  Ross 154 Location of Ross 154 in the constellationSagittarius | |
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Sagittarius |
| Right ascension | 18h 49m 49.36378s[1] |
| Declination | –23° 50′ 10.4474″[1] |
| Apparent magnitude (V) | 10.44[2] |
| Characteristics | |
| Spectral type | M3.5V[2] |
| B−Vcolor index | 1.76[3] |
| Variable type | Flare star[4] |
| Astrometry | |
| Radial velocity (Rv) | −11.12±0.57[1] km/s |
| Proper motion (μ) | RA: +639.368mas/yr[1] Dec.: –193.958mas/yr[1] |
| Parallax (π) | 336.0266±0.0317 mas[1] |
| Distance | 9.7063 ± 0.0009 ly (2.9760 ± 0.0003 pc) |
| Absolute magnitude (MV) | 13.07[2] |
| Details | |
| Mass | 0.177 ± 0.004[5] M☉ |
| Radius | 0.200 ± 0.008[5] R☉ |
| Luminosity | 0.004015±0.000048[5] L☉ |
| Surface gravity (log g) | 5.00 ± 0.05[6] cgs |
| Temperature | 3,248+68 −66[5] K |
| Metallicity [Fe/H] | -0.25[7] dex |
| Rotation | 2.848 ± 0.001[8] days |
| Rotational velocity (v sin i) | 3.5 ± 1.5[7] km/s |
| Age | under 1[7] Gyr |
| Other designations | |
| CD−23° 14742,GCTP 4338,GJ 729,HIP 92403,LHS 3414, V1216 Sagittarii.[9] | |
| Database references | |
| SIMBAD | data |
Ross 154 (V1216 Sgr) is astar in the southernzodiacconstellation ofSagittarius. It has anapparent visual magnitude of 10.44,[2] making it much too faint to be seen with the naked eye. At a minimum, viewing Ross 154 requires a telescope with anaperture of6.5 cm (3 in) under ideal conditions.[10] The distance to this star can be estimated fromparallax measurements, which places it at 9.71light-years (2.98parsecs) away fromEarth.[1] It is the nearest star in the southern constellationSagittarius, and one of thenearest stars to the Sun.
This star was first catalogued by American astronomerFrank Elmore Ross in 1925, and formed part of his fourth list of new variable stars.[11] In 1926, he added it to his second list of stars showing a measurableproper motion after comparing its position with photographic plates taken earlier by fellow American astronomerE. E. Barnard.[12] A preliminaryparallax value of0.362 ± 0.006arcseconds was determined in 1937 by Walter O'Connell using photographic plates from the Yale telescope inJohannesburg,South Africa. This placed the star at the sixth position of the then-known nearby stars.[13]
Ross 154 was found to be aUV Ceti-typeflare star, with a mean time between major flares of about two days.[4] The first such flare activity was observed from Australia in 1951 when the star increased in magnitude by 0.4.[15] Typically, the star will increase by 3–4 magnitudes during a flare.[16] The strength of the star's surfacemagnetic field is an estimated2.2 ± 0.1kG.[17] Ross 154 is anX-ray source and it has been detected by several X-ray observatories. The quiescent X-ray luminosity is about9 × 1027 ergs s−1.[7] X-ray flare emission from this star has been observed byChandra observatory, with a particularly large flare emitting2.3 × 1033 erg.[7]
Astellar classification of M3.5V[2] makes this ared dwarf star that is generating energy through thenuclear fusion of hydrogen at its core. It has an estimated 18% of theSun's mass and 20% of theSun's radius,[5] but it is radiating only 0.4% of theluminosity of the Sun.[5] In contrast to the Sun where convection only occurs in the outer layers, a red dwarf with a mass this low will be entirelyconvective.[18] Based on the relatively highprojected rotation, this is probably a young star with an estimated age of less than a billion years.[7] The abundance of elements heavier than helium is about half that in the Sun.[7]
No low-mass companions have been discovered in orbit around Ross 154.[19] Nor does it display the level ofexcess infrared emission that would suggest the presence of circumstellar dust. Suchdebris disks are rare among M-type star systems older than about 10 million years, having been primarily cleared away by drag from thestellar wind.[20] Thespace velocity components of this star in thegalactic coordinate system are[U,V,W] = [–12.2, –1.0, –7.2] km s−1.[21] It has not been identified as a member of a specific stellarmoving group[22] and is orbiting through theMilky Way galaxy at a distance from the core that varies from 27.65–30.66 kly (8.48–9.40 kpc) with anorbital eccentricity of 0.052.[23] Based on its low velocity relative to the Sun, this is believed to be a young disk (Population I) star.[24] This star will make its closest approach to the Sun in about 157,000 years, when it comes within6.39 ± 0.10 ly (1.959 ± 0.031 pc).[25]
