V4381 Sagittarii

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V4381 Sagittarii
Observation data
Epoch J2000      Equinox J2000
Constellation Sagittarius
Right ascension 18h 08m 38.58558s[1]
Declination −21° 26′ 58.4136″[1]
Apparent magnitude (V) 6.538[2] (6.57p - 6.62p[3])
Evolutionary stage Supergiant[2]
Spectral type A2 Iab[2]
U−B color index +0.279[2]
B−V color index +0.856[2]
Variable type α Cyg[3]
Radial velocity (Rv) −16[4] km/s
Proper motion (μ) RA: −1.65[1] mas/yr
Dec.: −1.05[1] mas/yr
Parallax (π) 2.25 ± 0.55[1] mas
Distance approx. 1,400 ly
(approx. 400 pc)
Absolute magnitude (MV) −6.6[5]
Mass 7.00[6] M
Luminosity 39,000[2] L
Surface gravity (log g) 1.50[2] cgs
Temperature 9,000[2] K
Rotational velocity (v sin i) 18[2] km/s
Age 43.3[6] Myr
Other designations
V4381 Sagittarii, HD 165784, HIP 88876, BD−21°4866, 2MASS J18083858-2126584
Database references

V4381 Sagittarii is a variable star in the constellation Sagittarius. A white supergiant of spectral type A2/A3Iab, it is an Alpha Cygni variable that varies between apparent photographic magnitudes 6.57 and 6.62. Its visual apparent magnitude is about 6.54.

V4381 Sagittarii is associated with a small reflection and emission nebula, although it is not actually seen within the nebulosity. The nebula is catalogued as GN 18.05.6.[7] It was first listed as VdB 113 and described as possibly associated with a loose open cluster.[8] That name has since been used for the cluster itself, which is much more distant than the distance of V4381 Sagittarii derived from its Hipparcos parallax.[9] The whole cluster is less than a quarter of a degree across, with dozens of members from 8th magnitude downwards. V4381 Sagittarii is listed as a probable member, while the nearby bright stars HD 165516 and WR 111 are considered unlikely to be members.[10]


  1. ^ a b c d e Van Leeuwen, F. (2007). "Validation of the new Hipparcos reduction". Astronomy and Astrophysics. 474 (2): 653. arXiv:0708.1752Freely accessible. Bibcode:2007A&A...474..653V. doi:10.1051/0004-6361:20078357. 
  2. ^ a b c d e f g h i Firnstein, M.; Przybilla, N. (2012). "Quantitative spectroscopy of Galactic BA-type supergiants. I. Atmospheric parameters". Astronomy & Astrophysics. 543: A80. arXiv:1207.0308Freely accessible. Bibcode:2012A&A...543A..80F. doi:10.1051/0004-6361/201219034. 
  3. ^ a b Samus, N. N.; Durlevich, O. V.; et al. (2009). "VizieR Online Data Catalog: General Catalogue of Variable Stars (Samus+ 2007-2013)". VizieR On-line Data Catalog: B/gcvs. Originally published in: 2009yCat....102025S. 1. Bibcode:2009yCat....102025S. 
  4. ^ Gontcharov, G. A. (2006). "Pulkovo Compilation of Radial Velocities for 35 495 Hipparcos stars in a common system". Astronomy Letters. 32 (11): 759. arXiv:1606.08053Freely accessible. Bibcode:2006AstL...32..759G. doi:10.1134/S1063773706110065. 
  5. ^ Humphreys, R. M. (1978). "Studies of luminous stars in nearby galaxies. I. Supergiants and O stars in the Milky Way". Astrophysical Journal. 38: 309. Bibcode:1978ApJS...38..309H. doi:10.1086/190559. 
  6. ^ a b Tetzlaff, N.; Neuhäuser, R.; Hohle, M. M. (2011). "A catalogue of young runaway Hipparcos stars within 3 kpc from the Sun". Monthly Notices of the Royal Astronomical Society. 410: 190. arXiv:1007.4883Freely accessible. Bibcode:2011MNRAS.410..190T. doi:10.1111/j.1365-2966.2010.17434.x. 
  7. ^ Magakian, T. Yu. (2003). "Merged catalogue of reflection nebulae". Astronomy and Astrophysics. 399: 141. Bibcode:2003A&A...399..141M. doi:10.1051/0004-6361:20021743. 
  8. ^ Van Den Bergh, S. (1966). "A study of reflection nebulae". Astronomical Journal. 71: 990. Bibcode:1966AJ.....71..990V. doi:10.1086/109995. 
  9. ^ Piskunov, A. E.; Schilbach, E.; Kharchenko, N. V.; Röser, S.; Scholz, R.-D. (2008). "Tidal radii and masses of open clusters". Astronomy and Astrophysics. 477: 165. Bibcode:2008A&A...477..165P. doi:10.1051/0004-6361:20078525. 
  10. ^ Kharchenko, N. V.; Piskunov, A. E.; Schilbach, E.; Röser, S.; Scholz, R.-D. (2013). "Global survey of star clusters in the Milky Way. II. The catalogue of basic parameters". Astronomy & Astrophysics. 558: A53. arXiv:1308.5822Freely accessible. Bibcode:2013A&A...558A..53K. doi:10.1051/0004-6361/201322302. 

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