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Issue A&A
Volume 419, Number 2, May IV 2004
Page(s) 549 - 561
Section Interstellar and circumstellar matter
DOI http://dx.doi.org/10.1051/0004-6361:20035797



A&A 419, 549-561 (2004)
DOI: 10.1051/0004-6361:20035797

The circumstellar environments of EP Aqr and Y CVn probed by the H I emission at 21 cm

T. Le Bertre1 and E. Gérard2

1  LERMA, UMR 8112, Observatoire de Paris, 61 av. de l'Observatoire, 75014 Paris, France
2  GEPI, UMR 8111, Observatoire de Paris, 5 place J. Janssen, 92195 Meudon Cedex, France

(Received 3 December 2003 / Accepted 3 February 2004 )

Abstract
The H I line at 21 cm has been detected in the circumstellar shells of the two semi-regular variables, EP Aqr and Y CVn, with the Nançay Radio-Telescope (NRT). In both cases the line shape is composite and the emission is spatially extended compared to the NRT beam size (4´). The total H I masses of the two envelopes are respectively ~0.047  $M_{\odot}$  and 0.044  $M_{\odot}$. For EP Aqr, we find three components: a narrow one centered on the star and spatially unresolved, and two broad, Gaussian components, offset w.r.t. the star and spatially extended. The narrow component traces the present wind from EP Aqr whereas the two others seem to trace one or several mass-loss episodes of long duration. For Y CVn, we find two components: a narrow, spatially very extended, feature, and a broad one, less extended. We argue that the second component traces the outflow and the first one, its interaction with the ISM. These observations show that the H I emission can be used not only to probe the mass loss history of long-period variables, but also to investigate the interaction between stellar outflows and the surrounding ISM.


Key words: stars: circumstellar matter -- stars: mass-loss -- stars: individual: EP Aqr -- stars: individual: Y CVn -- stars: AGB and post-AGB

Offprint request: T. Le Bertre, Thibaut.LeBertre@obspm.fr

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© ESO 2004


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