42 Capricorni

42 Capricorni is a binary star[10] system in the zodiac constellation of Capricornus. It has a combined apparent visual magnitude of 5.18,[2] so it is faintly visible to the naked eye. Its annual parallax shift of 30.09 mas yields a distance estimate of about 108 light years; the system is moving closer to the Sun with a radial velocity of −1.2 km/s.[5] 42 Capricorni is 0.2 degree south of the ecliptic and so is subject to lunar occultations.[11]

42 Capricorni
Observation data
Epoch J2000      Equinox
Constellation Capricornus
Right ascension 21h 41m 32.85882s[1]
Declination −14° 02′ 51.3964″[1]
Apparent magnitude (V) 5.18[2]
Characteristics
Spectral type G1 IV[3] (G1 IV + G2 V)[4]
U−B color index +0.20[2]
B−V color index +0.65[2]
Variable type RS CVn[4]
Astrometry
Radial velocity (Rv)−1.20±0.05[5] km/s
Proper motion (μ) RA: −123.05[1] mas/yr
Dec.: −308.50[1] mas/yr
Parallax (π)30.09 ± 0.32[1] mas
Distance108 ± 1 ly
(33.2 ± 0.4 pc)
Absolute magnitude (MV)+2.73[6] (2.79 + 4.73)[4]
Orbit[7]
Period (P)13.174 d
Eccentricity (e)0.1763±0.0025
Periastron epoch (T)2447863.626 ± 0.027 JD
Argument of periastron (ω)
(secondary)		166.45±0.83°
Semi-amplitude (K1)
(primary)		25.57±0.06 km/s
Semi-amplitude (K2)
(secondary)		35.16±0.25 km/s
Details
42 Cap A
Mass1.09[8] M☉
Radius2.6[4] R☉
Surface gravity (log g)3.76[3] cgs
Temperature5,634[3] K
Metallicity [Fe/H]−0.10[3] dex
Rotational velocity (v sin i)5.2[4] km/s
Age6.7[8] Gyr
42 Cap B
Rotational velocity (v sin i)4.4[4] km/s
Other designations
BY Cap, 42 Cap, BD−14° 6102, FK5 1150, HD 206301, HIP 107095, HR 8283, SAO 164580[9]
Database references
SIMBADdata

This is a double-lined close spectroscopic binary with an orbital period of 13.174 days and an eccentricity of 0.18.[7] The binary nature of this system was discovered in 1918 by the English astronomer Joseph Lunt. It has a combined spectrum that matches a stellar classification of G1 IV,[3] with the individual components having estimated classes of G1 V and G2 V. This is an RS Canum Venaticorum variable, indicating the presence of an active chromosphere with star spots.[4] The system is a source of X-ray emission.[12]

References
  1. 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. 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. Gray, R. O.; et al. (2006), "Contributions to the Nearby Stars (NStars) Project: Spectroscopy of Stars Earlier than M0 within 40 pc--The Southern Sample", The Astronomical Journal, 132 (1): 161–170, arXiv:astro-ph/0603770, Bibcode:2006AJ....132..161G, doi:10.1086/504637, S2CID 119476992.
  4. Fekel, Francis C. (December 1997), "Chromospherically active stars. XVI. The double-lined binary 42 Capricorni", Astronomical Journal, 114: 2747, Bibcode:1997AJ....114.2747F, doi:10.1086/118683
  5. Karataş, Y.; Bilir, S.; Eker, Z.; Demircan, O. (2004), "Kinematics of chromospherically active binaries and evidence of an orbital period decrease in binary evolution", Monthly Notices of the Royal Astronomical Society, 349 (3): 1069, arXiv:astro-ph/0404219, Bibcode:2004MNRAS.349.1069K, doi:10.1111/j.1365-2966.2004.07588.x, S2CID 15290475.
  6. Ammler-von Eiff, M.; Reiners, A. (June 2012), "New measurements of rotation and differential rotation in A-F stars: are there two populations of differentially rotating stars?", Astronomy & Astrophysics, 542: A116, arXiv:1204.2459, Bibcode:2012A&A...542A.116A, doi:10.1051/0004-6361/201118724, S2CID 53666672.
  7. Pourbaix, D.; et al. (2004), "SB9: The Ninth Catalogue of Spectroscopic Binary Orbits", Astronomy & Astrophysics, 424: 727–732, arXiv:astro-ph/0406573, Bibcode:2004A&A...424..727P, doi:10.1051/0004-6361:20041213, S2CID 119387088.
  8. Chen, Y. Q.; et al. (February 2000), "Chemical composition of 90 F and G disk dwarfs", Astronomy and Astrophysics Supplement, 141 (3): 491–506, arXiv:astro-ph/9912342, Bibcode:2000A&AS..141..491C, doi:10.1051/aas:2000124, S2CID 16273589.
  9. "42 Cap". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2018-01-27.
  10. Eggleton, P. P.; Tokovinin, A. A. (September 2008), "A catalogue of multiplicity among bright stellar systems", Monthly Notices of the Royal Astronomical Society, 389 (2): 869–879, arXiv:0806.2878, Bibcode:2008MNRAS.389..869E, doi:10.1111/j.1365-2966.2008.13596.x, S2CID 14878976.
  11. Herr, Richard B. (April 1969), "Identification List of Spectroscopic and Eclipsing Binaries Subject to Occultations by the Moon", Publications of the Astronomical Society of the Pacific, 81 (479): 105, Bibcode:1969PASP...81..105H, doi:10.1086/128748.
  12. Haakonsen, Christian Bernt; Rutledge, Robert E. (September 2009), "XID II: Statistical Cross-Association of ROSAT Bright Source Catalog X-ray Sources with 2MASS Point Source Catalog Near-Infrared Sources", The Astrophysical Journal Supplement, 184 (1): 138–151, arXiv:0910.3229, Bibcode:2009ApJS..184..138H, doi:10.1088/0067-0049/184/1/138, S2CID 119267456.
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