HD 37124
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HD 37124 is a star in the equatorial constellation of Taurus (the Bull), positioned about a half degree to the SSW of the bright star Zeta Tauri.<ref name=Sinnott_Perryman_1997/> The apparent visual magnitude of this star is 7.68,<ref name=Anderson_Francis_2012/> which is too dim to be visible to the naked eye. It is located at a distance of 103 light years from the Sun based on parallax, but is drifting closer with a radial velocity of −23 km/s.<ref name=Anderson_Francis_2012/> Three extrasolar planets have been found to orbit the star.
The stellar classification of HD 37124 is G4IV-V, showing a spectrum with blended traits of a main sequence star and a more evolved subgiant star. It is a quiet star with a low activity index.<ref name="Goździewski_et_al_2006"/> This star is smaller than the Sun, with 81–92% of the mass of the Sun and around 92% of the Sun's radius. It is an older, thick disk<ref name=Gonzalez2009/> star with an age of around 11 billion years, and is spinning with a projected rotational velocity of 3.6 km/s.<ref name=Earle2017/> The metallicity of the star, what astronomers term the abundance of heavier elements, is much lower than in the Sun with an iron abundance of 35–41%. It is radiating 77–84% of the Sun's luminosity from its photosphere at an effective temperature of 5,763 K.
Planetary system
As of 2011, three extrasolar planets have been found to orbit the star. The first planet, HD 37124 b, was detected by the Keck observatory through the radial velocity method; its discovery was announced on 1 November 1999.<ref name="Keck"/><ref name="Vogt2000"/> HD 37124 b was discovered orbiting its parent star around the inner edge of the habitable zone, causing the planet to have a somewhat similar insolation to that of Venus. A second planet became apparent by 2003, thought to orbit in a 1940 days on an eccentric orbit,<ref name="Butler2003"/> but this was subsequently found to be unstable.<ref name="Goźdiewski2003"/> Solving this, a three-planet solution was announced in 2005:<ref name="Vogt2005"/> this contained a second planet (HD 37124 c) orbiting at the outer edge of the habitable zone with an insolation similar to that of Mars, and a third planet, (HD 37124 d). While not obviously in any orbital resonances in 2005, an updated solution announced in 2011 found planets c and d to likely be in a 2:1 resonance.<ref name="Wright2011"/>
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