Hipparcos Observations of Hydrogen-deficient Carbon Stars

P. L. Cottrell
W. A. Lawson

Mount John University Observatory, Department of Physics and Astronomy,
University of Canterbury, Christchurch, New Zealand
p.cottrell@phys.canterbury.ac.nz
School of Physics, University College UNSW, Australian Defence Force Academy,
Canberra ACT 2600, Australia
w-lawson@adfa.oz.au

Abstract:

Parallax measurements for 21 hydrogen-deficient carbon stars have been made by the Hipparcos satellite. These stars include most of the brighter R Coronae Borealis (RCB) variables, other cool hydrogen-deficient carbon (HdC) stars, and several higher- extreme helium (eHe) stars. Most of these stars have either negative or statistically insignificant parallaxes, indicating that they lie beyond the detection capability of Hipparcos. Although the distances to the galactic hydrogen-deficient carbon stars remain unknown, at least the Hipparcos observations do confirm that these objects must have high luminosity like the LMC RCB stars, for which = -4 to -5. Based upon Hipparcos proper motions, we derive UVW velocities for the RCB and HdC stars, assuming = -3 and -5. The UW-velocity dispersion of the RCB/HdC stars is similar to that already reported for the eHe stars, further supporting that these groups of stars have predominantly bulge distributions. However, UW Cen may be a second example of a halo RCB star currently seen transitting the galactic plane.

Keywords: stars: AGB and post-AGB - stars: carbon - stars: distances
stars: fundamental parameters - stars: kinematics

© Copyright Astronomical Society of Australia 1997