57 Pegasi
Binary star in the constellation Pegasus
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
^ 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 .
^ a b c d e f 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 .
^ a b c d e f g 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 .
^ a b c 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 .
^ a b c d e f 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 .
^ a b Wilson, Ralph Elmer (1953), "General catalogue of stellar radial velocities", Washington , Carnegie Institution of Washington: 0, Bibcode :1953GCRV..C......0W .
^ 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 .
^ a b c d 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.
^ a b c 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 .
^ "57 Peg" , SIMBAD , Centre de données astronomiques de Strasbourg , retrieved 2021-05-16 .
^ 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 .
^ Bakos, G. A. (1978), "Spectrographic and Photometric Investigation of 57 Pegasi", Bulletin of the Astronomical Institute of Czechoslovakia , 29 : 252, Bibcode :1978BAICz..29..252B .
^ 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