KW Sagittarii
 Location of KW Sgr |
|
| Observation data Epoch J2000.0 Equinox J2000.0 (ICRS) |
|
|---|---|
| Constellation | Sagittarius |
| Right ascension | 17h 52m 00.72665s |
| Declination | −28° 01′ 20.5622″ |
| Apparent magnitude (V) | 11.0 |
| Characteristics | |
| Spectral type | M1.5Iab(M0I - M4Ia) |
| Apparent magnitude (K) | 1.43 |
| U−B color index | 3.21 |
| B−V color index | 2.47 |
| V−R color index | 2.58 |
| J−K color index | 1.56 |
| Variable type | SRC |
| Astrometry | |
| Radial velocity (Rv) | −7.40 km/s |
| Proper motion (μ) |
RA: 0.39 mas/yr Dec.: −1.62 mas/yr |
| Parallax (π) | −2.43 ± 0.94mas |
| Distance | 7,800ly (2,400 pc) |
| Details | |
| Radius | 1,009 ± 142 R☉ |
| Luminosity (bolometric) | 176,000-360,000 L☉ |
| Surface gravity (log g) | 0.0-−0.5 cgs |
| Temperature | 3,720 ± 183 K |
| Other designations | |
| Database references | |
| SIMBAD | data |
8.5 to 11 (AAVSO)
11.0 to 13.2 (p)
KW Sagittarii is a red supergiant, located approximately 2,400 parsecs away from our Sun in the direction of the constellation Sagittarius. It has a size of 1,009 R☉ (up to 1,460 R☉ by some estimates), making it one of the largest known stars. If placed at the center of the Solar System, the star's surface would engulf Mars.
The distance of 2,400 parsecs is based on the assumption of membership on the Sagittarius OB5 association. The parallax derived from the Hipparcos mission is negative so doesn't give much information about the distance except that it is likely to be large.
Levesque calculate that the star has a bolometric luminosity of over 360,000 L☉ and a radius around 1,460 R☉ based on the assumption of an effective temperature of 3,700 K. Marcaide calculate that the star has a bolometric luminosity of less than 200,000 L☉ based on the measured flux and an assumed distance, and a radius around 1,009 ± 142 R☉ based on the measured angular diameter and luminosity. The effective temperature was then derived from the luminosity and radius.
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