Ross 154

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Ross 154
Observation data
Epoch J2000      Equinox J2000
Constellation Sagittarius
Right ascension 18h 49m 49.36216s[1]
Declination –23° 50′ 10.4291″[1]
Apparent magnitude (V) 10.44[2]
Characteristics
Spectral type M3.5V[2]
B−V color index 1.76[3]
Variable type Flare star[4]
Astrometry
Radial velocity (Rv) –10.7[5] km/s
Proper motion (μ) RA: +637.02[1] mas/yr
Dec.: –191.64[1] mas/yr
Parallax (π) 336.72 ± 2.03[1] mas
Distance 9.69 ± 0.06 ly
(2.97 ± 0.02 pc)
Absolute magnitude (MV) 13.07[2]
Details
Mass 0.17[2] M☉
Radius 0.24[6] R☉
Luminosity 0.0038[7] L☉
Temperature 3,105[6] K
Metallicity [Fe/H] -0.25[8] dex
Rotational velocity (v sin i) 3.5 ± 1.5[8] km/s
Age under 1[8] Gyr
Other designations
AC-24 2833-183, GCTP 4338, GJ 729, HIP 92403, LHS 3414, V1216 Sagittarii.[9]

Ross 154 (V1216 Sgr) is a star in the southern zodiac constellation of Sagittarius. It has an apparent 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 an aperture of 6.5 cm (3 in) under ideal conditions.[10] The distance to this star can be estimated from parallax measurements, which places it at 9.69 light-years (2.97 parsecs) away from Earth.[1] It is the nearest star in the southern constellation Sagittarius, and one of the closest to the Sun. Its nearest neighbor is Barnard's star, located 1.66 pc (5.41 ly) away.

This star was first catalogued by American astronomer Frank 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 measurable proper motion after comparing its position with photographic plates taken earlier by fellow American astronomer E. E. Barnard.[12] A preliminary parallax value of 0.362 ± 0.006 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.[13]

Ross 154 was found to be a UV Ceti-type flare 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 increase in magnitude by 0.4.[14] Typically, the star will increase by 3–4 magnitudes during a flare.[15]

A stellar classification of M3.5V[2] 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[2] and is only 24% of the Sun's radius.[6] A red dwarf with a mass this low will be entirely convective, compared to the Sun where convection occurs [16] 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. The strength of the star's magnetic field is an estimated 2.6±0.3 kG.

Ross 154 is an X-ray source and it has been detected by several X-ray observatories. X-ray flare emission from this star has been observed by Chandra observatory.[8] No low-mass companions have been discovered in orbit around this star.[17]

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.[18] It has not been identified as a member of a specific stellar moving group[19] and is orbiting through the Milky Way galaxy at a distance from the core that varies from 8.478–9.400 kpc with an orbital eccentricity of 0.052.[20] Based on its low velocity relative to the Sun, this is believed to be a young disk (Population I) star.[21] This star will make its closest approach to the Sun in about 150,000 years, when it comes within 1.88 ± 0.08 pc (6.1 ± 0.26 ly).[22]

[edit] See also

[edit] References

  1. ^ a b c d e f van Leeuwen, F. (November 2007), "Validation of the new Hipparcos reduction", Astronomy and Astrophysics 474 (2): 653–664, Bibcode 2007A&A...474..653V, doi:10.1051/0004-6361:20078357 
  2. ^ a b c d e f g Staff (January 1, 2008), The One Hundred Nearest Star Systems, Research Consortium on Nearby Stars, http://www.chara.gsu.edu/RECONS/TOP100.posted.htm, retrieved 2008-06-12 
  3. ^ Corben, P. M. et al. (1972), "U, B, V photometry of 500 southern stars", Monthly Notes of the Astronomical Society of South Africa 31: 7–22, Bibcode 1972MNSSA..31....8C 
  4. ^ a b Jarrett, A. H.; Grabner, G. (1976), "On the Period Between Flares of V1216 Sagittarii", Information Bulletin on Variable Stars (1221): 1, Bibcode 1976IBVS.1221....1J 
  5. ^ Gontcharov, G. A. (2006), Pulkovo Compilation of Radial Velocities for 35493 Hipparcos Stars, http://cdsarc.u-strasbg.fr/viz-bin/Cat?cat=III%2F252&, retrieved 2010-04-18 
  6. ^ a b c Johnson, H. M.; Wright, C. D. (1983), "Predicted infrared brightness of stars within 25 parsecs of the sun", Astrophysical Journal Supplement Series 53: 643–711, Bibcode 1983ApJS...53..643J, doi:10.1086/190905 —see p. 693.
  7. ^ Pettersen, B. R. (1980), "Physical parameters of solar neighbourhood flare stars", Astronomy and Astrophysics 82 (1–2): 53–60, Bibcode 1980A&A....82...53P 
  8. ^ a b c d Wargelin, B. J. et al. (2008), "X-Ray Flaring on the dMe Star, Ross 154", The Astrophysical Journal 676 (1): 610–627, Bibcode 2008ApJ...676..610W, doi:10.1086/528702 
  9. ^ "V* V1216 Sgr -- Flare Star", SIMBAD (Centre de Données astronomiques de Strasbourg), http://simbad.u-strasbg.fr/simbad/sim-basic?Ident=V1216+Sgr, retrieved 2008-06-12 
  10. ^ Mills, H. Robert (1994), Practical Astronomy: A User-friendly, Horwood Publishing, pp. 199, ISBN 1898563020 
  11. ^ Ross, Frank E. (1926), "New variable stars, (fourth list)", Astronomical Journal 37: 91, Bibcode 1927AJ.....37...91R, doi:10.1086/104790 
  12. ^ Ross, Frank E. (February 1926), "New proper-motion stars, (second list)", Astronomical Journal 36 (856): 124–128, Bibcode 1926AJ.....36..124R, doi:10.1086/104699 
  13. ^ O'Connell, Walter (February 1938), "A faint star of large parallax", Astronomical Journal 46 (1078): 204, Bibcode 1938AJ.....46..204O, doi:10.1086/105447 
  14. ^ Mayall, Margaret W. (February 1953), "Variable Star Notes", Journal of the Royal Astronomical Society of Canada 47: 23–28, Bibcode 1953JRASC..47...23M 
  15. ^ Costa, R.; Cristaldi, S.; Rodono, M. (1970), "Cooperative Observations of the Flare Star V1216 Sgr", Information Bulletin on Variable Stars 461: 1–4, Bibcode 1970IBVS..461....1C 
  16. ^ Reiners, A.; Basri, G. (March 2009), "On the magnetic topology of partially and fully convective stars", Astronomy and Astrophysics 496 (3): 787–790, Bibcode 2009A&A...496..787R, doi:10.1051/0004-6361:200811450 
  17. ^ Hinz, Joannah L. et al. (2002), "A Near-Infrared Wide-Field Proper Motion Search for Brown Dwarfs", The Astronomical Journal 123 (4): 2027–2032, arXiv:astro-ph/0201140, Bibcode 2002AJ....123.2027H, doi:10.1086/339555 
  18. ^ "Annotations on V* V1216 Sgr object". SIMBAD. http://cdsannotations.u-strasbg.fr/annotations/simbadObject/2523169. Retrieved 2010-04-18. 
  19. ^ Montes, D. et al. (2001), "Late-type members of young stellar kinematic groups - I. Single stars", Monthly Notices of the Royal Astronomical Society 328 (1): 45–63, arXiv:astro-ph/0106537, Bibcode 2001MNRAS.328...45M, doi:10.1046/j.1365-8711.2001.04781.x 
  20. ^ Allen, C.; Herrera, M. A. (1998), "The galactic orbits of nearby UV Ceti stars", Revista Mexicana de Astronomia y Astrofisica 34: 37–46, Bibcode 1998larm.confE.115A 
  21. ^ Veeder, G. J. (1974), "Old disk flare stars", Astronomical Journal 79: 702–704, Bibcode 1974AJ.....79..702V, doi:10.1086/111600 
  22. ^ García-Sánchez, J. et al. (2001), "Stellar encounters with the solar system", Astronomy and Astrophysics 379 (2): 634–659, Bibcode 2001A&A...379..634G, doi:10.1051/0004-6361:20011330 

[edit] External links

Coordinates: Sky map 18h 49m 49.3625s, +23° 50′ 10.437″

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