Alpha Cancri

Alpha Cancri is a star system in the northern constellation of Cancer. Its name is a Bayer designation that is Latinized from α Cancri, and abbreviated Alpha Cnc or α Cnc. The primary component has the proper name Acubens, pronounced /ˈækjuːbɛnz/.^[12] It forms a fourth-magnitude star with an apparent magnitude of 4.20, making it barely visible to the naked eye under good viewing conditions. Based on parallax measurements, it is located at a distance of 178 light-years (55 pc) from the Sun, but is drifting closer with a radial velocity of −12 km/s.^[6] Since it is near the ecliptic, it can be occulted by the Moon.^[13]

α Cancri

α Cancri, circled, is the bottom left star in the "crab".
Observation data Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation	Cancer[1]
Right ascension	08h 58m 29.2042s[2]
Declination	+11° 51′ 27.649″[2]
Apparent magnitude (V)	4.20 to 4.27[3]
Characteristics
Spectral type	kA7VmF0/2III/IVSr[4]
U−B color index	+0.15[5]
B−V color index	+0.14[5]
R−I color index	+0.04[5]
Astrometry
Radial velocity (Rv)	−12.1±0.8[6] km/s
Proper motion (μ)	RA: 42.181 mas/yr[2] Dec.: −31.160 mas/yr[2]
Parallax (π)	18.3304±0.3216 mas[2]
Distance	178 ± 3 ly (54.6 ± 1.0 pc)
Absolute magnitude (MV)	0.46[1]
Details
A
Mass	2.10[7] M☉
Radius	3.655[8] R☉
Luminosity	49[8] L☉
Surface gravity (log g)	3.73[9] cgs
Temperature	7,943[9] K
Rotational velocity (v sin i)	75[10] km/s
B
Mass	0.38[7] M☉
Other designations
Acubens, Sertan, Sartan[5], α Cnc, Alpha Cancri, Alpha Cnc, 65 Cancri, 65 Cnc, BD+12 1948, FK5 337, GC 12406, HD 76756, HIP 44066, HR 3572, SAO 98267, PPM 125972, ADS 7115 A, CCDM J08585+1151A[11]
Database references
SIMBAD	data
	B

Properties

The primary component, α Cancri A, has a stellar classification of kA7VmF0/2III/IVSr, indicating an Am star with calcium K-lines similar to an A7 main sequence star and hydrogen lines more like an F0 giant or subgiant star. It is a white A-type main-sequence star with an apparent magnitude of +4.26. The star has 2.10^[7] times the mass of the Sun and 3.7^[8] times the Sun's radius. It has a high rate of spin, showing a projected rotational velocity of 75 km/s.^[10] The star is radiating 49 times the luminosity of the Sun from its photosphere at an effective temperature of 7,943 K.^[9]

Its companion, α Cancri B, is an eleventh-magnitude star. In the year 1836, its position angle was observed at 325 degrees with a separation from the main star α Cancri A of 11.3 arcseconds.^[14][15] α Cancri A may itself be a close binary, consisting of two stars with similar brightness and a separation of 0.1 arcsecond, though this is questioned.^[5] Indeed, a light curve generated during a 2014 lunar occultation failed to demonstrate a close companion.^[13]

Nomenclature

α Cancri (Latinised to Alpha Cancri) is the star's Bayer designation.

The traditional name Acubens (Açubens) is derived from the Arabic الزبانى al zubanāh, 'the claws'.^[16] A second name, Sertan /ˈsɜːrtæn/, derives from the Arabic al-saraṭān, 'the crab'. The International Astronomical Union Working Group on Star Names (WGSN) choose 'Acubens' as the proper name for the primary component of this star.^[17]

In modern culture

USS Acubens (AKS-5) was a United States Navy ship.