Volume 551, March 2013
|Number of page(s)||12|
|Published online||14 February 2013|
An MK-like system of spectral classification for hot subdwarfs⋆
1 Department of Physics and Astronomy, Louisiana State University, Baton Rouge, LA 70803, USA
2 Armagh Observatory, College Hill, Armagh BT61 9DG, Northern Ireland
3 Dr. Remeis Sternwarte, Universität Erlangen-Nürnberg, 96049 Bamberg, Germany
4 European Southern Observatory, Karl-Schwarzschild-Strasse 2, 85748 Garching, Germany
5 Centre for Astrophysics Research, University of Hertfordshire, College Lane, Hatfield AL10 9AB, UK
Received: 17 April 2012
Accepted: 27 November 2012
An MK (Morgan-Keenan)-like system of spectral classification for hot subdwarfs is presented. We find that a three-dimensional spectral type, consisting of a “spectral” class, a “luminosity” class, and a “helium” class, is necessary to classify the sdO (subdwarf O) and sdB (subdwarf B) stars. In addition, the helium-strong stars appear to form two parallel spectral sequences: one showing strong lines of CII, CIII, or CIV, and the other with these same lines weak or absent. We also give a preliminary calibration of the new spectral types in terms of effective temperature, surface gravity, and surface helium-to-hydrogen abundance ratio, and show the relation between the new spectral types and the natural groups defined by the Palomar-Green (PG) survey.
Key words: stars: early-type / subdwarfs / stars: atmospheres
The normalized, unsmoothed spectra used in this paper are available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (22.214.171.124) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/551/A31
© ESO, 2013
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