HD 202951
Star in the constellation Equuleus
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HD 202951 is a probable binary star system located in the northern constellation of Equuleus. It is near the lower limit of visibility to the naked eye, having an apparent visual magnitude of 5.97.[1] The distance to this system can be estimated from the annual parallax shift of 3.34 mas,[2] yielding a value of roughly 980 light years. It is moving closer with a heliocentric radial velocity of −37 km/s.[4]
Griffin (2012) found this to be a single-lined spectroscopic binary system with an orbital period of 2.7373 ± 0.0066 yr and an eccentricity of 0.23. The a sin i value for the primary component is 54.8 ± 1.1 Gm (0.366 ± 0.007 AU), where a is the semimajor axis and i is the (unknown) orbital inclination. This value provides a lower bound for the actual semimajor axis.[5]
The visible component is an evolved K-type giant star with a stellar classification of K5 III.[1] It is a candidate variable star of unknown type, showing an amplitude variation of 0.0115 magnitude with a frequency of 0.47645 times per day, or one cycle per 2.1 days.[11] X-ray emission has been detected from this system.[12]