
Scattering polarization and the Hanle effect in Hα as a probe of chromospheric magnetism: Modeling vs. Observations Inproceedings
In: Kuhn, J. R.; Harrington, D. M.; Lin, H.; Berdyugina, S. V.; Trujillo-Bueno, J.; Keil, S. L.; Rimmele, T. (Ed.): Solar Polarization 6, pp. 117, 2011.
@inproceedings{2011ASPC..437..117S,
title = {Scattering polarization and the Hanle effect in Hα as a probe of chromospheric magnetism: Modeling vs. Observations},
author = {Stepan, J. and Trujillo Bueno, J. and Ramelli, R. and Bianda, M.},
editor = {Kuhn, J.R. and Harrington, D.M. and Lin, H. and Berdyugina, S.V. and Trujillo-Bueno, J. and Keil, S.L. and Rimmele, T.},
url = {https://www.irsol.usi.ch/data/Papers/stepan_spw6.pdf},
year = {2011},
date = {2011-04-01},
urldate = {2011-04-01},
booktitle = {Solar Polarization 6},
volume = {437},
pages = {117},
series = {Astronomical Society of the Pacific Conference Series},
abstract = {The Hanle effect in strong spectral lines is the physical mechanism that should be increasingly exploited for quantitative explorations of the magnetism of the quiet solar chromospheric plasma. Here we show, by means of multilevel radiative transfer calculations and new spectropolarimetric observations, that the amplitude and shape of the scattering polarization profiles of the Hα line is very sensitive to the strength and structure of the chromospheric magnetic field. The interpretation of the observations in terms of one-dimensional radiative transfer modeling suggests that there is an abrupt magnetization in the upper chromosphere of the quiet Sun.},
keywords = {},
pubstate = {published},
tppubtype = {inproceedings}
}
The Hanle effect in strong spectral lines is the physical mechanism that should be increasingly exploited for quantitative explorations of the magnetism of the quiet solar chromospheric plasma. Here we show, by means of multilevel radiative transfer calculations and new spectropolarimetric observations, that the amplitude and shape of the scattering polarization profiles of the Hα line is very sensitive to the strength and structure of the chromospheric magnetic field. The interpretation of the observations in terms of one-dimensional radiative transfer modeling suggests that there is an abrupt magnetization in the upper chromosphere of the quiet Sun.
Ramelli, R.; Trujillo Bueno, J.; Bianda, M.; Asensio Ramos, A.
Exploring the Magnetic Fields of Solar Prominences and Spicules via He I D3 spectropolarimetry Inproceedings
In: Kuhn, J. R.; Harrington, D. M.; Lin, H.; Berdyugina, S. V.; Trujillo-Bueno, J.; Keil, S. L.; Rimmele, T. (Ed.): Solar Polarization 6, pp. 109, 2011.
@inproceedings{2011ASPC..437..109R,
title = {Exploring the Magnetic Fields of Solar Prominences and Spicules via He I D3 spectropolarimetry},
author = {Ramelli, R. and Trujillo Bueno, J. and Bianda, M. and Asensio Ramos, A.},
editor = {Kuhn, J.R. and Harrington, D.M. and Lin, H. and Berdyugina, S.V. and Trujillo-Bueno, J. and Keil, S.L. and Rimmele, T.},
url = {https://www.irsol.usi.ch/data/Papers/ramelli_spw6.pdf},
year = {2011},
date = {2011-04-01},
urldate = {2011-04-01},
booktitle = {Solar Polarization 6},
volume = {437},
pages = {109},
series = {Astronomical Society of the Pacific Conference Series},
abstract = {Over the last few years a large set of spectropolarimetric observations of prominences and spicules in the He I D3 multiplet have been collected at the observatory of the
Istituto Ricerche Solari Locarno (IRSOL), using increasingly improved versions of the ZIMPOL polarimeter. The novel HAZEL inversion code of Stokes profiles generated by the joint action of the Hanle and Zeeman effects is being applied to this set of data, in order to infer the strength and geometry of the magnetic field present in these structures. This paper presents a brief overview of the most recent observations and inversions.},
keywords = {},
pubstate = {published},
tppubtype = {inproceedings}
}
Over the last few years a large set of spectropolarimetric observations of prominences and spicules in the He I D3 multiplet have been collected at the observatory of the
Istituto Ricerche Solari Locarno (IRSOL), using increasingly improved versions of the ZIMPOL polarimeter. The novel HAZEL inversion code of Stokes profiles generated by the joint action of the Hanle and Zeeman effects is being applied to this set of data, in order to infer the strength and geometry of the magnetic field present in these structures. This paper presents a brief overview of the most recent observations and inversions.
Istituto Ricerche Solari Locarno (IRSOL), using increasingly improved versions of the ZIMPOL polarimeter. The novel HAZEL inversion code of Stokes profiles generated by the joint action of the Hanle and Zeeman effects is being applied to this set of data, in order to infer the strength and geometry of the magnetic field present in these structures. This paper presents a brief overview of the most recent observations and inversions.
Bianda, M.; Ramelli, R.; Stenflo, J. O.; Anusha, L. S.; Nagendra, K. N.; Sampoorna, M.; Holzreuter, R.; Frisch, H.
Observations of the solar Ca I 4227 Å line Inproceedings
In: Kuhn, J. R.; Harrington, D. M.; Lin, H.; Berdyugina, S. V.; Trujillo-Bueno, J.; Keil, S. L.; Rimmele, T. (Ed.): Solar Polarization 6, pp. 67, 2011.
@inproceedings{2011ASPC..437...67B,
title = {Observations of the solar Ca I 4227 Å line},
author = {Bianda, M. and Ramelli, R. and Stenflo, J.O. and Anusha, L.S. and Nagendra, K.N. and Sampoorna, M. and Holzreuter, R. and Frisch, H.},
editor = {Kuhn, J.R. and Harrington, D.M. and Lin, H. and Berdyugina, S.V. and Trujillo-Bueno, J. and Keil, S.L. and Rimmele, T.},
url = {https://www.irsol.usi.ch/data/Papers/bianda_spw6.pdf},
year = {2011},
date = {2011-04-01},
urldate = {2011-04-01},
booktitle = {Solar Polarization 6},
volume = {437},
pages = {67},
series = {Astronomical Society of the Pacific Conference Series},
abstract = {Our aim is to understand some interesting polarization features observed in the solar Ca I 4277 Å line. Here we only discuss the observational aspects. Observations have also been made in other chromospheric lines within a few hours of those in the Ca I 4227 Å line, in the same region near the north solar limb, to illustrate the potential of simultaneous observations in different lines},
keywords = {},
pubstate = {published},
tppubtype = {inproceedings}
}
Our aim is to understand some interesting polarization features observed in the solar Ca I 4277 Å line. Here we only discuss the observational aspects. Observations have also been made in other chromospheric lines within a few hours of those in the Ca I 4227 Å line, in the same region near the north solar limb, to illustrate the potential of simultaneous observations in different lines
Anusha, L. S.; Stenflo, J. O.; Frisch, H.; Bianda, M.; Holzreuter, R.; Nagendra, K. N.; Sampoorna, M.; Ramelli, R.
Linear Polarization of the Solar Ca I 4227 Å Line: Modeling with Radiative Transfer and Last Scattering Approximation Inproceedings
In: Kuhn, J. R.; Harrington, D. M.; Lin, H.; Berdyugina, S. V.; Trujillo-Bueno, J.; Keil, S. L.; Rimmele, T. (Ed.): Solar Polarization 6, pp. 57, 2011.
@inproceedings{2011ASPC..437...57A,
title = {Linear Polarization of the Solar Ca I 4227 Å Line: Modeling with Radiative Transfer and Last Scattering Approximation},
author = {Anusha, L.S. and Stenflo, J.O. and Frisch, H. and Bianda, M. and Holzreuter, R. and Nagendra, K.N. and Sampoorna, M. and Ramelli, R.},
editor = {Kuhn, J.R. and Harrington, D.M. and Lin, H. and Berdyugina, S.V. and Trujillo-Bueno, J. and Keil, S.L. and Rimmele, T.},
url = {https://www.irsol.usi.ch/data/Papers/anusha_spw6.pdf},
year = {2011},
date = {2011-04-01},
urldate = {2011-04-01},
booktitle = {Solar Polarization 6},
volume = {437},
pages = {57},
series = {Astronomical Society of the Pacific Conference Series},
abstract = {To model the Ca I 4227 Å line polarization, radiative transfer effects with partial frequency redistribution (PRD) must be taken into account. The numerical solution of the relevant polarized radiative transfer (RT) equations is computationally very demanding. The “last scattering approximation” (LSA) is a concept allowing faster methods to be devised. It is based on the remark that a single scattering of the radiation field is sufficient for creating most of the polarization. Its key ingredient is the anisotropy of the radiation field. If the anisotropy is extracted from the observed center to limb variation of the intensity profile, only the wings of the Q/I spectrum can be modeled (Sampoorna et al. 2009). We show here that the core region may be modeled as well if one takes into account the depth variation of the anisotropy which is obtained from an unpolarized multilevel RT (Anusha et al. 2010). After a validation of the LSA approach by comparison with a polarized RT calculation, we apply both approaches to model recent observations of the Ca I 4227 Å line polarization taken on the quiet Sun. Apart from a global scaling factor, both approaches give a very good fit to the Q/I spectrum for all the wavelengths. As the LSA is 8 times faster than the RT approach, we can recommend it as an efficient method to analyze other strong resonance lines in the second solar spectrum},
keywords = {},
pubstate = {published},
tppubtype = {inproceedings}
}
To model the Ca I 4227 Å line polarization, radiative transfer effects with partial frequency redistribution (PRD) must be taken into account. The numerical solution of the relevant polarized radiative transfer (RT) equations is computationally very demanding. The “last scattering approximation” (LSA) is a concept allowing faster methods to be devised. It is based on the remark that a single scattering of the radiation field is sufficient for creating most of the polarization. Its key ingredient is the anisotropy of the radiation field. If the anisotropy is extracted from the observed center to limb variation of the intensity profile, only the wings of the Q/I spectrum can be modeled (Sampoorna et al. 2009). We show here that the core region may be modeled as well if one takes into account the depth variation of the anisotropy which is obtained from an unpolarized multilevel RT (Anusha et al. 2010). After a validation of the LSA approach by comparison with a polarized RT calculation, we apply both approaches to model recent observations of the Ca I 4227 Å line polarization taken on the quiet Sun. Apart from a global scaling factor, both approaches give a very good fit to the Q/I spectrum for all the wavelengths. As the LSA is 8 times faster than the RT approach, we can recommend it as an efficient method to analyze other strong resonance lines in the second solar spectrum
Sigismondi, C.; Raponi, A.; Wang, X.; De Rosi, G.; Bianda, M.; Ramelli, R.
The power spectrum of the seeing during solar observations Inproceedings
In: 2011.
@inproceedings{2011arXiv1112.0401S,
title = {The power spectrum of the seeing during solar observations},
author = {Sigismondi, C. and Raponi, A. and Wang, X. and De Rosi, G. and Bianda, M. and Ramelli, R.},
url = {http://arxiv.org/abs/1112.0401},
year = {2011},
date = {2011-01-01},
urldate = {2011-01-01},
journal = {ArXiv e-prints},
abstract = {Measurements of the power spectrum of the atmospheric seeing in the line of sight of the Sun, in the range 0.001-1 Hz, have been performed in Santa Maria degli Angeli Lucernaria Dome, at IRSOL and in Huairou Station. This study is aimed to understand the criticity of the meridian transits method for solar diameter monitoring},
keywords = {},
pubstate = {published},
tppubtype = {inproceedings}
}
Measurements of the power spectrum of the atmospheric seeing in the line of sight of the Sun, in the range 0.001-1 Hz, have been performed in Santa Maria degli Angeli Lucernaria Dome, at IRSOL and in Huairou Station. This study is aimed to understand the criticity of the meridian transits method for solar diameter monitoring
2010
Ramelli, R.; Bucher, R.; Rossini, L.; Bianda, M.; Balemi, S.
Adaptive optics system for the IRSOL solar observatory Inproceedings
In: Adaptive Optics Systems II, pp. 77363K, 2010.
@inproceedings{2010SPIE.7736E..3KR,
title = {Adaptive optics system for the IRSOL solar observatory},
author = {Ramelli, R. and Bucher, R. and Rossini, L. and Bianda, M. and Balemi, S.},
url = {https://www.irsol.usi.ch/data/Papers/ao_spie10.pdf},
doi = {10.1117/12.857160},
year = {2010},
date = {2010-07-01},
urldate = {2010-07-01},
booktitle = {Adaptive Optics Systems II},
volume = {7736},
pages = {77363K},
series = {procspie},
abstract = {We present a low cost adaptive optics system developed for the solar observatory at Istituto Ricerche Solari Locarno (IRSOL), Switzerland. The Shack-Hartmann Wavefront Sensor is based on a Dalsa CCD camera with 256 pixels × 256 pixels working at 1kHz. The wavefront compensation is obtained by a deformable mirror with 37 actuators and a Tip-Tilt mirror. A real time control software has been developed on a RTAI-Linux PC. Scicos/Scilab based software has been realized for an online analysis of the system behavior. The software is completely open source.},
keywords = {},
pubstate = {published},
tppubtype = {inproceedings}
}
We present a low cost adaptive optics system developed for the solar observatory at Istituto Ricerche Solari Locarno (IRSOL), Switzerland. The Shack-Hartmann Wavefront Sensor is based on a Dalsa CCD camera with 256 pixels × 256 pixels working at 1kHz. The wavefront compensation is obtained by a deformable mirror with 37 actuators and a Tip-Tilt mirror. A real time control software has been developed on a RTAI-Linux PC. Scicos/Scilab based software has been realized for an online analysis of the system behavior. The software is completely open source.
Ramelli, R.; Balemi, S.; Bianda, M.; Defilippis, I.; Gamma, L.; Hagenbuch, S.; Rogantini, M.; Steiner, P.; Stenflo, J. O.
ZIMPOL-3: a powerful solar polarimeter Inproceedings
In: Ground-based and Airborne Instrumentation for Astronomy III, pp. 77351Y, 2010.
@inproceedings{2010SPIE.7735E..1YR,
title = {ZIMPOL-3: a powerful solar polarimeter},
author = {Ramelli, R. and Balemi, S. and Bianda, M. and Defilippis, I. and Gamma, L. and Hagenbuch, S. and Rogantini, M. and Steiner, P. and Stenflo, J.O.},
url = {https://www.irsol.usi.ch/data/Papers/zimpol_spie10.pdf},
doi = {10.1117/12.857120},
year = {2010},
date = {2010-07-01},
urldate = {2010-07-01},
booktitle = {Ground-based and Airborne Instrumentation for Astronomy III},
volume = {7735},
pages = {77351Y},
series = {procspie},
abstract = {The area of high precision solar spectropolarimetry has made great advances in recent years and the Zurich IMaging POLarimeter (ZIMPOL) systems have played a major role in that. ZIMPOL reaches a polarimetric accuracy of 10-5 by using fast (kHz) polarization modulation/demodulation of the light beam in combination with large-area array detectors. A new generation of improved cameras (ZIMPOL-3) are being implemented for the scientific observations at the solar observatory at Istituto Ricerche Solari Locarno. The new system is based on a flexible and compact modular design, which easily adapts to new applications. A faster electronics and new sensors with higher quantum efficency compared to the previous ZIMPOL versions, allow to achieve a better overall efficency. Future plans include observing campaigns at foremost large telescopes and the exploration of new technologies (e.g. CMOS).},
keywords = {},
pubstate = {published},
tppubtype = {inproceedings}
}
The area of high precision solar spectropolarimetry has made great advances in recent years and the Zurich IMaging POLarimeter (ZIMPOL) systems have played a major role in that. ZIMPOL reaches a polarimetric accuracy of 10-5 by using fast (kHz) polarization modulation/demodulation of the light beam in combination with large-area array detectors. A new generation of improved cameras (ZIMPOL-3) are being implemented for the scientific observations at the solar observatory at Istituto Ricerche Solari Locarno. The new system is based on a flexible and compact modular design, which easily adapts to new applications. A faster electronics and new sensors with higher quantum efficency compared to the previous ZIMPOL versions, allow to achieve a better overall efficency. Future plans include observing campaigns at foremost large telescopes and the exploration of new technologies (e.g. CMOS).