57 Pegasi

A broadband optical light curve for GZ Pegasi, adapted from Tabur et al. (2009)[1]
Observation data
Epoch J2000.0      Equinox J2000.0
Constellation Pegasus
Right ascension 23h 09m 31.45738s[2]
Declination +08° 40′ 37.7636″[2]
Apparent magnitude (V) 5.105[3] (4.95 to 5.23)[4]
Characteristics
Evolutionary stage Asymptotic giant branch[5] + main sequence[3]
Spectral type M4IIIa + A3V[3]
U−B color index 1.272[3]
B−V color index 1.452[3]
Variable type SRa[4]
Astrometry
Radial velocity (Rv)+14.0±0.9[6] km/s
Proper motion (μ) RA: +4.28[2] mas/yr
Dec.: −6.29[2] mas/yr
Parallax (π)4.17 ± 0.34 mas[2]
Distance780 ± 60 ly
(240 ± 20 pc)
Absolute magnitude (MV)−1.83[7]
Details
Aa
Mass3 M☉[8]
2[5] M☉
Radius126+23
−17[9] R☉
Luminosity2,697±311[9] L☉
Surface gravity (log g)0.06[5] cgs
Temperature3,707+387
−227[9] K
Metallicity [Fe/H]−0.99[5] dex
Ab
Mass1.9[8] M☉
Other designations
57 Peg, GZ Peg, BD+07°4981, HD 218634, HIP 114347, HR 8815, SAO 128001, WDS 23095+0841[10]
Database references
SIMBADdata

57 Pegasi is a variable binary star system in the northern constellation of Pegasus (constellation). It has the variable star designation GZ Pegasi, while 57 Pegasi is the Flamsteed designation. The system is faintly visible to the naked eye as a point of light with an apparent visual magnitude that fluctuates around 5.105.[3] It is located at a distance of approximately 780 light years from the Sun based on parallax,[2] and is drifting further away with a radial velocity of +14 km/s.[6]

The variability of this star was discovered by J. Stebbins and C. M. Huffer in 1930.[11] It was classified as a long-period variable of type Lb in 1974. However, based on a constant period and the shape of the light curve, it was later reclassified as a semiregular variable of type SRa in 1978.[12] It varies in brightness from magnitude 4.95 down to 5.23 with a period of 92.66 days.[4] The spectrum of 57 Peg displays blended features that indicate this is a binary system consisting of an aging red giant star on the asymptotic giant branch[5] with a stellar classification of M4IIIa, and a fainter but hotter A-type main-sequence companion of class A3V.[3] This spectroscopic binary system has poorly constrained orbital elements with an estimated orbital period of 100–500 years.[8]

The red giant primary has been designated as an S-type star that shows enriched levels of s-process elements in its spectrum. However, it does not display significant lines of radioactive technetium-99 in its spectrum, indicating that the s-process elements must have been acquired from a mass transfer event from a formerly asymptotic giant branch companion that had passed through multiple dredge-up events.[5] This would suggest it has a white dwarf as a tertiary companion, but this is incompatible with the data findings. Instead, it might have been misclassified as an S-type star.[8]

There is a magnitude 10.06 visual companion at an angular separation of 32.6″ along a position angle of 198° from the primary, as of 2015. Designated component B, this star was first reported by F. G. W. Struve in 1827.[13]

References

  1. ↑ Tabur, V.; Bedding, T. R.; Kiss, L. L.; Moon, T. T.; Szeidl, B.; Kjeldsen, H. (December 2009). "Long-term photometry and periods for 261 nearby pulsating M giants". Monthly Notices of the Royal Astronomical Society. 400 (4): 1945–1961. arXiv:0908.3228. Bibcode:2009MNRAS.400.1945T. doi:10.1111/j.1365-2966.2009.15588.x. S2CID 15358380. Retrieved 12 February 2022.
  2. 1 2 3 4 5 6 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.
  3. 1 2 3 4 5 6 7 Hackos, W. Jr.; Peery, B. F. Jr. (August 1968), "Spectroscopic binary 57 Pegasi", Astronomical Journal, 73: 504–507, Bibcode:1968AJ.....73..504H, doi:10.1086/110651.
  4. 1 2 3 Samus, N. N.; et al. (2017), "General Catalogue of Variable Stars", Astronomy Reports, 5.1, 61 (1): 80–88, Bibcode:2017ARep...61...80S, doi:10.1134/S1063772917010085, S2CID 125853869.
  5. 1 2 3 4 5 6 Pompéia, L. (September 2009), "Chemical Abundances of the S Star GZ Peg", Publications of the Astronomical Society of Australia, 26 (3): 354–358, arXiv:0903.1053, Bibcode:2009PASA...26..354P, doi:10.1071/AS08041, S2CID 15407375.
  6. 1 2 Wilson, Ralph Elmer (1953), "General catalogue of stellar radial velocities", Washington, Carnegie Institution of Washington: 0, Bibcode:1953GCRV..C......0W.
  7. ↑ 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.
  8. 1 2 3 4 Jorissen, A.; et al. (June 2019), "Barium and related stars, and their white-dwarf companions. I. Giant stars", Astronomy & Astrophysics, 626: 28, arXiv:1904.03975, Bibcode:2019A&A...626A.127J, doi:10.1051/0004-6361/201834630, S2CID 102351666, A127.
  9. 1 2 3 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.
  10. ↑ "57 Peg", SIMBAD, Centre de données astronomiques de Strasbourg, retrieved 2021-05-16.
  11. ↑ Tremko, J.; Bakos, G. A. (November 1986), "The semiregular variable 57 Pegasi", Journal of the Royal Astronomical Society of Canada, 80: 230–239, Bibcode:1986JRASC..80..230T.
  12. ↑ Bakos, G. A. (1978), "Spectrographic and Photometric Investigation of 57 Pegasi", Bulletin of the Astronomical Institute of Czechoslovakia, 29: 252, Bibcode:1978BAICz..29..252B.
  13. ↑ Mason, B. D.; et al. (2014), "The Washington Visual Double Star Catalog", The Astronomical Journal, 122 (6): 3466, Bibcode:2001AJ....122.3466M, doi:10.1086/323920, retrieved 2015-07-22
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