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

V Hya, an evolved carbon star with a complex circumstellar envelope, has two variability periods. 530^d and 6000^d ( 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 530^d period and its 1.5^m-2^m 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 si/e 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.

Duke Scholars

Author Ken H Young Pathology