A star that lies appreciably below the main sequence on the Hertzsprung–Russell diagram, and is somewhat bluer (i.e. of earlier spectral type) than a main-sequence star of the same luminosity; abbr. sd. Subdwarfs belong to Population II, being stars from the galactic halo which are passing through the solar neighbourhood. Their spectral types range from F to M and they differ from normal dwarfs in having a low abundance of heavy elements.
Subjects: Astronomy and Astrophysics.