Alpha Monocerotis

Alpha Monocerotis, Latinized from α Monocerotis, is the Bayer designation for the brightest star in the equatorial constellation of Monoceros. It can be viewed with the naked eye, having an apparent visual magnitude of 3.94.[2] Based upon an annual parallax shift of 22.07 mas as seen from Earth,[1] it is located 148 light years away from the Sun. The star is moving away from the Sun with a radial velocity of +10.5 km/s.[2]

α Monocerotis
Location of α Monocerotis (circled)
Observation data
Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation Monoceros
Right ascension  07h 41m 14.833s[1]
Declination −09° 33′ 04.07″[1]
Apparent magnitude (V) 3.94[2]
Characteristics
Spectral type G9.5 III-IIIb Fe-0.5[3]
B−V color index 1.022[2]
Astrometry
Radial velocity (Rv)+10.50[2] km/s
Proper motion (μ) RA: −74.61±0.14[1] mas/yr
Dec.: −19.59±0.10[1] mas/yr
Parallax (π)22.07 ± 0.18[1] mas
Distance148 ± 1 ly
(45.3 ± 0.4 pc)
Absolute magnitude (MV)0.71±0.08[4]
Details
Mass2.02±0.29[4] M☉
Radius10.1±0.5[4] R☉
Surface gravity (log g)2.71±0.09[4] cgs
Temperature4,879[4] K
Metallicity [Fe/H]−0.01[4] dex
Rotation326 days[5]
Rotational velocity (v sin i)1.9[5] km/s
Age1.18±0.42[4] Gyr
Other designations
α Mon, 26 Monocerotis, BD−09° 2172, HD 61935, HIP 37447, HR 2970, SAO 134986[6]
Database references
SIMBADdata

The stellar classification of G9.5 III-IIIb Fe-0.5[3] indicates this is an evolved giant star of type G, which means the hydrogen has been depleted at its core and the outer envelope has expanded and cooled. The 'Fe−0.5' notation indicates the spectrum displays a slight underabundance of iron relative to other stars of this temperature. It is a red clump giant, which means it is generating energy through helium fusion at its core.[7] At the age of 1.18 billion years, this yellow-hued star has an estimated two times the mass of the Sun and 10 times the Sun's radius.[4] It is spinning sedately with a rotation period of about 326 days.[5]

References
  1. 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. Vizier catalog entry
  2. Hekker, S.; et al. (August 2006), "Precise radial velocities of giant stars. I. Stable stars", Astronomy and Astrophysics, 454 (3): 943–949, arXiv:astro-ph/0604502, Bibcode:2006A&A...454..943H, doi:10.1051/0004-6361:20064946.
  3. Keenan, Philip C; McNeil, Raymond C (1989), "The Perkins catalog of revised MK types for the cooler stars", Astrophysical Journal Supplement Series, 71: 245, Bibcode:1989ApJS...71..245K, doi:10.1086/191373.
  4. da Silva, L.; et al. (November 2006), "Basic physical parameters of a selected sample of evolved stars", Astronomy and Astrophysics, 458 (2): 609–623, arXiv:astro-ph/0608160, Bibcode:2006A&A...458..609D, doi:10.1051/0004-6361:20065105.
  5. Setiawan, J.; et al. (July 2004), "Precise radial velocity measurements of G and K giants. Multiple systems and variability trend along the Red Giant Branch", Astronomy and Astrophysics, 421: 241–254, Bibcode:2004A&A...421..241S, doi:10.1051/0004-6361:20041042-1.
  6. "alf Mon". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2017-11-08.
  7. Laney, C. D.; Joner, M. D.; Pietrzyński, G. (2012), "A new Large Magellanic Cloud K-band distance from precision measurements of nearby red clump stars", Monthly Notices of the Royal Astronomical Society, 419 (2): 1637, arXiv:1109.4800, Bibcode:2012MNRAS.419.1637L, doi:10.1111/j.1365-2966.2011.19826.x.
  • Kaler, James B. (March 23, 2007), "Alpha Monocerotis", STARS, University of Illinois, retrieved 2017-11-08.
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