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Hipparcos Observations of Hydrogen-deficient Carbon Stars*

Published online by Cambridge University Press:  05 March 2013

P. L. Cottrell  and
W. A. Lawson
P. L. Cottrell
Affiliation:
Mount John University Observatory, Department of Physics and Astronomy, University of Canterbury, Christchurch, New Zealand; p.cottrell@phys.canterbury.ac.nz
W. A. Lawson
Affiliation:
School of Physics, University College, UNSW, Australian Defence Force Academy, Canberra, ACT 2600, Australia; w-lawson@adfa.oz.au
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Abstract

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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-Teff 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 Mbol = −4 to −5. Based upon Hipparcos proper motions, we derive UVW velocities for the RCB and HdC stars, assuming Mbol = −3 and −5. The UW -velocity dispersion of the RCB/HdC stars is similar to that already reported for the eHe stars, further supporting the idea 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-AGBstars: carbonstars: distancesstars: fundamental parametersstars: kinematics
Type
Research Article
Information
Publications of the Astronomical Society of Australia , Volume 15 , Issue 2 , 1998 , pp. 179 - 182
Copyright
Copyright © Astronomical Society of Australia 1998

Footnotes

*

Based on data from the ESA Hipparcos astrometry satellite.

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