V4381 Sagittarii

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
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])
Characteristics
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]
Astrometry
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
Distanceapprox. 1,400 ly
(approx. 400 pc)
Absolute magnitude (MV)−6.6[5]
Details
Mass7.00[6] M☉
Luminosity39,000[2] L☉
Surface gravity (log g)1.50[2] cgs
Temperature9,000[2] K
Rotational velocity (v sin i)18[2] km/s
Age43.3[6] Myr
Other designations
V4381 Sagittarii, HD 165784, HIP 88876, BD−21°4866, 2MASS J18083858-2126584
Database references
SIMBADdata

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]

References
  1. Van Leeuwen, F. (2007). "Validation of the new Hipparcos reduction". Astronomy and Astrophysics. 474 (2): 653. arXiv:0708.1752. Bibcode:2007A&A...474..653V. doi:10.1051/0004-6361:20078357.
  2. Firnstein, M.; Przybilla, N. (2012). "Quantitative spectroscopy of Galactic BA-type supergiants. I. Atmospheric parameters". Astronomy & Astrophysics. 543: A80. arXiv:1207.0308. Bibcode:2012A&A...543A..80F. doi:10.1051/0004-6361/201219034.
  3. 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:1606.08053. 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. 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:1007.4883. 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:1308.5822. Bibcode:2013A&A...558A..53K. doi:10.1051/0004-6361/201322302.
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