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Gamma Pegasi

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"Algenib" redirects here. For the another star named Algenib, see Alpha Persei.
Gamma Pegasi
Location of γ Pegasi (circled)
Observation data
Epoch J2000      Equinox J2000
Constellation Pegasus
Right ascension 00h 13m 14.15123s[1]
Declination +15° 11′ 00.9368″[1]
Apparent magnitude (V) +2.78 to 2.89[2]
Characteristics
Spectral type B2 IV[3]
U−B color index −0.85[4]
B−V color index −0.23[4]
Variable type β Cep[5]
Astrometry
Radial velocity (Rv)+4.1[6] km/s
Proper motion (μ) RA: +1.98 mas/yr[1]
Dec.: –9.28 mas/yr[1]
Parallax (π)6.9474±0.4293 mas[7]
Distance470 ± 30 ly
(144 ± 9 pc)
Absolute magnitude (MV)−2.51±0.15[8]
Details[8]
Mass8.8±0.3 M☉
Radius5.4±0.4 R☉
Luminosity6,000+900
−800 L☉
Surface gravity (log g)3.95±0.05 cgs
Temperature22,000±400 K
Metallicity [Fe/H]−0.34[9] dex
Rotational velocity (v sin i)8[10] km/s
Age21.9+1.0
−1.4 Myr
Other designations
Algenib, γ Pegasi, 88 Pegasi, FK5 7, HD 886, HIP 1067, HR 39, SAO 91781[11]
Database references
SIMBADdata

Gamma Pegasi is a star in the constellation of Pegasus, located at the southeast corner of the asterism known as the Great Square. It has the formal name Algenib /ælˈdʒiːnɪb/;[12][13] the Bayer designation Gamma Pegasi is Latinized from γ Pegasi and abbreviated Gamma Peg or γ Peg. The average apparent visual magnitude of +2.84[4] makes this the fourth-brightest star in the constellation. The distance to this star has been measured using the parallax technique, yielding a value of roughly 470 light-years (144 parsecs).

Nomenclature

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Gamma Pegasi is the star's Bayer designation. Although it also had the traditional name Algenib, this name was also used for Alpha Persei. In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN)[14] to catalog and standardize proper names for stars. The WGSN's first bulletin of July 2016[15] included a table of the first two batches of names approved by the WGSN; which included Algenib for this star (Alpha Persei was given the name Mirfak).

The asterism of γ Pegasi and α Andromedae, in Hindu astronomy, is called Uttara Bhādrapadā (उत्तरभाद्रपदा) or Uttṛṭṭāti. It is the 26th nakshatra. In Chinese, 壁宿 (Bìxiù), meaning Wall (asterism) refers to an asterism consisting of γ Pegasi and α Andromedae .[16] Consequently, the Chinese name for γ Pegasi itself is 壁宿一 (Bìxiù yī, English: the First Star of Wall.)[17]

Properties

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A light curve for Gamma Pegasi, plotted from TESS data[18]

In 1911, American astronomer Keivin Burns discovered that the radial velocity of Gamma Pegasi varied slightly. This was confirmed in 1953 by American astronomer D. Harold McNamara, who identified it as a Beta Cephei variable.[5] (At the time he actually identified it as a Beta Canis Majoris star, which was subsequently designated a Beta Cephei variable.)[19] It has a radial pulsation period of 0.15175 days (3.642 hours), but also shows the behavior of a slowly pulsating B star (SPB) with three additional pulsational frequencies.[5] Hence it is considered a hybrid pulsator.[20] Its magnitude varies between +2.78 and +2.89 over the course of each pulsation cycle.[2]

This is a large star with 8.8 times the mass of the Sun and 5.5 times the Sun's radius.[8] The stellar classification of B2 IV[3] suggests this is a subgiant star that is exhausting the hydrogen at its core and is in the process of evolving away from the main sequence. With a projected rotational velocity of 8 km/s, it is either rotating very slowly or it is being viewed from nearly pole-on.[10] Gamma Pegasi has a total luminosity of 6,000 times that of the Sun, which is being radiated from its outer atmosphere at an effective temperature of more than 22,000 K.[8] At this temperature, the star glows with a blue-white hue.[21]

The star has a weak magnetic field (from -10 G to 30 G,[22] an upper bound on a dipolar magnetic field strength of about 40 G[23]).

References

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  1. ^ a b c van Leeuwen, F. (November 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.
  2. ^ a b 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.
  3. ^ a b Tetzlaff, N.; Neuhäuser, R.; Hohle, M. M. (January 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.
  4. ^ a b c Crawford, D. L.; Barnes, J. V.; Golson, J. C. (1971). "Four-color, H-beta, and UBV photometry for bright B-type stars in the northern hemisphere". The Astronomical Journal. 76: 1058. Bibcode:1971AJ.....76.1058C. doi:10.1086/111220.
  5. ^ a b c Walczak, P.; Daszyńska-Daszkiewicz, J. (December 2010). "Complex asteroseismology of the hybrid B-type pulsator γ Pegasi: A test of stellar opacities". Astronomische Nachrichten. 331 (9/10): 1057–1060. arXiv:1004.2366. Bibcode:2010AN....331.1057W. doi:10.1002/asna.201011456. S2CID 119218384.
  6. ^ Wilson, Ralph Elmer (1953). "General Catalogue of Stellar Radial Velocities". Carnegie Institute Washington D.C. Publication. Washington: Carnegie Institution of Washington. Bibcode:1953GCRV..C......0W.
  7. ^ Brown, A. G. A.; et al. (Gaia collaboration) (2021). "Gaia Early Data Release 3: Summary of the contents and survey properties". Astronomy & Astrophysics. 649: A1. arXiv:2012.01533. Bibcode:2021A&A...649A...1G. doi:10.1051/0004-6361/202039657. S2CID 227254300. (Erratum: doi:10.1051/0004-6361/202039657e). Gaia EDR3 record for this source at VizieR.
  8. ^ a b c d Nieva, María-Fernanda; Przybilla, Norbert (2014). "Fundamental properties of nearby single early B-type stars". Astronomy & Astrophysics. 566: A7. arXiv:1412.1418. Bibcode:2014A&A...566A...7N. doi:10.1051/0004-6361/201423373. S2CID 119227033.
  9. ^ Gies, Douglas R.; Lambert, David L. (March 10, 1992). "Carbon, nitrogen, and oxygen abundances in early B-type stars". Astrophysical Journal, Part 1. 387: 673–700. Bibcode:1992ApJ...387..673G. doi:10.1086/171116.
  10. ^ a b Negueruela, I.; Simón-Díaz, S.; De Burgos, A.; Casasbuenas, A.; Beck, P. G. (2024). "The IACOB project: XII. New grid of northern standards for the spectral classification of B-type stars". Astronomy and Astrophysics. 690. arXiv:2407.04163. Bibcode:2024A&A...690A.176N. doi:10.1051/0004-6361/202449298.
  11. ^ "gam Peg". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2012-02-23.
  12. ^ Kunitzsch, Paul; Smart, Tim (2006). A Dictionary of Modern star Names: A Short Guide to 254 Star Names and Their Derivations (2nd rev. ed.). Cambridge, Massachusetts: Sky Pub. ISBN 978-1-931559-44-7.
  13. ^ "IAU Catalog of Star Names". Retrieved 28 July 2016.
  14. ^ "IAU Working Group on Star Names (WGSN)". Retrieved 22 May 2016.
  15. ^ "Bulletin of the IAU Working Group on Star Names, No. 1" (PDF). Retrieved 28 July 2016.
  16. ^ (in Chinese) p. 170, 中國星座神話, written by 陳久金. Published by 台灣書房出版有限公司, 2005, ISBN 978-986-7332-25-7.
  17. ^ (in Chinese) 香港太空館 – 研究資源 – 亮星中英對照表 Archived October 25, 2008, at the Wayback Machine, Hong Kong Space Museum. Accessed on line November 23, 2010.
  18. ^ "MAST: Barbara A. Mikulski Archive for Space Telescopes". Space Telescope Science Institute. Retrieved 8 December 2021.
  19. ^ McNamara, D. H. (June 1953). "Gamma Pegasi: A Beta Canis Majoris Star of Small Velocity Amplitude". Publications of the Astronomical Society of the Pacific. 65 (384): 144. Bibcode:1953PASP...65..144M. doi:10.1086/126561.
  20. ^ Handler, G.; et al. (June 2009). "Asteroseismology of Hybrid Pulsators Made Possible: Simultaneous MOST Space Photometry and Ground-Based Spectroscopy of γ Peg". The Astrophysical Journal Letters. 698 (1): L56 – L59. arXiv:0905.1193. Bibcode:2009ApJ...698L..56H. doi:10.1088/0004-637X/698/1/L56.
  21. ^ "The Colour of Stars". Australia Telescope, Outreach and Education. Commonwealth Scientific and Industrial Research Organisation. December 21, 2004. Archived from the original on 2012-03-18. Retrieved 2012-01-16.
  22. ^ Butkovskaya V.V., Plachinda S.I. (2007). "A study of the β Cephei star γ Pegasi: binarity, magnetic field, rotation, and pulsations". Astronomy and Astrophysics. 469 (3 Jul): 1069–1076. doi:10.1051/0004-6361:20065563. We have detected the presence of a weak magnetic field on the star. The longitudinal component of the field varies from -10 G to 30 G with the stellar rotation. The most probable rotational period is P_rot = 6.6538 ± 0.0016 days. Both the orbital and the rotational periods are integral multiples of the difference between them: P_orb/|P_orb - P_rot| = 42.002, and P_rot/|P_orb - P_rot| = 41.002. Variation in the longitudinal magnetic field during the pulsation period with an amplitude about 7 G was detected.
  23. ^ Neiner, C.; et al. (February 2014). "γ Pegasi: testing Vega-like magnetic fields in B stars". Astronomy & Astrophysics. 562: 8. arXiv:1312.3521. Bibcode:2014A&A...562A..59N. doi:10.1051/0004-6361/201323093. S2CID 54652836. A59. We find that no magnetic signatures are visible in the very high quality spectropolarimetric data. The average longitudinal field measured in the Narval data is Bl = −0.1 ± 0.4 G. We derive a very strict upper limit of the dipolar field strength of Bpol ~ 40 G.
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