Winds in R Coronae Borealis Stars

We present new spectroscopic observations of the He I λ10830 line in R Coronae Borealis (RCB) stars which provide the first strong evidence that most, if not all, RCB stars have winds. It has long been suggested that when dust forms around an RCB star, radiation pressure accelerates the dust away from the star, dragging the gas along with it. The new spectra show that nine of the ten stars observed have P-Cygni or asymmetric blue-shifted profiles in the He I λ10830 line. In all cases, the He I line indicates a mass outflow with a range of intensity and velocity. Around the RCB stars, it is likely that this state is populated by collisional excitation rather than photoionization/recombination. The line profiles have been modeled with an SEI code to derive the optical depth and the velocity field of the helium gas. The results show that the typical RCB wind has a steep acceleration with a terminal velocity of V∞ = 200-350 km s −1 and a column density of N ∼10 cm in the He I λ10830 line. There is a possible relationship between the lightcurve of an RCB star and its He I λ10830 profile. Stars which have gone hundreds of days with no dust-formation episodes tend to have weaker He I features. The unusual RCB star, V854 Cen, does not follow this trend, showing little or no He I absorption despite high mass-loss activity. The He I λ10830 line in R CrB itself, which has been observed at four epochs between 1978 and 2001, seems to show a P-Cygni or asymmetric blue-shifted profile at all times whether it is in decline or at maximum light. Subject headings: Variable stars, R Coronae Borealis stars, P-Cygni Department of Physics & Astronomy, Louisiana State University Baton Rouge, LA 70803 email: [email protected] Gemini Observatory, 670 N. A’ohoku Place, Hilo, HI 96720 email: [email protected] Center for Astrophysical Sciences, The Johns Hopkins University, Department of Physics and Astronomy, 239 Bloomberg Center for Physics and Astronomy, 3400 North Charles Street, Baltimore, MD 21218 email: [email protected]