HD 12139 is an orange-hued star in the northern zodiac constellation of Aries. With an apparent visual magnitude of 5.89, it is a dim star that is just visible to the naked eye under good viewing conditions. It is located approximately 351 light-years (107.5 pc) distant from the Sun, based on parallax,[2] but is drifting closer with a radial velocity of −2 km/s.[1] With high probability, it is considered a member of the Hercules stream.[6]

This object is an aging red giant[7] with a stellar classification of K0III-IV,[3] meaning that it has used up its core hydrogen and is expanding. At present it has 11[1] times the girth of the Sun. The star is about two[4] billion years old with 1.7[4] times the mass of the Sun. It is radiating 58[1] times the luminosity of the Sun from its photosphere at an effective temperature of 4,780 K.[1]

A magnitude 9.36 companion is located at an angular separation of 199.70″ from the primary along a position angle of 9°, as of 2015. It is unclear if the two are physically associated.[8]

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