Knowra Subdwarf Subdwarf A subdwarf is a star less luminous than a main-sequence star of the same spectral type. Many subdwarfs have low abundances of elements heavier than helium and belong to the Galaxy’s older stellar populations.
Stellar classification : A system for grouping stars by properties such as temperature, luminosity, and spectral features. Subdwarfs are identified by comparing their luminosities with stars of the same spectral type.
Opacity : A measure of how strongly matter absorbs or scatters radiation passing through it. Low metal abundance changes opacity and therefore a star’s internal energy transport.
Subdwarf B star : A hot, compact star with a spectrum resembling a B-type star and a helium-burning core or shell. This well-studied class is much hotter and more compact than ordinary cool subdwarfs.
Ejnar Hertzsprung : A Danish astronomer who helped establish the relationship between stellar spectra and luminosity. His work helped distinguish stars of similar spectral type by luminosity.
Red dwarf : A small, cool, low-mass main-sequence star that emits most of its light at red and infrared wavelengths. A red dwarf is faint chiefly because it is cool and low-mass, not necessarily metal-poor.
Hertzsprung–Russell diagram : A plot that relates stars’ luminosities to their surface temperatures or spectral types. It places subdwarfs below the main sequence at comparable temperatures.
Stellar structure : The internal arrangement and physical state of a star, including its core, envelope, and energy transport. Composition-dependent structure shapes the luminosity of a subdwarf.
Subdwarf O star : A hot subdwarf whose spectrum resembles that of an O-type star. It represents the hotter spectral class among compact subdwarf populations.
Henry Norris Russell : An American astronomer who developed a diagram relating stellar spectral types to luminosities. His diagram made the subdwarf position below the main sequence visible.
White dwarf : A compact stellar remnant supported against gravity by electron degeneracy pressure. White dwarfs are faint because they are cooling remnants, unlike hydrogen-burning subdwarfs.
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