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40 Cancri
Observation data; Epoch J2000.0 Equinox J2000.0
Constellation	Cancer
Right ascension	08h 40m 11.45280s
Declination	+19° 58′ 16.0852″
Apparent magnitude (V)	6.61
Characteristics
Evolutionary stage	main sequence
Spectral type	A1 V
B−V color index	0.006±0.005
Astrometry
Radial velocity (Rv)	+34.4±0.6 km/s
Proper motion (μ)	RA: −35.312 mas/yr ; Dec.: −13.595 mas/yr
Parallax (π)	5.2065 ± 0.0713 mas
Distance	626 ± 9 ly ; (192 ± 3 pc)
Absolute magnitude (MV)	0.32
Details
Mass	2.46±0.12 M☉
Radius	2.72±0.12 R☉
Luminosity	73.68 L☉
Surface gravity (log g)	3.78 cgs
Temperature	9,382 K
Rotational velocity (v sin i)	10 km/s
Other designations
	40 Cnc, BD+20°2159, HD 73666, HIP 42523, SAO 80336, WDS J08401+2000
Database references
SIMBAD	data

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]

References

^ ^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.
^ ^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, S2CID 119257644.
^ ^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.
^ ^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: A8, arXiv:0911.1874, Bibcode:2010A&A...510A...8F, doi:10.1051/0004-6361/200811495, S2CID 118658470, A8.
^ ^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, S2CID 16152096.
^ "40 Cnc". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2019-03-03.
^ ^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.