40 Cancri

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40 Cancri
Observation data
Epoch J2000.0      Equinox J2000.0
Constellation Cancer
Right ascension  08h 40m 11.45280s[1]
Declination +19° 58′ 16.0852″[1]
Apparent magnitude (V) 6.61[2]
Evolutionary stage main sequence
Spectral type A1 V[3]
B−V color index 0.006±0.005[2]
Radial velocity (Rv)+34.4±0.6[2] km/s
Proper motion (μ) RA: −35.312[1] mas/yr
Dec.: −13.595[1] mas/yr
Parallax (π)5.2065 ± 0.0713[1] mas
Distance626 ± 9 ly
(192 ± 3 pc)
Absolute magnitude (MV)0.32[2]
Mass2.46±0.12[4] M
Radius2.72±0.12[4] R
Luminosity73.68[2] L
Surface gravity (log g)3.78[5] cgs
Temperature9,382[5] K
Rotational velocity (v sin i)10[5] km/s
Other designations
40 Cnc, BD+20°2159, HD 73666, HIP 42523, SAO 80336, WDS J08401+2000[6]
Database references

40 Cancri is a binary star[4] system in the zodiac constellation of Cancer, located about 614[1] light years from the Sun in the Beehive Cluster (NGC 2632).[4] It is a challenge to view with the naked eye, having an apparent visual magnitude of 6.61.[2] The system is moving further from the Earth with a heliocentric radial velocity of 34 km/s.[2]

The primary component appears to be a normal A-type main-sequence star with a stellar classification of A1 V,[3] showing neither an organized magnetic field nor a chemical peculiarity.[5] However, it has an excessive temperature for its luminosity, and thus is considered an extreme[4] blue straggler;[7] this is a second generation star formed through a collision of two low mass stars some 5–350 million years ago. The collision was either between two separate cluster members or the coalescence of a binary star system.[4]

With an effective temperature of 9,382[5] K, this is the hottest star in the cluster[7] by about 1,200 K, it has 2.46 times the mass of the Sun and 2.72 times the Sun's radius. The star has an unusually slow rotation for an A1V star,[4] with a projected rotational velocity of 10 km/s,[5] it is radiating 74[2] times the Sun's luminosity from its photosphere.

40 Cancri has a common proper motion companion, located at an angular separation of 0.425±0.009 along a position angle of 127.6°±0.5°, as of 1983. This object is about 2.5±0.5 magnitudes dimmer than the primary, and is most likely an F-type star with a mass of about 1.5 M. The projected separation between the pair is 80 AU, so their orbital period is 450 years or greater.[4]


  1. ^ a b c d e f 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. ^ a b c d e f g h 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. ^ a b Bidelman, William P. (August 1956), "Spectral Classification of the Brighter Stars of the Praesepe Cluster", Publications of the Astronomical Society of the Pacific, 68 (403): 318, Bibcode:1956PASP...68..318B, doi:10.1086/126944.
  4. ^ a b c d e f g h Fossati, L.; et al. (January 2010), "Explaining the Praesepe blue straggler HD 73666", Astronomy and Astrophysics, 510, arXiv:0911.1874, Bibcode:2010A&A...510A...8F, doi:10.1051/0004-6361/200811495, A8.
  5. ^ a b c d e f Fossati, L.; et al. (December 2007), "Late stages of the evolution of A-type stars on the main sequence: comparison between observed chemical abundances and diffusion models for 8 Am stars of the Praesepe cluster", Astronomy and Astrophysics, 476 (2): 911–925, arXiv:0710.0579, Bibcode:2007A&A...476..911F, doi:10.1051/0004-6361:20078320.
  6. ^ "40 Cnc". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2019-03-03.
  7. ^ a b Andrievsky, Sergei. M. (June 1998), "Blue stragglers in open clusters. I. NGC 2632", Astronomy and Astrophysics, 334: 139−145, Bibcode:1998A&A...334..139A.