Ross 154 (V1216 Sgr) is a red dwarf star located around 9.69 light years (2.97 parsecs) away from Earth in the constellation of Sagittarius. It has an apparent magnitude of 10.44 which makes it too faint to be seen with the naked eye. It is the nearest star in the southern constellation of Sagittarius and one of the closest stars to the Sun.
Description[]
The star was first catalogued by the American astronomer Frank Elmore Ross in 1925. It formed part of his fourth list of new variable stars. In 1926, he added it to his second list of stars showing a measurable proper motion after comparing its position with photographic plates taken earlier by fellow American astronomer E. E. Barnard. A preliminary parallax value of 0.362 arcseconds was determined in 1937 by Walter O'Connell, using photographic plates from the Yale telescope in Johannesburg, South africa. This placed the star at the sixth position of the then-known nearby stars.
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 star a red dwarf star that is generating energy through the nuclear fusion of hydrogen at its core. It has about 17% of the Sun's mass, 24% of the Sun's radius, and 0.38% of the Sun's luminosity. 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 have been discovered in orbit around Ross 154. Nor does it display the level of excess infrared emission that would suggest the presence of circumstellar dust. Such debris disks are rare among M-type star systems older than about 10 million years, having been primarily cleared away by drag from the stellar wind. The space velocity components of this star in the galactic coordinate system are [U, V, W] = [–12.2, –1.0, –7.2] km s−1.