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56 Pegasi

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Star in the constellation Pegasus
56 Pegasi
Location of 56 Pegasi (circled)
Observation data
Epoch J2000      Equinox J2000
Constellation Pegasus
Right ascension 23 07 06.74364
Declination 25° 28′ 05.788″
Apparent magnitude (V) 4.74
Characteristics
Spectral type K0.5II:Ba1CN-2CH-0.5 + sdO
U−B color index +1.14
B−V color index +1.32
Astrometry
Radial velocity (Rv)−27.55 km/s
Proper motion (μ) RA: −4.288 mas/yr
Dec.: −32.639 mas/yr
Parallax (π)6.1131 ± 0.4108 mas
Distance530 ± 40 ly
(160 ± 10 pc)
Absolute magnitude (MV)−1.32
Orbit
Period (P)111.140±0.14 d
Eccentricity (e)0
Periastron epoch (T)51738.8±0.5 MJD
Semi-amplitude (K1)
(primary)		1.47±0.04 km/s
Details
56 Peg A
Mass5.4 M☉
Radius41 R☉
Luminosity18.2 - 18.9 L☉
Surface gravity (log g)0.50 cgs
Temperature4,185±85 K
Metallicity −0.21 dex
Rotational velocity (v sin i)4.4 km/s
Age100±100 Myr
Other designations
56 Peg, NSV 14429, BD+24°4716, FK5 3848, GC 32201, HD 218356, HIP 114155, HR 8796, SAO 91019, 2MASS J23070675+2528055
Database references
SIMBADdata

56 Pegasi is a binary star system in the northern constellation of Pegasus. It is visible to the naked eye with a combined apparent visual magnitude of 4.74. The system is approximately 590 light years away from the Sun based on parallax, but is drifting closer with a radial velocity of −28 km/s. It is listed as a member of the Wolf 630 moving group.

The variable radial velocity of this star was announced in 1911 by W. W. Campbell. It is a single-lined spectroscopic binary in an assumed circular orbit with a period of 111.1 days. The a sin i value for this system is 0.01511 ± 0.00040 AU (2.26 ± 0.06 Gm), where a is the semimajor axis and i is the (unknown) orbital inclination. This value provides a lower bound on the true semimajor axis, which in this case is their actual separation.

The primary component is a peculiar bright giant with a stellar classification of K0.5 II: Ba1 CN-2 CH-0.5. This notation indicates it is a K-type giant with some uncertainty about the classification, along with an overabundance of barium and underabundances of the CN and CH radicals. It is an active star, roughly 100 million years old, with 5.4 times the Sun's mass. The star has expanded to 40 times the radius of the Sun and is radiating 680 times the Sun's luminosity from its enlarged photosphere at an effective temperature of 4,416 K.

The system displays an excess of ultraviolet radiation that must be coming from the secondary companion. Simon et al. (1982) classified this object as a subdwarf O star. Alternatively, it may be a white dwarf companion with an accretion disk. Several puzzling features in the evolutionary history of this pair may be explained if the primary is a fast rotator being seen nearly pole-on. The star may have been spun up during a mass transfer episode with the secondary.

References

  1. ^ 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.
  2. ^ 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.
  3. ^ Keenan, Philip C.; McNeil, Raymond C. (1989). "The Perkins catalog of revised MK types for the cooler stars". Astrophysical Journal Supplement Series. 71: 245. Bibcode:1989ApJS...71..245K. doi:10.1086/191373.
  4. ^ Simon, T.; et al. (1982). "On the reality of a boundary in the H-R diagram between late-type stars with and without high temperature outer atmospheres". Astrophysical Journal. 257: 225. Bibcode:1982ApJ...257..225S. doi:10.1086/159981.
  5. ^ Griffin, R. F. (2006). "Spectroscopic binary orbits from photoelectric radial velocities - Paper 186: 56 Pegasi". The Observatory. 126: 1. Bibcode:2006Obs...126....1G.
  6. ^ Famaey, B.; et al. (2005). "Local kinematics of K and M giants from CORAVEL/Hipparcos/Tycho-2 data". Astronomy & Astrophysics. 430: 165–186. arXiv:astro-ph/0409579. Bibcode:2005A&A...430..165F. doi:10.1051/0004-6361:20041272. S2CID 17804304.
  7. Frankowski, A.; Jorissen, A. (2006). "The puzzling case of 56 Pegasi: A fast rotator seen nearly pole-on". The Observatory. 126: 25. arXiv:astro-ph/0512036. Bibcode:2006Obs...126...25F.
  8. ^ Tetzlaff, N.; et al. (2011). "A catalogue of young runaway Hipparcos stars within 3 kpc from the Sun". Monthly Notices of the Royal Astronomical Society. 410 (1): 190–200. arXiv:1007.4883. Bibcode:2011MNRAS.410..190T. doi:10.1111/j.1365-2966.2010.17434.x. S2CID 118629873. Vizier catalog entry
  9. ^ Messineo, M.; Brown, A. G. A. (2019). "A Catalog of Known Galactic K-M Stars of Class I Candidate Red Supergiants in Gaia DR2". The Astronomical Journal. 158 (1): 20. arXiv:1905.03744. Bibcode:2019AJ....158...20M. doi:10.3847/1538-3881/ab1cbd. S2CID 148571616.
  10. Soubiran, Caroline; et al. (2016). "The PASTEL catalogue: 2016 version". Astronomy & Astrophysics. 591: A118. arXiv:1605.07384. Bibcode:2016A&A...591A.118S. doi:10.1051/0004-6361/201628497. S2CID 119258214.
  11. ^ 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. Vizier catalog entry
  12. De Medeiros, J. R.; Mayor, M. (1999). "A catalog of rotational and radial velocities for evolved stars". Astronomy and Astrophysics Supplement Series. 139 (3): 433. arXiv:astro-ph/0608248. Bibcode:1999A&AS..139..433D. doi:10.1051/aas:1999401. Vizier catalog entry
  13. "56 Peg". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2019-07-01.
  14. 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. Vizier catalog entry
  15. McDonald, A. R. E.; Hearnshaw, J. B. (August 1983). "The Wolf 630 moving group of stars". Monthly Notices of the Royal Astronomical Society. 204 (3): 841–852. Bibcode:1983MNRAS.204..841M. doi:10.1093/mnras/204.3.841.
  16. ^ Frankowski, A.; Jorissen, A. (February 2006). "The puzzling case of 56 Pegasi: a fast rotator seen nearly pole-on". The Observatory. 126: 25–37. arXiv:astro-ph/0512036. Bibcode:2006Obs...126...25F.
  17. van Belle, G. T.; et al. (2009). "Supergiant temperatures and linear radii from near-infrared interferometry". Monthly Notices of the Royal Astronomical Society. 394 (4): 1925. arXiv:0811.4239. Bibcode:2009MNRAS.394.1925V. doi:10.1111/j.1365-2966.2008.14146.x. S2CID 118372600.
  18. Martínez, M. Isabel Pérez; et al. (2011). "The basal chromospheric Mg ii h+k flux of evolved stars: Probing the energy dissipation of giant chromospheres". Monthly Notices of the Royal Astronomical Society. 414 (1): 418. arXiv:1102.4832. Bibcode:2011MNRAS.414..418P. doi:10.1111/j.1365-2966.2011.18421.x. S2CID 59268230. Vizier catalog entry
  19. Schindler, M.; et al. (December 1982). "Ultraviolet and X-ray detection of the 56 Pegasi system /K0 IIp + WD/ - Evidence for accretion of a cool stellar wind onto a white dwarf". Astrophysical Journal, Part 1. 263: 269–276. Bibcode:1982ApJ...263..269S. doi:10.1086/160501.
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