KW Sagittarii is a red supergiant star, located approximately 2,420 parsecs (7,900 light-years) 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.
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Sagittarius |
| Right ascension | 17h 52m 00.72695s[1] |
| Declination | −28° 01′ 20.5557″[1] |
| Apparent magnitude (V) | 11.0[2] |
| Characteristics | |
| Spectral type | M1.5Iab[3] (M0I - M4Ia[4]) |
| Apparent magnitude (K) | 1.43[2] |
| U−B color index | 3.21[3] |
| B−V color index | 2.47[3] |
| V−R color index | 2.58[3] |
| J−K color index | 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.: −0.946 mas/yr[1] |
| Parallax (π) | 0.4355 ± 0.0726 mas[1] |
| Distance | 7,890 ly (2,420 pc)[6][a] |
| Absolute magnitude (MV) | −7.7[7] |
| Details | |
| Mass | 20 (or 20–40[b])[3] M☉ |
| Radius | 1,009±142[3] R☉ |
| Luminosity (bolometric) | 175,000±52,000[3] L☉ |
| Surface gravity (log g) | 0.0[3] cgs |
| Temperature | 3,720±183[3] K |
| Other designations | |
| Database references | |
| SIMBAD | data |
Variability
edit
KW Sagittarii was discovered to be variable in 1928 from a study of photographic plates.[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
editA 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 0.5281±0.1392 mas and implies a distance of around 1,900 pc. 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
editKW 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 363,000 L☉ for KW Sgr and consequently very large radius of 1,460 R☉ based on the assumption of an effective temperature of 3,700 K at a distance of 3,000 pc. 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 200,000 L☉ and a radius around 1,009 ± 142 R☉ was based on the measured angular diameter and luminosity.[3][15]
See also
edit- VX Sagittarii — another red supergiant (RSG) in the constellation Sagittarius
- UY Scuti
- AH Scorpii
Notes
editReferences
edit- ^ a b c d Vallenari, A.; et al. (Gaia collaboration) (2023). "Gaia Data Release 3. Summary of the content and survey properties". Astronomy and Astrophysics. 674: A1. arXiv:2208.00211. Bibcode:2023A&A...674A...1G. doi:10.1051/0004-6361/202243940. S2CID 244398875. Gaia DR3 record for this source at VizieR.
- ^ a b Ducati, J. R. (2002). "VizieR Online Data Catalog: Catalogue of Stellar Photometry in Johnson's 11-color system". CDS/ADC Collection of Electronic Catalogues. 2237. Bibcode:2002yCat.2237....0D.
- ^ a b c d e f g h i j k Arroyo-Torres, B.; Wittkowski, M.; Marcaide, J. M.; Hauschildt, P. H. (2013). "The atmospheric structure and fundamental parameters of the red supergiants AH Scorpii, UY Scuti, and KW Sagittarii". Astronomy & Astrophysics. 554: A76. arXiv:1305.6179. Bibcode:2013A&A...554A..76A. doi:10.1051/0004-6361/201220920. S2CID 73575062.
- ^ 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 Archived 2017-06-20 at the Wayback Machine, Sternberg Astronomical Institute, Moscow, Russia. Accessed on line November 10, 2010. (Quick look: KW+Sgr)
- ^ Barbier-Brossat, M.; Petit, M.; Figon, P. (1994). "Third bibliographic catalogue of stellar radial velocities (Text in French)". Astronomy and Astrophysics Supplement Series. 108: 603. Bibcode:1994A&AS..108..603B.
- ^ a b Melnik, A. M.; Dambis, A. K. (2020). "Distance scale for high-luminosity stars in OB associations and in field with Gaia DR2. Spurious systematic motions". Astrophysics and Space Science. 365 (7): 112. arXiv:2006.14649. Bibcode:2020Ap&SS.365..112M. doi:10.1007/s10509-020-03827-0. S2CID 220128144.
- ^ Massey, Philip; Silva, David R.; Levesque, Emily M.; Plez, Bertrand; Olsen, Knut A. G.; Clayton, Geoffrey C.; Meynet, Georges; Maeder, Andre (2009). "Red Supergiants in the Andromeda Galaxy (M31)". The Astrophysical Journal. 703 (1): 420. arXiv:0907.3767. Bibcode:2009ApJ...703..420M. doi:10.1088/0004-637X/703/1/420. S2CID 119293010.
- ^ Woods, Ida E. (1928). "Tenth Magnitude Nova in Sagittarius". Harvard College Observatory Bulletin. 861: 5. Bibcode:1928BHarO.861....5W.
- ^ a b Swope, Henrietta Hill (1942). "Variable stars in MWF 189". Annals of Harvard College Observatory. 109: 1. Bibcode:1942AnHar.109....1S.
- ^ Downes, Ronald A.; Webbink, Ronald F.; Shara, Michael M.; Ritter, Hans; Kolb, Ulrich; Duerbeck, Hilmar W. (2001). "A Catalog and Atlas of Cataclysmic Variables: The Living Edition". Publications of the Astronomical Society of the Pacific. 113 (784): 764. arXiv:astro-ph/0102302. Bibcode:2001PASP..113..764D. doi:10.1086/320802. S2CID 16285959.
- ^ Van Leeuwen, F. (2007). "Validation of the new Hipparcos reduction". Astronomy and Astrophysics. 474 (2): 653–664. arXiv:0708.1752. Bibcode:2007A&A...474..653V. doi:10.1051/0004-6361:20078357. S2CID 18759600.
- ^ Brown, A. G. A.; et al. (Gaia collaboration) (August 2018). "Gaia Data Release 2: Summary of the contents and survey properties". Astronomy & Astrophysics. 616. A1. arXiv:1804.09365. Bibcode:2018A&A...616A...1G. doi:10.1051/0004-6361/201833051. Gaia DR2 record for this source at VizieR.
- ^ Bailer-Jones, C. A. L.; Rybizki, J.; Fouesneau, M.; Demleitner, M.; Andrae, R. (2021-03-01). "Estimating distances from parallaxes. V: Geometric and photogeometric distances to 1.47 billion stars in Gaia Early Data Release 3". The Astronomical Journal. 161 (3): 147. arXiv:2012.05220. Bibcode:2021AJ....161..147B. doi:10.3847/1538-3881/abd806. ISSN 0004-6256. Data about this star can be seen here.
- ^ Levesque, E. M.; Massey, P.; Olsen, K. A. G.; Plez, B.; Josselin, E.; Maeder, A.; Meynet, G. (2005). "The Effective Temperature Scale of Galactic Red Supergiants: Cool, but Not as Cool as We Thought". The Astrophysical Journal. 628 (2): 973–985. arXiv:astro-ph/0504337. Bibcode:2005ApJ...628..973L. doi:10.1086/430901. S2CID 15109583.
- ^ Mauron, N.; Josselin, E. (2011). "The mass-loss rates of red supergiants and the de Jager prescription". Astronomy and Astrophysics. 526: A156. arXiv:1010.5369. Bibcode:2011A&A...526A.156M. doi:10.1051/0004-6361/201013993. S2CID 119276502.