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Reference.org
Subdwarf O star
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<p>A subdwarf O star (sdO) is a type of hot, but low-mass star. O-type <a href="/facts/Subdwarf/5h8hyTHM">subdwarfs</a> are much dimmer than regular <a href="/facts/O-type_main-sequence_star/zdcLjAEr">O-type main-sequence stars</a>, but with a brightness about 10 to 100 times that of the Sun, and have a mass approximately half that of the Sun. Their temperature ranges from 40,000 to 100,000 K. Ionized helium is prominent in their spectra. Their surface gravity (typically given as the gravity's logarithm), log <i>g</i> is usually between 4.0 and 6.5. Many sdO stars are moving at high velocity through the <a href="/facts/Milky_Way/ulF6lccN">Milky Way</a> and are found at high <a href="/facts/Galactic_latitude/Un6BambN">galactic latitudes</a>. </p>