21 Cancri
21 Cancri is a double star in the northern zodiac constellation of Cancer. It is just visible to the naked eye as a dim, red-hued star with an apparent visual magnitude of 6.08.[2] The star is located around 820 light years away from the Sun, based on parallax. It is moving further from the Earth with a heliocentric radial velocity of 35 km/s.[6]
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Cancer |
| Right ascension | 08h 23m 55.20938s[1] |
| Declination | +10° 37′ 55.4040″[1] |
| Apparent magnitude (V) | 6.08[2] |
| Characteristics | |
| Evolutionary stage | M2III[3] |
| B−V color index | 1.507±0.004[4] |
| Variable type | suspected[5] |
| Astrometry | |
| Radial velocity (Rv) | 34.65[6] km/s |
| Proper motion (μ) | RA: −0.730[6] mas/yr Dec.: −23.274[6] mas/yr |
| Parallax (π) | 4.0080 ± 0.0989[6] mas |
| Distance | 810 ± 20 ly (250 ± 6 pc) |
| Details | |
| Radius | 53[6] R☉ |
| Luminosity | 587[6] L☉ |
| Temperature | 3,885[6] K |
| Other designations | |
| Database references | |
| SIMBAD | data |
The brighter component is an aging red giant with a stellar classification of M2III.[3] It is currently on the asymptotic giant branch, indicating this is a highly evolved star that has exhausted both its core hydrogen and core helium.[7] This is a suspected variable star.[5] It has expanded to 53[6] times the radius of the Sun and is radiating 587[6] times the Sun's luminosity from its swollen photosphere at an effective temperature of 3,885 K.[6] A 9th magnitude companion star is located one arc second away.[7]
References
- 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.
- Ducati, J. R. (2002). "VizieR On-line Data Catalog: Catalogue of Stellar Photometry in Johnson's 11-color system". VizieR On-line Data Catalog. Bibcode:2002yCat.2237....0D.
- Abt, H. A. (1985). "Visual multiples. VIII. 1000 MK types". The Astrophysical Journal Supplement Series. 59: 95. Bibcode:1985ApJS...59...95A. doi:10.1086/191064.
- Anderson, E.; Francis, Ch. (2012). "XHIP: An extended hipparcos compilation". Astronomy Letters. 38 (5): 331. arXiv:1108.4971. Bibcode:2012AstL...38..331A. doi:10.1134/S1063773712050015. S2CID 119257644.
- Samus, N. N.; Durlevich, O. V.; et al. (2009). "VizieR Online Data Catalog: General Catalogue of Variable Stars (Samus+ 2007-2013)". VizieR On-line Data Catalog: B/GCVS. Originally Published in: 2009yCat....102025S. 1: B/GCVS. Bibcode:2009yCat....102025S.
- 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.
- Eggen, Olin J. (1992). "Asymptotic Giant Branch Stars Near the Sun". The Astronomical Journal. 104: 275. Bibcode:1992AJ....104..275E. doi:10.1086/116239.
