45 Cancri

45 Cancri is a binary star[4] system in the zodiac constellation of Cancer, located 680 light years away from the Sun.[1] It has the Bayer designation A1 Cancri;[7] 45 Cancri is the Flamsteed designation. It is visible to the naked eye as a faint, white-hued star at an apparent visual magnitude of 5.62.[2] The pair form a double-lined spectroscopic binary with an orbital period of 2.76 years and an eccentricity of 0.46.[4] They are drifting closer to the Earth with a heliocentric radial velocity of −6 km/s.[2]

This article is about A1 Cancri. For other stars with this Bayer designation, see A Cancri.
45 Cancri
Observation data
Epoch J2000.0      Equinox J2000.0
Constellation Cancer
Right ascension  08h 43m 12.32940s[1]
Declination +12° 40′ 51.1486″[1]
Apparent magnitude (V) 5.62[2]
Characteristics
Spectral type G8 III and A3 III[3]
B−V color index 0.435±0.005[2]
Astrometry
Radial velocity (Rv)−6.2±2.3[2] km/s
Proper motion (μ) RA: −9.828[1] mas/yr
Dec.: +0.916[1] mas/yr
Parallax (π)4.7700 ± 0.1025[1] mas
Distance680 ± 10 ly
(210 ± 5 pc)
Absolute magnitude (MV)−1.62[2]
Orbit[4]
Period (P)1009.36±0.12 d
Eccentricity (e)0.461±0.002
Semi-amplitude (K1)
(primary)		20.04±0.06 km/s
Semi-amplitude (K2)
(secondary)		20.75±0.02 km/s
Details
45 Cnc A
Mass3.11±0.10[3] M☉
Radius13.86+5.03
−1.73[1] R☉
Luminosity210.3±5.4[1] L☉
Surface gravity (log g)2.72[5] cgs
Temperature5,058[5] K
Metallicity [Fe/H]−0.69±0.22[5] dex
Rotational velocity (v sin i)5.3[6] km/s
45 Cnc B
Mass3.00±0.10[3] M☉
Luminosity190.5+43.9
−35.6[3] L☉
Other designations
A1 Cnc,[7], 45 Cnc, BD+13°1972, FK5 2686, HD 74228, HIP 42795, HR 3450, SAO 98069[8]
Database references
SIMBADdata

The primary, designated component A, is an aging giant star with a stellar classification of G8 III,[9] but has most likely not yet made multiple ascents up the red giant branch.[3] It has 3.11[3] times the mass of the Sun and has expanded to 14[1] times the Sun's radius. The star is radiating 210[1] times the luminosity of the Sun from its enlarged photosphere at an effective temperature of 5,058.[5] The less evolved secondary, component B is likewise a giant star, having a class of A3 III. It has three times the mass of the Sun and shines with 191 times the Sun's luminosity.[3]

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. 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.
  3. Griffin, R. E. M.; Griffin, R. F. (February 2015), "Composite spectra: XX. 45 Cancri. Two stars with very similar masses but quite different evolutionary states", Astronomische Nachrichten, 336 (2): 178–188, Bibcode:2015AN....336..178G, doi:10.1002/asna.201412148
  4. Eggleton, Peter P.; Yakut, Kadri (July 2017), "Models for 60 double-lined binaries containing giants", Monthly Notices of the Royal Astronomical Society, 468 (3): 3533–3556, arXiv:1611.05041, Bibcode:2017MNRAS.468.3533E, doi:10.1093/mnras/stx598.
  5. Soubiran, Caroline; et al. (2016), "The PASTEL catalogue: 2016 version", Astronomy & Astrophysics, 591: A118, arXiv:1605.07384, Bibcode:2016A&A...591A.118S, doi:10.1051/0004-6361/201628497.
  6. Schröder, C.; et al. (January 2009), "Ca II HK emission in rapidly rotating stars. Evidence for an onset of the solar-type dynamo" (PDF), Astronomy and Astrophysics, 493 (3): 1099–1107, Bibcode:2009A&A...493.1099S, doi:10.1051/0004-6361:200810377
  7. HD 74228, HD-DM-GC-HR-HIP-Bayer-Flamsteed Cross Index, N. D. Kostjuk, Institute of Astronomy of Russian Academy of Sciences, 2002; CDS ID IV/27A.
  8. "45 Cnc". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2019-03-04.
  9. Ginestet, N.; Carquillat, J. M. (2002), "Spectral Classification of the Hot Components of a Large Sample of Stars with Composite Spectra, and Implication for the Absolute Magnitudes of the Cool Supergiant Components", The Astrophysical Journal Supplement Series, 143 (2): 513, Bibcode:2002ApJS..143..513G, doi:10.1086/342942
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