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9 Aurigae
Multiple star system in the constellation Auriga / From Wikipedia, the free encyclopedia
9 Aurigae (9 Aur) is a star system in Auriga (constellation). It has an apparent magnitude of about 5, making it visible to the naked eye in many suburban skies.[15] Parallax estimates made by the Hipparcos spacecraft put it at about 86 light-years (26 parsecs) from the solar system,[1] although individual Gaia Data Release 3 parallaxes place all three components at 88 light years.
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It is a well-studied Gamma Doradus variable,[5] and was one of the first stars to be so-classified.[17] This star type varies in luminosity due to non-radial pulsations.[17] Its apparent magnitude varies from 4.93 to 5.03 over a period of 1.25804 days.[2] For that reason it has been given the variable star designation V398 Aurigae.[2]
9 Aurigae is a multiple star system. The naked-eye component A is a single-lined spectroscopic binary. Only the signature of an F-type main sequence star can be seen in the spectrum, but the periodic doppler shift of the absorption lines demonstrates that there is a hidden companion in a 391.7-day orbit. The gravitational interaction of the two bodies produces variations in their respective motions, which is what creates the doppler shift.[9]
Four other companions to 9 Aurigae are listed in multiple star catalogs.[18][19] The closest companion is a 12th-magnitude red dwarf 5″ away.[5] 90″ away is component C, a 9th-magnitude star with a spectral class of K5Ve,[20] which may also be a spectroscopic binary.[10] Further-separated still is a 14th-magnitude star, component D, proposed to be a more distant red giant,[21] although Gaia astrometry places it at a similar distance and with a similar proper motion.[22] The most widely-separated companion is component E, a distant unrelated star.[21][23]