KW Sagittarii
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Sagittarius |
| Right ascension | Template:RA[1] |
| Declination | Template:DEC[1] |
| Apparent magnitude (V) | 11.0[2] |
| Characteristics | |
| Spectral type | M1.5Iab[3] (M0I - M4Ia[4]) |
| Apparent magnitude (K) | 1.43[2] |
| U−B Template:Engvar | 3.21[3] |
| B−V Template:Engvar | 2.47[3] |
| V−R Template:Engvar | 2.58[3] |
| J−K Template:Engvar | 1.56[3] |
| Variable type | SRc[4] |
| Astrometry | |
| Radial velocity (Rv) | −7.40[5] km/s |
| Proper motion (μ) | RA: +0.843 mas/yr[1] Dec.: Script error: No such module "val". mas/yr[1] |
| Parallax (π) | 0.4355±0.0726 mas[1] |
| Distance | 7,890 ly (2,420 pc)[6]Template:Efn |
| Absolute magnitude (MV) | −7.7[7] |
| Details | |
| Mass | 20 (or 20–40Template:Efn)[3] Template:Solar mass |
| Radius | Script error: No such module "val".[3] Template:Solar radius |
| Luminosity (bolometric) | Script error: No such module "val".[3] Template:Solar luminosity |
| Surface gravity (log g) | 0.0[3] cgs |
| Temperature | Script error: No such module "val".[3] K |
| Metallicity [Fe/H] | {{{metal_fe2}}} dex |
| Other designations | |
| KW Sgr, CD−27°12032, HD 316496, HIP 87433, AAVSO 1745-28, Gaia DR2Script error: No such module "String".4063462206570029312, Gaia DR3Script error: No such module "String".4063462206570029312 | |
| Database references | |
| SIMBAD | data |
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KW Sagittarii is a red supergiant star, located approximately Script error: No such module "convert". away from the Sun in the direction of the constellation Sagittarius. It is one of the largest known stars, with a diameter about 1,000 times larger than the Sun. If placed at the center of the Solar System, the star's surface would engulf Mars, coming close to Jupiter's orbit.
Variability
In 1942, Henrietta Hill Swope listed KW Sagittarii as a variable star.[8] It varies erratically in brightness over a range of about two magnitudes.[9] It is classified as a semiregular variable,[4] although the listed period of 670 days is poorly defined.[9] The peculiar cool spectrum has led to comparisons with symbiotic variables, but it is no longer considered to be a cataclysmic binary.[10]
Distance
A distance of 2,420 parsecs is based on the assumption of membership on the Sagittarius OB5 association.[6] 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.[11] The Gaia Data Release 2 parallax is Script error: No such module "val". and implies a distance of around Script error: No such module "val".. The Gaia result carries a significant statistical margin of error, as well as an indicator that the astrometric excess noise is far beyond acceptable levels so that the parallax should be considered unreliable.[12] A 2021 study published a photogeometric distance of 2,159 pc to KW Sgr, using a parallax published by Gaia DR3 (the successor of Gaia DR2).[13]
Characteristics
KW Sagittarii is classed as a luminous cool supergiant and varies its spectral type between M0 and M4.[4] A 2005 study led by Levesque, using a MARCS model, calculated a high luminosity of Template:Solar luminosity for KW Sgr and consequently very large radius of Template:Solar radius based on the assumption of an effective temperature of Script error: No such module "val". at a distance of Script error: No such module "val".. The star was then described as among the four largest and most luminous galactic red supergiants, which includes V354 Cephei, KY Cygni and Mu Cephei.[14]
More recently, KW Sagittarii was calculated to have a lower bolometric luminosity around Template:Solar luminosity and a radius around Template:Solar radius was based on the measured angular diameter and luminosity.[3][15]
See also
- VX Sagittarii — another red supergiant (RSG) in the constellation Sagittarius
- UY Scuti
- AH Scorpii
Notes
References
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- ↑ a b c d Template:Cite DR3
- ↑ a b Script error: No such module "Citation/CS1".
- ↑ a b c d e f g h i j k Script error: No such module "Citation/CS1".
- ↑ a b c d KW Sgr, database entry, The combined table of GCVS Vols I-III and NL 67-78 with improved coordinates, General Catalogue of Variable Stars Template:Webarchive, Sternberg Astronomical Institute, Moscow, Russia. Accessed on line November 10, 2010. (Quick look: KW+Sgr)
- ↑ Script error: No such module "Citation/CS1".
- ↑ a b Script error: No such module "Citation/CS1".
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- ↑ a b Script error: No such module "Citation/CS1".
- ↑ Script error: No such module "Citation/CS1".
- ↑ Script error: No such module "Citation/CS1".
- ↑ Template:Cite DR2
- ↑ Script error: No such module "Citation/CS1". Data about this star can be seen here.
- ↑ Script error: No such module "Citation/CS1".
- ↑ Script error: No such module "Citation/CS1".
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