Guardians of the Stars
Ross 154 (V1216 Sgr) is a star in the southern zodiac constellation of Sagittarius. It has an apparent visual magnitude of 10.44, making it much too faint to be seen with the naked eye from Earth. The distance to this star is 9.69 light-years (2.97 parsecs) away from Earth. It is the nearest star in the southern constellation Sagittarius, and one of the nearest stars to the Sun.
Ross 154 was found to be a UV Ceti-type flare star, with a mean time between major flares of about two days. The first such flare activity was observed from Australia in 1951 when the star increased in magnitude by 0.4. Typically, the star will increase by 3–4 magnitudes during a flare. The strength of the star’s surface magnetic field is an estimated 2.2 ± 0.1 kG. Ross 154 is an X-ray source and it has been detected by several X-ray observatories. The quiescent X-ray luminosity is about 9 × 1027 ergs s−1. X-ray flare emission from this star has been observed by Chandra observatory, with a particularly large flare emitting 2.3 × 1033 erg.
A stellar classification of M3.5V makes this a red dwarf star that is generating energy through the nuclear fusion of hydrogen at its core. It has an estimated 17% of the Sun’s mass and 24% of the Sun’s radius, but it is radiating only 0.38% of the luminosity of the Sun. In contrast to the Sun where convection only occurs in the outer layers, a red dwarf with a mass this low will be entirely convective. Based on the relatively high projected rotation, this is probably a young star with an estimated age of less than a billion years. The abundance of elements heavier than helium is about half that in the Sun.
No low-mass companions orbit around Ross 154. This system is a young disk (Population I) star, which is proven by its low velocity relative to the Sun. It has not been identified as a member of a specific stellar moving group and is orbiting through the Milky Way galaxy at a distance from the core that varies from 27.65–30.66 kly (8.48–9.40 kpc) with an orbital eccentricity of 0.052. This star will make its closest approach to the Sun in about 157,000 years, when it comes within 6.39 ± 0.10 ly (1.959 ± 0.031 pc).