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(sub-dworf ) A star that is smaller and about 1.5–2 magnitudes fainter than normal dwarf (main-sequence) stars of the same spectral type. The subdwarfs are mainly old (halo population II) objects that lie just beneath the main sequence on the Hertzsprung–Russell diagram. Their anomalous position is due to their low metal content, which affects their apparent temperature and hence their spectral type. They are usually denoted by the prefix sd , as in sdK4, or given the luminosity class VI.



a dwarf star in the halo of the Galaxy. By comparison with stars of the same mass in the main sequence of the Hertzsprung-Russell diagram, subdwarfs have a higher surface temperature and a lower metal content in their atmospheres. Subdwarfs do not obey the mass-luminosity law that holds for most stars.

The use of the term “subdwarf” is due to the circumstance that for a long time the stars of this type were believed to form in the Hertzsprung-Russell diagram a separate sequence parallel to the main sequence and lying 1.5–2 stellar magnitudes below it. In actuality, subdwarfs are for the most part main sequence stars. The displacement of subdwarfs below the main sequence was a result of a failure to correctly allow for the blanketing effect in subdwarf spectra. Subdwarfs are believed to be old stars.

References in periodicals archive ?
So, based on their movements in our galaxy, I can evaluate whether a star is an old subdwarf or not.
Hot Subdwarf Stars and Related Objects Workshop (5th: 2011: Stellenbosch, Western Cape, South Africa) Ed.
But sometimes, the giant sheds its stellar skin before contracting, leaving behind a bright, beating heart--the hot B subdwarf.
Among the topics are precision observational asteroseismology using Kepler spacecraft data, updates on the pulsating sdB star Feige 48 through spectroscopy, glimpses into the secret lives of hot subdwarf stars, tidally enhanced stellar wind in binaries as a second parameter for the horizontal branch morphology of globular clusters, hot subdwarf stars as the donors of type Ia supernova progenitors, and a radial velocity survey of hot subdwarfs with main sequence companions using the Hobby-Eberly telescope.
Our calculations show that this subdwarf travels up to 200,000 light years away from the center of the Galaxy, almost 10 times farther than the Sun," said Bochanski, a postdoctoral researcher in Burgasser's group at MIT.
The stellar classes discussed in detail at the conference include R Coronae Borealis stars, extreme helium stars, Wolf-Rayet central stars of planetary nebulae, white dwarfs, and helium-rich subdwarf O and B stars.
This extended range should permit astronomers to calibrate the brightnesses of Cepheid variable stars (used as "standard candles" for gauging the distances of other galaxies) and of relatively old subdwarf stars (allowing better distance estimates to globular clusters).
Hot Subdwarfs in Bamberg, in Hot Subdwarf Stars and Related Objects, eds.
Prof Warner attended the conference "Hot Subdwarf Stars and related Objects" in Bamberg (D) in July 2007 and gave the conference summary.
Only a few dozen ultracool subdwarfs, which are up to 10,000 times fainter than the Sun, have been identified.
V391 Pegasi belongs to a rare class of stars, called B-type subdwarfs.
c] are wonderfully curved, especially in the regions of supergiants (the lower left part of the diagram) and hot subdwarfs (the upper right part).