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Star in the constellation Sagittarius From Wikipedia, the free encyclopedia
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.
| 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] |
| 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 | |
| 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.[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]
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]
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