Winds in R Coronae Borealis Stars

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Abstract
We present new spectroscopic observations of the He I λ10830 line in R Coronae Borealis (RCB) stars that 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 10 stars observed have P Cygni or asymmetric blueshifted 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 ~ 1012 cm-2 in the He I λ10830 line. There is a possible relationship between the light curve of an RCB star and its He I λ10830 profile. Stars that 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 1972 and 2001, seems to show a P Cygni or asymmetric blueshifted profile at all times, whether it is in decline or at maximum light.
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