EVIDENCE FOR RAPID ROTATION OF THE CARBON STAR V-HYDRAE

The carbon star V Hya is known to have a bipolar circumstellar outflow and an unusual photospheric spectrum. After measuring the changes in the photospheric velocity and carrying out a spectral broadening analy sis over 10 photometric phases, we conclude that rotation due to spin- up by a companion in a common envelope configuration is the most compe lling explanation for all the data taken together. After considering t he spectral and velocity behavior of 74 other carbon stars, we find th at V Hya is alone in our sample in having such obvious phase-dependent broadening. In this paper we detail the broadening results and explor e other possible causes of spectral broadening in late-type stars. In particular, we find that: (1) the spectral broadening in V Hya varies about a mean value of 13.5 km s(-1) (with total variation of 9 km s(-1 )) in concert with the photometric phase and with a phase relationship consistent with that expected for a rapidly rotating star that conser ves angular momentum as it pulsates, (2) V Hya's unusual, very long se condary period of 6500 days might be attributed to a coupling of radia l pulsation (529 day period) with rotation, (3) the upper limit on the ultraviolet continuum flux favors a common envelope versus detached b inary system, (4) the variability type, Mira versus semiregular variab le, is uncertain since V Hya demonstrates spectral characteristics of both, and (5) the evolutionary placement on the asymptotic giant branc h is in question since V Hya appears to lack Tc-99, a signature elemen t of third dredge-up whose absence suggests that a mass transfer event in the past might be responsible for V Hya's carbon and s-process ele ment enhancement.