Groombridge 1618 (BD+50 1725) is a star in the constellation Ursa Major. It is located close to Earth, at a distance of less than 16 light years. This is an orange dwarf star of spectral type K5 V.
This star was first identified as entry number 1618 in the work A Catalog of Circumpolar Stars, published posthumously by Stephen Groombridge in 1838.8 It has a high proper motion across the sky, which is normally taken as an indicator that the star is located nearby—making it an early candidate for parallax measurement of its distance. In 1884 the parallax angle was measured as 0″.322 ± 0″.023, which is larger than the modern value of 0″.205.
Groombridge 1618 has a stellar classification of K5 V, which means it is a K-type main sequence star that is generating energy by fusing hydrogen at its core. It has 67% of the mass of the Sun, 61% of the Sun's radius, but radiates only 4.6% of the Sun's energy. The effective surface temperature of the star's photosphere is about 4,000 K, giving it an orange hue.
It is a flare star with behavior similar to UV Ceti?, causing it to randomly undergo increases in luminosity. The chromosphere has been shown to be active and possesses star spots comparable to Sun spots. It has a greater luminosity than most flare stars, which are typically red dwarfs, but is less active. The level of activity suggests that this is a somewhat youthful star.
A search for an excess amount of infrared emission from this star by the Infrared Space Observatory came up negative, implying that Groombridge 1618 does not possess a debris disk (such as Vega).10 If this star does have a companion, astrometric measurements appear to place an upper bound of 3–12 times the mass of Jupiter on such a hypothetical object (for orbital periods in the range of 5–50 years).
According to Marcy & Benitz (1989), a possible periodicity of 122 days has been detected, inferring the potential presence of a massive planetary object with minimum mass 4 times that of Jupiter. This candidate planet has not been confirmed and the signal the authors had found could have been due to intrinsic stellar activity from the star's young age. If confirmed, the planet would be located at the outer edge of the star's habitable zone.
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