V4381 Sagittarii

V4381 Sagittarii

A light curve for V4381 Sagittarii, plotted from Hipparcos data[1]
Observation data Epoch J2000      Equinox J2000
Constellation	Sagittarius
Right ascension	18h 08m 38.58558s[2]
Declination	−21° 26′ 58.4136″[2]
Apparent magnitude (V)	6.538[3] (6.57p - 6.62p[4])
Characteristics
Evolutionary stage	Supergiant[3]
Spectral type	A2 Iab[3]
U−B color index	+0.279[3]
B−V color index	+0.856[3]
Variable type	α Cyg[4]
Distance		approx. 1,400 ly (approx. 400 pc)
Absolute magnitude (MV)	−6.6[6]
Details
Myr
BD−21°4866, 2MASS  J18083858-2126584
Database references
SIMBAD	data

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.^[8] It was first listed as VdB 113 and described as possibly associated with a loose open cluster.^[9] 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.^[10] 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.^[11]

Distance estimations

The distance to V4381 remains poorly determined as of 2021. The 2018 research based on radio interferometry has measured 2.2±0.6 milliarcseconds parallax,^[12] while Gaia Early Data Release 3, based on optical astrometry, have resulted in measured parallax 0.6273±0.0372.^[13]

References