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Astron. Astrophys. 351, 97-102 (1999)

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The light curve and evolutionary status of the carbon star V Hya

G.R. Knapp 1, S.I. Dobrovolsky 1, Z. Ivezi 1, K. Young 2, M. Crosas 2, J.A. Mattei 3 and M.P. Rupen 4

1 Department of Astrophysical Sciences, Princeton University, Princeton, NJ 08544, USA (gk, sid, ivezic@astro.princeton.edu)
2 Harvard-Smithsonian Center for Astrophysics, 60 Garden St., Cambridge, MA 02138, USA (rtm, mcrosas@dolson.harvard.edu)
3 American Association of Variable Star Observers, 25 Birch St., Cambridge, MA 02128-1205, USA (jmattei@aavso.org)
4 National Radio Astronomy Observatory, P.O. Box 0, 1003 Lopezville Rd., Socorro, NM 87801, USA (mrupen@nrao.edu)

Received 15 December 1998 / Accepted 1 July 1999

Abstract

V Hya, an evolved carbon star with a complex circumstellar envelope, has two variability periods, [FORMULA] and [FORMULA] (17 years). We analyze recent light curve data and show that both variations have been present for at least 100 years and have been regular over this time. The [FORMULA] period and its [FORMULA]-[FORMULA] amplitude show that V Hya is a Mira variable. We suggest that the star is in a binary system (as also suspected from the structure of the circumstellar envelope) and that the 17-year variation is due to extinction by circumstellar dust orbiting with the companion. The properties of the envelope found from molecular line observations: the fast molecular wind, the relatively small size of the dense circumstellar envelope, and the high mass loss rate, all suggest that V Hya has entered its `superwind' phase. However, its spectral type, period, colors, and lack of ionizing radiation show that the star is still on the AGB. These properties add to the evidence that the complex structures of many planetary nebulae, including fast stellar winds, originate during the final phases of mass loss on the AGB.

Key words: stars: mass-loss – stars: AGB and post-AGB – radio lines: stars

Send offprint requests to: G.R. Knapp

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© European Southern Observatory (ESO) 1999

Online publication: November 2, 1999
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