V4381 Sagittarii
Star in the constellation Sagittarius
From Wikipedia, the free encyclopedia
V4381 Sagittarii is a star in the constellation Sagittarius. It was discovered to be a variable star in 1996, when the Hipparcos data was analysed.[8] 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.
| Observation data Epoch J2000 Equinox ICRS | |
|---|---|
| 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] |
| Astrometry | |
| Radial velocity (Rv) | −16[5] km/s |
| Proper motion (μ) | RA: −1.65[2] mas/yr Dec.: −1.05[2] mas/yr |
| Parallax (π) | 2.25±0.55 mas[2] |
| Distance | approx. 1,400 ly (approx. 400 pc) |
| Absolute magnitude (MV) | −6.6[6] |
| Details | |
| Mass | 7.00[7] M☉ |
| Luminosity | 39,000[3] L☉ |
| Surface gravity (log g) | 1.50[3] cgs |
| Temperature | 9,000[3] K |
| Rotational velocity (v sin i) | 18[3] km/s |
| Age | 43.3[7] Myr |
| Other designations | |
| V4381 Sagittarii, HD 165784, HIP 88876, BD−21°4866, 2MASS J18083858-2126584 | |
| Database references | |
| SIMBAD | data |
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.[9] It was first listed as VdB 113 and described as possibly associated with a loose open cluster.[10] 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.[11] 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.[12]