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Subdwarf
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<a href="/facts/Hertzsprung%25E2%2580%2593Russell_diagram/53YWnCvR">Hertzsprung–Russell diagram</a> <a href="/facts/Stellar_classification/dYrIuK9H">Spectral type</a> <a href="/facts/O-class_star/dYrIuK9H">O</a> <a href="/facts/B-class_star/dYrIuK9H">B</a> <a href="/facts/A-class_star/dYrIuK9H">A</a> <a href="/facts/F-class_star/dYrIuK9H">F</a> <a href="/facts/G-class_star/dYrIuK9H">G</a> <a href="/facts/K-class_star/dYrIuK9H">K</a> <a href="/facts/M-class_star/dYrIuK9H">M</a> <a href="/facts/L-class_star/fa7kr9lH">L</a> <a href="/facts/T-class_star/BxLocDRU">T</a> <a href="/facts/Brown_dwarf/fa7kr9lH">Brown dwarfs</a> <a href="/facts/White_dwarf/gIYlTtrC">White dwarfs</a> <a href="/facts/Red_dwarf/56CMQcF0">Red dwarfs</a> Subdwarfs <a href="/facts/Main_sequence/DJ3Wq8kd">Main sequence("dwarfs")</a> <a href="/facts/Subgiant/wD7o7E2Q">Subgiants</a> <a href="/facts/Giant_star/kMseY7qf">Giants</a> <a href="/facts/Red_giant/lla6Bsvy">Red giants</a> <a href="/facts/Blue_giant/JPjptPb7">Blue giants</a> <a href="/facts/Bright_giant/qH3X0fuw">Bright giants</a> <a href="/facts/Supergiant_star/y7w8WEcm">Supergiants</a> <a href="/facts/Red_supergiant/hPBWvABE">Red supergiant</a> <a href="/facts/Hypergiant/Q95EmMhT">Hypergiants</a> <a href="/facts/Absolute_magnitude/R8RVxkLx">absolutemagni-tude(MV)</a> <p>A subdwarf, sometimes denoted by "sd", is a star with <a href="/facts/Luminosity_class/dYrIuK9H">luminosity class</a> VI under the <a href="/facts/Stellar_classification/dYrIuK9H">Yerkes spectral classification</a> system. They are defined as <a href="/facts/Star/PFbd6ICx">stars</a> with <a href="/facts/Luminosity/1tdhpk9l">luminosity</a> 1.5 to 2 <a href="/facts/Absolute_magnitude/R8RVxkLx">magnitudes</a> lower than that of main-sequence stars of the same <a href="/facts/Spectral_type/dYrIuK9H">spectral type</a>. On a <a href="/facts/Hertzsprung%25E2%2580%2593Russell_diagram/53YWnCvR">Hertzsprung–Russell diagram</a> subdwarfs appear to lie below the <a href="/facts/Main_sequence/DJ3Wq8kd">main sequence</a>. </p><p>The term "subdwarf" was coined by <a href="/facts/Gerard_Kuiper/2VghxPem">Gerard Kuiper</a> in 1939, to refer to a series of stars with anomalous spectra that were previously labeled as "intermediate <a href="/facts/White_dwarfs/gIYlTtrC">white dwarfs</a>".(p 87) </p><p>Since <a href="/facts/Gerard_Kuiper/2VghxPem">Kuiper</a> coined the term, the subdwarf type has been extended to lower-mass stars than were known at the time. Astronomers have also discovered an entirely different group of blue-white subdwarfs, making two distinct categories: </p> <ul><li>Cool subdwarfs</li> <li>Hot subdwarfs</li></ul>