VX Sagittarii
| Observation data Epoch J2000.0 Equinox J2000.0 (ICRS) | |
|---|---|
| Constellation | Sagittarius |
| Right ascension | 18h 08m 04.04831s |
| Declination | −22° 13′ 26.6327″ |
| Apparent magnitude (V) | 6.5 - 14.0 |
| Characteristics | |
| Evolutionary stage | OH/IR (ERSG/RHG, AGB/Super-AGB, or TŻO) |
| Spectral type | M4eIa - M10eIa |
| Apparent magnitude (U) | 11.72 |
| Apparent magnitude (B) | 9.41 |
| Apparent magnitude (V) | 6.52 |
| Apparent magnitude (I) | 2.11 |
| Apparent magnitude (J) | 1.23 |
| Apparent magnitude (H) | 0.13 |
| Apparent magnitude (K) | −0.50 |
| Apparent magnitude (L) | −1.61 |
| Variable type | SRc |
| Astrometry | |
| Radial velocity (Rv) | +6.47±3.37 km/s |
| Proper motion (μ) | RA: +0.36±0.76 mas/yr Dec.: −2.92±0.78 mas/yr |
| Parallax (π) | 0.64±0.04 mas |
| Distance | 5,100 ± 300 ly (1,560 ± 100 pc) |
| Details | |
| Mass | 10 to 12 M☉ |
| Radius | 1,360+250 −230, between 1,120 and 1,550, 1,350–1,940 (pulsation), 1,480 R☉ |
| Luminosity | 195,000±62,000 L☉ |
| Temperature | 2,900 (near min), 3,200-3,400 (near max), 2,400–3,300 K |
| Other designations | |
| VX Sgr, AAVSO 1802-22, BD−22°4575, CD−22°12589, HD 165674, HIP 88838, 2MASS J18080404-2213266 | |
| Database references | |
| SIMBAD | data |
VX Sagittarii (abbreviated to VX Sgr) is a luminous cool OH/IR pulsating variable star with an unusually large magnitude range located in the constellation of Sagittarius and more than one kiloparsec away from the Sun. Although it is often treated as an unusually cool red supergiant (or hypergiant), it may be instead either an extremely large asymptotic giant branch star or a possible but unlikely Thorne–Żytkow object. Nonetheless, it is one of the largest stars discovered and also one of the most luminous and massive cool stars in the Milky Way, with a radius pulsating between 1,350 and 1,940 solar radii (940,000,000 and 1.35×109 km; 6.3 and 9.0 au).
Assuming it is an AGB star, VX Sgr would be the most luminous known of its kind, exceeding the theoretical limit for the bolometric magnitude at −8.0.