Discovery of a complex linearly polarized spectrum of Betelgeuse dominated by depolarization of the continuum
Betelgeuse is an M supergiant that harbors spots and giant granules at its surface and presents linear polarization of its continuum. We have previously discovered linear polarization signatures associated with individual lines in the spectra of cool and evolved stars. Here, we investigate whether a...
Published in: | Astronomy & Astrophysics |
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Main Authors: | , , , , , , , , , , , , , , , , , |
Format: | Article in Journal/Newspaper |
Language: | English |
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Online Access: | https://doi.org/10.1051/0004-6361/201628077 |
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ftoskarbordeaux:oai:oskar-bordeaux.fr:20.500.12278/95832 2024-05-19T07:50:08+00:00 Discovery of a complex linearly polarized spectrum of Betelgeuse dominated by depolarization of the continuum AURIÈRE, M., LÓPEZ ARISTE, A., MATHIAS, P., LÈBRE, Agnès JOSSELIN, E., MONTARGÈS, M., PETIT, P., CHIAVASSA, A., PALETOU, F., FABAS, N., KONSTANTINOVA-ANTOVA, R., DONATI, J.-F., GRUNHUT, J. H., WADE, G. A., HERPIN, Fabrice KERVELLA, P., PERRIN, G., TESSORE, B. 2016-05 https://doi.org/10.1051/0004-6361/201628077 en eng EDP Sciences 0004-6361 doi:10.1051/0004-6361/201628077 1605.04702 Astrophysics - Solar and Stellar Astrophysics Planète et Univers [physics]/Astrophysique [astro-ph]/Astrophysique galactique [astro-ph.GA] Article de revue 2016 ftoskarbordeaux https://doi.org/10.1051/0004-6361/201628077 2024-04-22T01:37:18Z Betelgeuse is an M supergiant that harbors spots and giant granules at its surface and presents linear polarization of its continuum. We have previously discovered linear polarization signatures associated with individual lines in the spectra of cool and evolved stars. Here, we investigate whether a similar linearly polarized spectrum exists for Betelgeuse. We used the spectropolarimeter Narval, combining multiple polarimetric sequences to obtain high signal-to-noise ratio spectra of individual lines, as well as the least-squares deconvolution (LSD) approach. We have discovered the existence of a linearly polarized spectrum for Betelgeuse, detecting a rather strong signal (at a few times 10$^{-4}$ of the continuum intensity level), both in individual lines and in the LSD profiles. Studying its properties and the signal observed for the resonant \ion{Na}{i}\,D lines, we conclude that we are mainly observing depolarization of the continuum by the absorption lines. The linear polarization of the Betelgeuse continuum is due to the anisotropy of the radiation field induced by brightness spots at the surface and Rayleigh scattering in the atmosphere. We have developed a geometrical model to interpret the observed polarization, from which we infer the presence of two brightness spots and their positions on the surface of Betelgeuse. We show that applying the model to each velocity bin along the Stokes Q and U profiles allows the derivation of a map of the bright spots. We use the Narval linear polarization observations of Betelgeuse obtained over a period of 1.4 years to study the evolution of the spots. Our study of the linearly polarized spectrum of Betelgeuse provides a novel method for studying the evolution of brightness spots at its surface and complements quasi-simultaneous observations obtained with PIONIER at the VLTI. Article in Journal/Newspaper narval narval OSKAR Bordeaux (Open Science Knowledge ARchive) Astronomy & Astrophysics 591 A119 |
institution |
Open Polar |
collection |
OSKAR Bordeaux (Open Science Knowledge ARchive) |
op_collection_id |
ftoskarbordeaux |
language |
English |
topic |
Astrophysics - Solar and Stellar Astrophysics Planète et Univers [physics]/Astrophysique [astro-ph]/Astrophysique galactique [astro-ph.GA] |
spellingShingle |
Astrophysics - Solar and Stellar Astrophysics Planète et Univers [physics]/Astrophysique [astro-ph]/Astrophysique galactique [astro-ph.GA] AURIÈRE, M., LÓPEZ ARISTE, A., MATHIAS, P., LÈBRE, Agnès JOSSELIN, E., MONTARGÈS, M., PETIT, P., CHIAVASSA, A., PALETOU, F., FABAS, N., KONSTANTINOVA-ANTOVA, R., DONATI, J.-F., GRUNHUT, J. H., WADE, G. A., HERPIN, Fabrice KERVELLA, P., PERRIN, G., TESSORE, B. Discovery of a complex linearly polarized spectrum of Betelgeuse dominated by depolarization of the continuum |
topic_facet |
Astrophysics - Solar and Stellar Astrophysics Planète et Univers [physics]/Astrophysique [astro-ph]/Astrophysique galactique [astro-ph.GA] |
description |
Betelgeuse is an M supergiant that harbors spots and giant granules at its surface and presents linear polarization of its continuum. We have previously discovered linear polarization signatures associated with individual lines in the spectra of cool and evolved stars. Here, we investigate whether a similar linearly polarized spectrum exists for Betelgeuse. We used the spectropolarimeter Narval, combining multiple polarimetric sequences to obtain high signal-to-noise ratio spectra of individual lines, as well as the least-squares deconvolution (LSD) approach. We have discovered the existence of a linearly polarized spectrum for Betelgeuse, detecting a rather strong signal (at a few times 10$^{-4}$ of the continuum intensity level), both in individual lines and in the LSD profiles. Studying its properties and the signal observed for the resonant \ion{Na}{i}\,D lines, we conclude that we are mainly observing depolarization of the continuum by the absorption lines. The linear polarization of the Betelgeuse continuum is due to the anisotropy of the radiation field induced by brightness spots at the surface and Rayleigh scattering in the atmosphere. We have developed a geometrical model to interpret the observed polarization, from which we infer the presence of two brightness spots and their positions on the surface of Betelgeuse. We show that applying the model to each velocity bin along the Stokes Q and U profiles allows the derivation of a map of the bright spots. We use the Narval linear polarization observations of Betelgeuse obtained over a period of 1.4 years to study the evolution of the spots. Our study of the linearly polarized spectrum of Betelgeuse provides a novel method for studying the evolution of brightness spots at its surface and complements quasi-simultaneous observations obtained with PIONIER at the VLTI. |
format |
Article in Journal/Newspaper |
author |
AURIÈRE, M., LÓPEZ ARISTE, A., MATHIAS, P., LÈBRE, Agnès JOSSELIN, E., MONTARGÈS, M., PETIT, P., CHIAVASSA, A., PALETOU, F., FABAS, N., KONSTANTINOVA-ANTOVA, R., DONATI, J.-F., GRUNHUT, J. H., WADE, G. A., HERPIN, Fabrice KERVELLA, P., PERRIN, G., TESSORE, B. |
author_facet |
AURIÈRE, M., LÓPEZ ARISTE, A., MATHIAS, P., LÈBRE, Agnès JOSSELIN, E., MONTARGÈS, M., PETIT, P., CHIAVASSA, A., PALETOU, F., FABAS, N., KONSTANTINOVA-ANTOVA, R., DONATI, J.-F., GRUNHUT, J. H., WADE, G. A., HERPIN, Fabrice KERVELLA, P., PERRIN, G., TESSORE, B. |
author_sort |
AURIÈRE, M., |
title |
Discovery of a complex linearly polarized spectrum of Betelgeuse dominated by depolarization of the continuum |
title_short |
Discovery of a complex linearly polarized spectrum of Betelgeuse dominated by depolarization of the continuum |
title_full |
Discovery of a complex linearly polarized spectrum of Betelgeuse dominated by depolarization of the continuum |
title_fullStr |
Discovery of a complex linearly polarized spectrum of Betelgeuse dominated by depolarization of the continuum |
title_full_unstemmed |
Discovery of a complex linearly polarized spectrum of Betelgeuse dominated by depolarization of the continuum |
title_sort |
discovery of a complex linearly polarized spectrum of betelgeuse dominated by depolarization of the continuum |
publisher |
EDP Sciences |
publishDate |
2016 |
url |
https://doi.org/10.1051/0004-6361/201628077 |
genre |
narval narval |
genre_facet |
narval narval |
op_relation |
0004-6361 doi:10.1051/0004-6361/201628077 1605.04702 |
op_doi |
https://doi.org/10.1051/0004-6361/201628077 |
container_title |
Astronomy & Astrophysics |
container_volume |
591 |
container_start_page |
A119 |
_version_ |
1799468722930319360 |