Upsilon Pegasi

Upsilon Pegasi, Latinised from υ Pegasi, is a star within the great square[10] in the northern constellation of Pegasus. It has the proper name Alkarab /ˈælkəræb/.[11] This object has a yellow-white hue and is faintly visible to the naked eye with an apparent magnitude of 4.40.[2] It is located at a distance of approximately 170 light-years from the Sun based on parallax,[1] but is drifting closer with a radial velocity of −8.6 km/s.[5] The star is moving through the Galaxy at a speed of 50.6 km/s relative to the Sun. Its projected Galactic orbit carries it between 18,600 and 26,300 light-years from the center of the Galaxy.[6]

Upsilon Pegasi
Location of υ Pegasi (circled)
Observation data
Epoch J2000      Equinox J2000
Constellation Pegasus
Right ascension  23h 25m 22.78350s[1]
Declination +23° 24′ 14.7606″[1]
Apparent magnitude (V) 4.40[2]
Characteristics
Evolutionary stage Hertzsprung gap[3]
Spectral type F8III[4]
U−B color index +0.14[2]
B−V color index +0.61[2]
Astrometry
Radial velocity (Rv)−8.59[5] km/s
Proper motion (μ) RA: +192.19[1] mas/yr
Dec.: +36.12[1] mas/yr
Parallax (π)19.14 ± 0.18[1] mas
Distance170 ± 2 ly
(52.2 ± 0.5 pc)
Absolute magnitude (MV)0.83[6]
Details
Mass2.17[7] M☉
Radius5.97+0.36
−0.19[8] R☉
Luminosity43.2±0.8[8] L☉
Surface gravity (log g)3.22[7] cgs
Temperature6,061+97
−176[8] K
Metallicity [Fe/H]−0.01[6] dex
Rotational velocity (v sin i)73.4[3] km/s
Other designations
Alkarab, υ Peg, 68 Pegasi, BD+22°4833, FK5 881, GC 32585, HD 220657, HIP 115623, HR 8905, SAO 91253[9]
Database references
SIMBADdata

This object is an aging giant star with a stellar classification of F8III.[4] It is currently in the Hertzsprung gap and is a source of X-ray emission.[3] The star has 2.2[7] times the mass of the Sun and is spinning with a projected rotational velocity of 73.4 km/s.[3] It has an iron abundance of −0.01 dex, or 97.7% of the Sun's. Upsilon Pegasi has six times the girth of the Sun and is radiating 43 times the Sun's luminosity at an effective temperature of 6,061 K.[8]

Nomenclature

υ Pegasi is the star's Bayer designation. The star bore the traditional Arabic name Al Karab ("the Bucket-rope").[12] In 2016, the IAU organized a Working Group on Star Names (WGSN)[13] to catalog and standardize proper names for stars. The WGSN approved the name Alkarab for this star on 5 September 2017 and it is now so included in the List of IAU-approved Star Names.[11]

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References
  1. Van Leeuwen, F. (2007). "Validation of the new Hipparcos reduction". Astronomy and Astrophysics. 474 (2): 653. arXiv:0708.1752. Bibcode:2007A&A...474..653V. doi:10.1051/0004-6361:20078357. Vizier catalog entry
  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. Schröder, C.; et al. (January 2009). "Ca II HK emission in rapidly rotating stars. Evidence for an onset of the solar-type dynamo". Astronomy and Astrophysics. 493 (3): 1099–1107. Bibcode:2009A&A...493.1099S. doi:10.1051/0004-6361:200810377.
  4. Gray, R. O.; Napier, M. G.; Winkler, L. I. (2001). "The Physical Basis of Luminosity Classification in the Late A-, F-, and Early G-Type Stars. I. Precise Spectral Types for 372 Stars". The Astronomical Journal. 121 (4): 2148. Bibcode:2001AJ....121.2148G. doi:10.1086/319956.
  5. Massarotti, Alessandro; Latham, David W.; Stefanik, Robert P.; Fogel, Jeffrey (2008). "Rotational and Radial Velocities for a Sample of 761 Hipparcos Giants and the Role of Binarity". The Astronomical Journal. 135: 209. Bibcode:2008AJ....135..209M. doi:10.1088/0004-6256/135/1/209.
  6. 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. Vizier catalog entry
  7. Allende Prieto, C.; Lambert, D. L. (1999). "Fundamental parameters of nearby stars from the comparison with evolutionary calculations: Masses, radii and effective temperatures". Astronomy and Astrophysics. 352: 555. arXiv:astro-ph/9911002. Bibcode:1999A&A...352..555A. Vizier catalog entry
  8. 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.
  9. "ups Peg". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2019-10-21.
  10. Harrington, Philip S. (2010). Cosmic Challenge: The Ultimate Observing List for Amateurs. Cambridge University Press. p. 50. ISBN 9781139493680.
  11. "Naming Stars". IAU.org. Retrieved 16 December 2017.
  12. Allen, Richard Hinckley (1963) [1899]. Star Names: Their Lore and Meaning (Reprint ed.). New York, NY: Dover Publications Inc. p. 329. ISBN 0-486-21079-0.
  13. "IAU Working Group on Star Names (WGSN)". Retrieved 22 May 2016.
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