Journal Article

Discovery of a detached H <span class="smallCaps">i</span> gas shell surrounding α Orionis

T. Le Bertre, L. D. Matthews, E. Gérard and Y. Libert

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 422, issue 4, pages 3433-3443
Published in print June 2012 | ISSN: 0035-8711
Published online May 2012 | e-ISSN: 1365-2966 | DOI:
Discovery of a detached H i gas shell surrounding α Orionis

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We report the detection of the H i line at 21 cm in the direction of α Orionis (α Ori) with the Nançay Radiotelescope and with the Very Large Array.

The observations confirm the previous detection of H i emission centred on α Ori, but additionally reveal for the first time a quasi-stationary detached shell of neutral atomic hydrogen ∼4 arcmin in diameter (0.24 pc at a distance of 200 pc). The detached shell appears elongated in a direction opposite to the star’s space motion.

A simple model shows that this detached atomic gas shell can result from the collision of the stellar wind from α Ori with the local interstellar medium (ISM). It implies that α Ori has been losing matter at a rate of ∼1.2 × 10−6 M yr−1 for the past 8 × 104 yr.

In addition, we report the detection of atomic hydrogen associated with the far-infrared arc located 6 arcmin north-east of α Ori, which has been suggested to trace the bow shock resulting from the motion of the star through the ISM. We also report the detection by the Galaxy Evolution Explorer of a far-ultraviolet counterpart to this arc.

Keywords: circumstellar matter; stars: individual: α Ori; stars: mass-loss; supergiants; radio lines: stars

Journal Article.  8420 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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