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 (18.104.22.168) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/551/A31
© ESO, 2013
Current usage metrics show cumulative count of Article Views (full-text article views including HTML views, PDF and ePub downloads, according to the available data) and Abstracts Views on Vision4Press platform.
Data correspond to usage on the plateform after 2015. The current usage metrics is available 48-96 hours after online publication and is updated daily on week days.
Initial download of the metrics may take a while.