18 Monocerotis

18 Monocerotis is a binary star system located about half way from Orion's Belt to Procyon,[6] in the equatorial constellation of Monoceros.[11] It is visible to the naked eye as a faint, orange-hued star with an apparent visual magnitude of 4.47,[2] and is positioned around 370[1] light years away from the Sun based on parallax. The system is receding from the Earth with a heliocentric radial velocity of +11 km/s.[4]

18 Monocerotis
Location of 18 Monocerotis (circled red)
Observation data
Epoch J2000      Equinox J2000
Constellation Monoceros
Right ascension  06h 47m 51.64752s[1]
Declination 2° 24′ 43.7737″[1]
Apparent magnitude (V) 4.47[2]
Characteristics
Spectral type K0+IIIaBa0.2[3]
U−B color index +1.04[2]
B−V color index +1.11[2]
Astrometry
Radial velocity (Rv)+11.29[4] km/s
Proper motion (μ) RA: -16.898[1] mas/yr
Dec.: -16.229[1] mas/yr
Parallax (π)8.0947 ± 0.2385[1] mas
Distance400 ± 10 ly
(124 ± 4 pc)
Absolute magnitude (MV)-0.78[5]
Orbit[6][7]
Primary18 Monocerotis A
Companion18 Monocerotis B
Period (P)1760.9±1.9 d
Semi-major axis (a)6.63 mas
Eccentricity (e)0.40±0.04
Inclination (i)96.25°
Longitude of the node (Ω)47.63°
Periastron epoch (T)2441942.5
Argument of periastron (ω)
(secondary)		172±6°
Details
18 Mon A
Radius26.95+1.56
−0.81[1] R☉
Luminosity311.2±10.5[1] L☉
Surface gravity (log g)2.59[8] cgs
Temperature4,750[9] K
Metallicity [Fe/H]-0.03[5] dex
Rotational velocity (v sin i)< 2.0[10] km/s
Other designations
18 Mon, BD+02°1397, FK5 258, GC 8892, HD 49293, HIP 32578, HR 2506, SAO 114428[11]
Database references
SIMBADdata

It is reported as a single-lined spectroscopic binary with an orbital period of 1,760.9 days (4.8 years) and an eccentricity of 0.4.[6] The visible component is an aging K-type giant star with a stellar classification of K0+IIIaBa0.2,[3] showing a slight overabundance of barium. The spectrum displays strong violet lines of CN.[6] With the supply of hydrogen at its core exhausted, this star has expanded to 27[1] times the radius of the Sun. It is radiating 311[1] times the luminosity of the Sun from its swollen photosphere at an effective temperature of 4,750 K.[9]

References
  1. 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.
  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. Hoffleit, D.; Warren, W. H. (1995). "VizieR Online Data Catalog: Bright Star Catalogue, 5th Revised Ed. (Hoffleit+, 1991)". VizieR On-line Data Catalog: V/50. Originally Published in: 1964BS....C......0H. 5050. Bibcode:1995yCat.5050....0H.
  4. Famaey, B.; Jorissen, A.; Luri, X.; Mayor, M.; Udry, S.; Dejonghe, H.; Turon, C. (2005). "Local kinematics of K and M giants from CORAVEL/Hipparcos/Tycho-2 data". Astronomy & Astrophysics. 430: 165. arXiv:astro-ph/0409579. Bibcode:2005A&A...430..165F. doi:10.1051/0004-6361:20041272.
  5. 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
  6. Griffin, R. F. (1984). "Spectroscopic binary orbits from photoelectric radial velocities. Paper 59: 18 Monocerotis". The Observatory. 104: 267. Bibcode:1984Obs...104..267G.
  7. ESA (1997). "The Hipparcos and Tycho Catalogues". VizieR On-line Data Catalog. Bibcode:1997yCat.1239....0E.
  8. Soubiran, Caroline; Le Campion, Jean-François; Brouillet, Nathalie; Chemin, Laurent (2016). "The PASTEL catalogue: 2016 version". Astronomy & Astrophysics. 591: A118. arXiv:1605.07384. Bibcode:2016A&A...591A.118S. doi:10.1051/0004-6361/201628497.
  9. Gontcharov, G. A. (2009). "Red giant clump in the Tycho-2 catalogue". Astronomy Letters. 34 (11): 785. arXiv:1607.00619. Bibcode:2008AstL...34..785G. doi:10.1134/S1063773708110078. Vizier catalog entry
  10. De Medeiros, J. R.; Mayor, M. (1999). "A catalog of rotational and radial velocities for evolved stars". Astronomy and Astrophysics Supplement Series. 139 (3): 433. arXiv:astro-ph/0608248. Bibcode:1999A&AS..139..433D. doi:10.1051/aas:1999401. Vizier catalog entry
  11. "18 Mon". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2019-05-30.
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