Astronomy:Gamma Pegasi

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Short description: Variable B-type star in the constellation Pegasus
Gamma Pegasi
Pegasus constellation map.svg
Red circle.svg
Location of γ Pegasi (circled)
Observation data
Equinox J2000.0]] (ICRS)
Constellation Pegasus
Right ascension  00h 13m 14.15123s[1]
Declination +15° 11′ 00.9368″[1]
Apparent magnitude (V) +2.78 - 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[1] mas/yr
Dec.: –9.28[1] mas/yr
Parallax (π)6.9474 ± 0.4293[7] mas
Distance470 ± 30 ly
(144 ± 9 pc)
Absolute magnitude (MV)−2.64[8]
Details
Mass8.9±0.1[3] M☉
Radius4.80±0.39[9] R☉
Luminosity5,840[10] L☉
Surface gravity (log g)3.98±0.06[9] cgs
Temperature21179±237[9] K
Metallicity [Fe/H]−0.34[11] dex
Rotational velocity (v sin i)0[12] km/s
Age18.7±3.2[3] Myr
Other designations
Algenib, gam Peg, 88 Peg, FK5 7, HD 886, HIP 1067, HR 39, SAO 91781[13]
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/;[14][15] 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

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)[16] to catalog and standardize proper names for stars. The WGSN's first bulletin of July 2016[17] 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 .[18] Consequently, the Chinese name for γ Pegasi itself is 壁宿一 (Bìxiù yī, English: the First Star of Wall.)[19]

Properties

A light curve for Gamma Pegasi, plotted from TESS data[20]

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.)[21] 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] Its magnitude varies between +2.78 and +2.89 over the course of each pulsation cycle.

This is a large star with almost nine[3] times the mass of the Sun and close to five[9] times the Sun's radius. 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. It is either rotating very slowly with no measurable rotational velocity or else it is being viewed from nearly pole-on.[12] Gamma Pegasi has a total luminosity of 5,840 times that of the Sun,[10] which is being radiated from its outer atmosphere at an effective temperature of more than 21,000 K.[9] At this temperature, the star glows with a blue-white hue.[22]

The star has a weak magnetic field (from -10 G to 30 G,[23] an upper bound on a dipolar magnetic field strength of about 40 G[24]).

References

  1. ↑ 1.0 1.1 1.2 1.3 van Leeuwen, F. (November 2007), "Validation of the new Hipparcos reduction", Astronomy and Astrophysics 474 (2): 653–664, doi:10.1051/0004-6361:20078357, Bibcode: 2007A&A...474..653V 
  2. ↑ Samus, N. N. et al. (2017). "General Catalogue of Variable Stars". Astronomy Reports. 5.1 61 (1): 80–88. doi:10.1134/S1063772917010085. Bibcode: 2017ARep...61...80S. 
  3. ↑ 3.0 3.1 3.2 3.3 3.4 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, doi:10.1111/j.1365-2966.2010.17434.x, Bibcode: 2011MNRAS.410..190T 
  4. ↑ 4.0 4.1 4.2 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, doi:10.1086/111220, Bibcode: 1971AJ.....76.1058C 
  5. ↑ 5.0 5.1 5.2 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, doi:10.1002/asna.201011456, Bibcode: 2010AN....331.1057W 
  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. (2021). "Gaia Early Data Release 3: Summary of the contents and survey properties". Astronomy & Astrophysics 649: A1. doi:10.1051/0004-6361/202039657. Bibcode: 2021A&A...649A...1G.  Gaia EDR3 record for this source at VizieR.
  8. ↑ Huang, W. et al. (2012), "A catalogue of Paschen-line profiles in standard stars", Astronomy & Astrophysics 547: A62, doi:10.1051/0004-6361/201219804, Bibcode: 2012A&A...547A..62H. 
  9. ↑ 9.0 9.1 9.2 9.3 9.4 Fitzpatrick, E. L.; Massa, D. (March 2005), "Determining the Physical Properties of the B Stars. II. Calibration of Synthetic Photometry", The Astronomical Journal 129 (3): 1642–1662, doi:10.1086/427855, Bibcode: 2005AJ....129.1642F 
  10. ↑ 10.0 10.1 Hohle, M. M.; Neuhäuser, R.; Schutz, B. F. (April 2010), "Masses and luminosities of O- and B-type stars and red supergiants", Astronomische Nachrichten 331 (4): 349, doi:10.1002/asna.200911355, Bibcode: 2010AN....331..349H 
  11. ↑ 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, doi:10.1086/171116, Bibcode: 1992ApJ...387..673G 
  12. ↑ 12.0 12.1 Abt, Helmut A.; Levato, Hugo; Grosso, Monica (July 2002), "Rotational Velocities of B Stars", The Astrophysical Journal 573 (1): 359–365, doi:10.1086/340590, Bibcode: 2002ApJ...573..359A . The zero value is for v sin i, so v and/or i must be small.
  13. ↑ "gam Peg". SIMBAD. Centre de données astronomiques de Strasbourg. http://simbad.u-strasbg.fr/simbad/sim-basic?Ident=gam+Peg. 
  14. ↑ 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. 
  15. ↑ "IAU Catalog of Star Names". http://www.pas.rochester.edu/~emamajek/WGSN/IAU-CSN.txt. 
  16. ↑ "IAU Working Group on Star Names (WGSN)". https://www.iau.org/science/scientific_bodies/working_groups/280/. 
  17. ↑ "Bulletin of the IAU Working Group on Star Names, No. 1". http://www.pas.rochester.edu/~emamajek/WGSN/WGSN_bulletin1.pdf. 
  18. ↑ (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.
  19. ↑ (in Chinese) 香港太空館 – 研究資源 – 亮星中英對照表 , Hong Kong Space Museum. Accessed on line November 23, 2010.
  20. ↑ "MAST: Barbara A. Mikulski Archive for Space Telescopes". Space Telescope Science Institute. https://mast.stsci.edu/portal/Mashup/Clients/Mast/Portal.html. 
  21. ↑ 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, doi:10.1086/126561, Bibcode: 1953PASP...65..144M 
  22. ↑ "The Colour of Stars", Australia Telescope, Outreach and Education (Commonwealth Scientific and Industrial Research Organisation), December 21, 2004, http://outreach.atnf.csiro.au/education/senior/astrophysics/photometry_colour.html, retrieved 2012-01-16 
  23. ↑ 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.". 
  24. ↑ Neiner, C. et al. (February 2014), "γ Pegasi: testing Vega-like magnetic fields in B stars", Astronomy & Astrophysics 562: 8, doi:10.1051/0004-6361/201323093, A59, Bibcode: 2014A&A...562A..59N, https://hal-cea.archives-ouvertes.fr/cea-01162433, "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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