VX Sagittarii

From Wikipedia, the free encyclopedia
Jump to: navigation, search
VX Sagittarii

SpaceEngine concept of how the star VX Sagittarii may appear from 2.326 Astronomical Units.
Observation data
Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation Sagittarius
Right ascension 18h 08m 04.0485s
Declination −22° 13′ 26.614″
Apparent magnitude (V) +6.9-12.7[1]
Evolutionary stage Red Hypergiant
Spectral type M4eIa-M10eIa[1]
Apparent magnitude (U) 11.72
Apparent magnitude (B) 9.41
Apparent magnitude (V) 6.52
Apparent magnitude (I) 2.11
Apparent magnitude (J) 1.23
Apparent magnitude (H) 0.13
Apparent magnitude (K) −0.50
Apparent magnitude (L) −1.61
Variable type Semi-regular
Radial velocity (Rv) +30 (variable)[2] km/s
Proper motion (μ) RA: 3.20 mas/yr
Dec.: -6.71 mas/yr
Parallax (π) 3.82 ± 2.73 mas
Distance ≈ 5.15k ly
(1.57k[3] pc)
Absolute magnitude (MV) −4.46[4]
Mass 7-11[5] M
Radius >1,520[4] R
Luminosity 340,000[4] L
Temperature 3,575[4] K
Other designations
VX Sgr, HIP 88838, BD-22 4575, CD-22 12589, HD 165674.
Database references

VX Sagittarii is a late-type red supergiant or hypergiant pulsating variable star located more than 1.5 kiloparsec away from the Sun in the constellation of Sagittarius. It is one of the largest stars discovered so far, although the radius is poorly known.a

Stellar characteristics[edit]

The star is classed as a cool semiregular variable with a pulsational period of 732 days, although the variations have an amplitude comparable to a long period variable, a spectral type varying between M4e (close to visual maximum) and M10e (at minimum light), and a luminosity class of Ia (bright supergiant). The effective temperature is also highly variable from around 2,500K at minimum to around 3,500K near maximum,[6] and with an average temperature given as 2,900 K.[7]

Stellar behaviour at times resembles that of Mira-type pulsating giants and shows hints of molecular water layers and SiO masers in the atmosphere,[8] but at other times the pulsations are smaller and irregular. VX Sgr is far more luminous than any true long period variable. Although the visual brightness variation is dramatic, the bolometric luminosity is dominated by infrared output and the variation in the infrared is small, so variation in luminosity is modest. Data in the starbox is generally given for peak luminosity and peak temperature.


  1. ^ The radius of VX Sgr varies as it pulsates and cannot accurately be measured. The given radius is an estimate assuming peak luminosity coincides with peak temperature, but peak luminosity is generally at a somewhat lower temperature in pulsating variables and so the peak radius is likely to be larger than this.


  1. ^ a b Kiss, L. L.; Szabó, G. M.; Bedding, T. R. (2006). "Variability in red supergiant stars: Pulsations, long secondary periods and convection noise". Monthly Notices of the Royal Astronomical Society 372 (4): 1721. arXiv:astro-ph/0608438. Bibcode:2006MNRAS.372.1721K. doi:10.1111/j.1365-2966.2006.10973.x. 
  2. ^ Knapp, G. R.; Sutin, B. M.; Phillips, T. G.; Ellison, B. N.; Keene, J. B.; Leighton, R. B.; Masson, C. R.; Steiger, W.; Veidt, B.; Young, K. (1989). "CO emission from evolved stars and proto-planetary nebulae". The Astrophysical Journal 336: 822. Bibcode:1989ApJ...336..822K. doi:10.1086/167052. 
  3. ^ Chen, X.; Shen, Z. Q.; Xu, Y. (2007). "Measuring the Distance of VX Sagittarii with SiO Maser Proper Motions". Chinese Journal of Astronomy and Astrophysics 7 (4): 531. doi:10.1088/1009-9271/7/4/09. 
  4. ^ a b c d Nicolas Mauron; Eric Josselin (2010). "The mass-loss rates of red supergiants and the de Jager prescription". arXiv:1010.5369v1 [astro-ph.SR]. 
  5. ^ Chiavassa; Lacour; Millour; Driebe; Wittkowski; Plez; Thiebeaut; Josselin; Freytag (2009). "VLTI/AMBER spectro-interferometric imaging of VX Sgr's inhomogenous outer atmosphere". arXiv:0911.4422 [astro-ph.SR]. 
  6. ^ Van Loon, J. T.; Cioni, M. -R. L.; Zijlstra, A. A.; Loup, C. (2005). "An empirical formula for the mass-loss rates of dust-enshrouded red supergiants and oxygen-rich Asymptotic Giant Branch stars". Astronomy and Astrophysics 438: 273. arXiv:astro-ph/0504379. Bibcode:2005A&A...438..273V. doi:10.1051/0004-6361:20042555. 
  7. ^ Lockwood, G.W.; Wing, R. F. (1982). "The light and spectrum variations of VX Sagittarii, an extremely cool supergiant". Monthly Notices of the Royal Astronomical Society 198: 385–404. Bibcode:1982MNRAS.198..385L. doi:10.1093/mnras/198.2.385. Retrieved 16 October 2013. 
  8. ^ Greenhill; et al. (1995). "The SiO Masers and Dust Shell of VX SGR". Astrophysics and Space Science 224 (1–2): 1–9. Bibcode:1995Ap&SS.224..469G. doi:10.1007/BF00667909.