The classification of helium-rich hot subdwarfs^*

¹ Armagh Observatory, College Hill, Armagh BT61 9DG, Northern Ireland
² Dept. of Physics and Astronomy, Louisiana State University, Baton Rouge, Louisiana 70803, U.S.A.
³ School of Physics & Astronomy, University of St Andrews, Fife KY16 9SS, Scotland
⁴ Dr.-Remeis Sternwarte, Universität Erlangen-Nürnberg, Bamberg D96049, Germany
⁵ Landessternwarte, Königstuhl, D69117 Heidelberg, Germany
⁶ Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, U.S.A.

Send offprint request to: C.S. Jeffery

Received: 16 January 1997
Accepted: 13 February 1997

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 He ii, He i and Balmer lines, the sample clearly shows a wider range in He ii/He i 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, He i or He ii. The aim of this classification scheme is to establish reference standards which would be suitable for subsequent fine analysis.