HD 2638

HD 2638 is a ternary star system system in the equatorial constellation of Cetus. The pair have an angular separation of $0.886$ along a position angle of 166.7°, as of 2015. This is system too faint to be visible to the naked eye, having a combined apparent visual magnitude of 9.44; 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. The magnitude 7.76 star HD 2567 forms a common proper motion companion to this pair at projected separation 839″.

The HD 2638 members A and BC have a projected separation of about $9.576$ and thus an orbital period of around 130 years. They have a combined stellar classification of K1V. The primary component is a G-type main-sequence star with a class of G8V. It is smaller and less massive than the Sun, and has a lower luminosity. The secondary is a binary consisting of who red dwarf stars on close orbit with combined mass less than half the mass of the primary, and a composite spectral class of M1V.

Planetary system
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. The planet existence was placed under doubt in 2015 due to discovered additional stellar companions.