HD 2638
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HD 2638 is a ternary star system<ref name=Riddle2015/> system in the equatorial constellation of Cetus. The pair have an angular separation of Template:Val along a position angle of 166.7°, as of 2015.<ref name=Riddle2015/> This is system too faint to be visible to the naked eye, having a combined apparent visual magnitude of 9.44;<ref name=Anderson2012/> a small telescope is required. The distance to this system is 179.5 light years based on parallax, and it is drifting further away with a radial velocity of +9.6 km/s.<ref name="Gaia DR2"/> The magnitude 7.76 star HD 2567 forms a common proper motion companion to this pair<ref name=Riddle2015/> at projected separation 839″.<ref name=Roberts2015/>
The HD 2638 members A and BC have a projected separation of about Template:Val and thus an orbital period of around 130 years.<ref name=Wittrock2016/> They have a combined stellar classification of K1V.<ref name=Houk1999/> The primary component is a G-type main-sequence star with a class of G8V.<ref name=Wittrock2016/> It is smaller and less massive than the Sun, and has a lower luminosity.<ref name="Bonfanti2015"/> The secondary is a binary consisting of two red dwarf stars on close orbit with combined mass less than half the mass of the primary, and a composite spectral class of M1V.<ref name=Wittrock2016/>
Planetary systemEdit
In 2005, the discovery of an extrasolar planet HD 2638 b orbiting the primary was announced by the Geneva Extrasolar Planet Search Team. The planet has a mass 0.48 times that of Jupiter and 152.6 times that of Earth.<ref name="Moutou2005"/> The planet existence was placed under doubt in 2015 due to discovered additional stellar companions.<ref name=Roberts2015/>
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