A&AS Supplement Series, Vol. 125, November I 1997, 501-510

Received January 16; accepted February 13, 1997

The classification of helium-rich hot subdwarfs

C.S. Jeffery - J.S. Drilling - P.M. Harrison - U. Heber - S. Moehler

Send offprint request: C.S. Jeffery
  Armagh Observatory, College Hill, Armagh BT61 9DG, Northern Ireland
  Dept. of Physics and Astronomy, Louisiana State University, Baton Rouge, Louisiana 70803, U.S.A.
  School of Physics & Astronomy, University of St Andrews, Fife KY16 9SS, Scotland
  Dr.-Remeis Sternwarte, Universität Erlangen-Nürnberg, Bamberg D96049, Germany
  Landessternwarte, Königstuhl, D69117 Heidelberg, Germany
  Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, U.S.A.

Abstract:

Spectroscopy has been obtained of 23 subluminous stars, twenty of which had been classified as "helium-rich subdwarf B stars'' from 10 Å resolution spectra. From inspection of the HeII, HeI and Balmer lines, the sample clearly shows a wider range in HeII/HeI and He/H ratios than hitherto supposed for the class. We introduce a classification scheme for helium-rich hot subdwarfs based on 1.5 Å spectra of high S/N, which can be extended to include all hot subdwarfs with spectra dominated by H, HeI or HeII. The aim of this classification scheme is to establish reference standards which would be suitable for subsequent fine analysis.

keywords: stars: fundamental parameters -- stars: subdwarfs

• 1. Introduction
• 2. Observations
• 3. Classification of 10 Å spectra
• 4. The need for a 1.5 Å classification
• 5. Classification of 1.5 Å spectra
• 6. Future work
• References