Download First image of the visible photosphere of a star other than the Sun

First image of the visible photosphere of a star other than the Sun
Extrait du Observatoire de Paris centre de recherche et enseignement en astronomie et
astrophysique relevant du Ministère de l'Enseignement supérieur et de la Recherche.
https://www.obspm.fr/first-image-of-the-visible.html
First image of the visible
photosphere of a star other
than the Sun
Date de mise en ligne : mardi 24 novembre 2015
Observatoire de Paris centre de recherche et enseignement en astronomie et
astrophysique relevant du Ministère de l'Enseignement supérieur et de la
Recherche.
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First image of the visible photosphere of a star other than the Sun
Using the new extreme adaptive optics system SPHERE of ESO's Very Large Telescope, an
international team led by a Paris Observatory astronomer has obtained the first image of the
visible surface of a star other than the Sun, the red supergiant Betelgeuse.
Image composite couleur de Bételgeuse : première image couleur de la photosphère d'une étoile autre que
le Soleil, issue des observations SPHERE/ZIMPOL. La résolution du télescope est représentée par l'ellipse
blanche dans le coin inférieur gauche de l'image.
Betelgeuse is one of the largest stars known, with a radius of 700 times the Sun's.
Thanks to its proximity ( 640 light-years), its apparent diameter (45 milliarcseconds) is among the largest of all stars.
It is equivalent to the apparent size of a 1Euros coin observed at a distance of 100 kilometers.
The vivid orange color of the supergiant star (± Orionis) is one of the most remarkable sights of the winter sky. This
hue is caused by its particularly low surface temperature of approximately 4000°C (compared to 6000°C for the Sun).
As it is a massive star, Betelgeuse has a very short lifetime of about ten million years, and it will likely end in a
powerful supernova explosion within the next million year.
Betelgeuse : a prime target
Betelgeuse is currently loosing mass at a rate of several Earth masses per year, enriching the interstellar medium
with chemical elements produced by the nuclear reactions (oxygen, carbon, silicium,...). They expand from the star's
surface, forming molecules and dust as they cool down. Evolved stars as Betelgeuse thus play a central role in the
chemical evolution of the Universe.
How the material is expelled from the surface of the star is still largely mysterious, and Betelgeuse is a prime target to
study this phenomenon.
This is the reason why Betelgeuse was observed in March 2015 by an international team led by Pierre Kervella
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First image of the visible photosphere of a star other than the Sun
(CNRS UMI FCA & LESIA, Paris Observatory) using the new SPHERE/ZIMPOL instrument of the European
Southern Observatory's Very Large Telescope (Cerro Paranal, Chile).
SPHERE is a new generation extreme adaptive optics system that corrects very efficiently the perturbations of the
atmosphere. This resulting images are diffraction-limited, achieving the theoretical resolution limit of the telescope
down to visible wavelengths.
Precious hints on the mass-loss mechanism
The SPHERE color image of Betelgeuse as it would appear to the human eye is presented in Fig. 1. This is the first
image of the visible surface (the photosphere) of a star other than the Sun. The white ellipse shows the resolution
element of the telescope. The photosphere of Betelgeuse appears irregular and surrounded by gaseous plumes.
These asymmetries strengthen previous indications that the mass loss of Betelgeuse is likely tied to the vigorous
convective motions in its atmosphere.
The ZIMPOL camera also measures the polarization of the light, that is caused by the scattering of the stellar light by
the dust surrounding the star.
Carte du taux de polarisation linéaire autour de Bételgeuse. La taille moyenne de la photosphère est
représentée par un cercle en pointillés rouges, et le cercle jaune marque 3 fois le rayon de l'étoile.
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First image of the visible photosphere of a star other than the Sun
The polarization map (Fig. 2) indicates that dust is present in an asymmetric and incomplete dust shell at an altitude
of approximately 3 times the star's radius.
The presence of dust grains so close to the star indicates that they likely play an important role in the mass-loss
mechanism.
These observations bring precious hints on the way through which massive stars loose their matter and enrich the
interstellar medium.
Référence
« The close circumstellar environment of Betelgeuse. III. SPHERE/ZIMPOL imaging polarimetry in the visible »,
Astronomy and Astrophysics, Novembre 2015.
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http://dx.doi.org/10.1051/0004-6361...
http://arxiv.org/abs/1511.04451
Science team
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P. Kervella (Laboratoire Franco-Chilien d'Astronomie, CNRS UMI 3386 & LESIA/ Observatoire de Paris),
E. Lagadec (Observatoire de la Côte d'Azur),
M. Montargès (IRAM),
S. T. Ridgway (NOAO, USA),
A. Chiavassa (Observatoire de la Côte d'Azur),
X. Haubois (ESO Chili), H.-M. Schmid (ETH Zürich, Suisse),
M. Langlois (CRAL/Observatoire de Lyon),
A. Gallenne (Université de Concepcion, Chili & ESO Chili)
G. Perrin (LESIA/Observatoire de Paris)
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