2 Pegasi

2 Pegasi is a single[9] star in the constellation Pegasus, located approximately 394 light years away from the Sun based on parallax.[1] It is visible to the naked eye as a faint, red-hued star with an apparent visual magnitude of 4.52.[2] The object is moving closer to the Earth with a heliocentric radial velocity of −19 km/s.[6] It has a magnitude 12.7 visual companion, designated component B, at an angular separation of 30.4″.[10]

2 Pegasi
Location of 2 Pegasi (circled)
Observation data
Epoch J2000      Equinox J2000
Constellation Pegasus
Right ascension  21h 29m 56.89545s[1]
Declination 23° 38′ 19.8170″[1]
Apparent magnitude (V) 4.52[2]
Characteristics
Evolutionary stage AGB[3]
Spectral type M1+III[4]
U−B color index +1.93[5]
B−V color index +1.62[5]
Astrometry
Radial velocity (Rv)−18.92[6] km/s
Proper motion (μ) RA: +24.74[1] mas/yr
Dec.: +3.63[1] mas/yr
Parallax (π)8.28 ± 0.18[1] mas
Distance394 ± 9 ly
(121 ± 3 pc)
Absolute magnitude (MV)−0.89[2]
Details
Radius55[7] R☉
Luminosity653[7] L☉
Temperature3,919[7] K
Other designations
2 Peg, NSV 25624, BD+23°4325, FK5 1565, GC 30109, HD 204724, HIP 106140, HR 8225, SAO 89752, CCDM J21299+2338A, WDS J21299+2338A[8]
Database references
SIMBADdata

This is an aging red giant star with a stellar classification of M1+III,[4] currently on the asymptotic giant branch,[3] having exhausted the hydrogen at its core and evolved away from the main sequence. The interferometry-measured angular diameter of the primary component, after correcting for limb darkening, is 4.52±0.05 mas,[11] which, at its estimated distance, equates to a physical radius of about 59 times the radius of the Sun.[12] It is radiating 653 times the luminosity of the Sun from its enlarged photosphere at an effective temperature of 3,919 K, and the radius calculated from these values is 55 R☉.[7]

References
  1. Van Leeuwen, F. (2007). "Validation of the new Hipparcos reduction". Astronomy and Astrophysics. 474 (2): 653. arXiv:0708.1752. Bibcode:2007A&A...474..653V. doi:10.1051/0004-6361:20078357. Vizier catalog entry
  2. 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. Vizier catalog entry
  3. Eggen, O. J. (1992), "Asymptotic giant branch stars near the sun", The Astronomical Journal, 104: 275, Bibcode:1992AJ....104..275E, doi:10.1086/116239.
  4. Hoffleit, D.; Warren, W. H. (1995). "VizieR Online Data Catalog: Bright Star Catalogue, 5th Revised Ed. (Hoffleit+, 1991)". VizieR On-line Data Catalog: V/50. Originally Published in: 1964BS....C......0H. 5050. Bibcode:1995yCat.5050....0H.
  5. Mallama, A. (2014). "Sloan Magnitudes for the Brightest Stars". The Journal of the American Association of Variable Star Observers. 42: 443. Bibcode:2014JAVSO..42..443M.Vizier catalog entry
  6. Famaey, B.; Pourbaix, D.; Frankowski, A.; Van Eck, S.; Mayor, M.; Udry, S.; Jorissen, A. (2009). "Spectroscopic binaries among Hipparcos M giants". Astronomy and Astrophysics. 498 (2): 627. arXiv:0901.0934. Bibcode:2009A&A...498..627F. doi:10.1051/0004-6361/200810698.
  7. 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.
  8. "2 Peg". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2019-04-07.
  9. Eggleton, P. P.; Tokovinin, A. A. (September 2008). "A catalogue of multiplicity among bright stellar systems". Monthly Notices of the Royal Astronomical Society. 389 (2): 869–879. arXiv:0806.2878. Bibcode:2008MNRAS.389..869E. doi:10.1111/j.1365-2966.2008.13596.x.
  10. Mason, Brian D.; Wycoff, Gary L.; Hartkopf, William I.; Douglass, Geoffrey G.; Worley, Charles E. (2001). "The 2001 US Naval Observatory Double Star CD-ROM. I. The Washington Double Star Catalog". The Astronomical Journal. 122 (6): 3466. Bibcode:2001AJ....122.3466M. doi:10.1086/323920. Vizier catalog entry
  11. Richichi, A.; Percheron, I.; Khristoforova, M. (February 2005), "CHARM2: An updated Catalog of High Angular Resolution Measurements", Astronomy and Astrophysics, 431: 773–777, Bibcode:2005A&A...431..773R, doi:10.1051/0004-6361:20042039
  12. Lang, Kenneth R. (2006), Astrophysical formulae, Astronomy and astrophysics library, 1 (3rd ed.), Birkhäuser, ISBN 3-540-29692-1. The radius (R*) is given by:
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