45 Cancri

For other stars with this Bayer designation, see A 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]

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 mas[1]
Distance	680 ± 10 ly (210 ± 5 pc)
Absolute magnitude (MV)	−1.62[2]
Orbit[4]
Period (P)	1,009.36±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
Mass	3.11±0.10[3] M☉
Radius	13.86+5.03 −1.73[1] R☉
Luminosity	210.3±5.4[1] L☉
Surface gravity (log g)	2.72[5] cgs
Temperature	5,058[5] K
Metallicity [Fe/H]	−0.69±0.22[5] dex
Rotational velocity (v sin i)	5.3[6] km/s
45 Cnc B
Mass	3.00±0.10[3] M☉
Luminosity	190.5+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
SIMBAD	data

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 K.^[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]