Kappa Canis Majoris

Kappa Canis Majoris is a solitary,^[11] blue-white hued star in the constellation Canis Major. Its name is a Bayer designation that is Latinized from κ Canis Majoris, and abbreviated Kappa CMa or κ CMa. This star is visible to the naked eye with an apparent visual magnitude of +3.87.^[2] Based upon an annual parallax shift of 7.70 mas as seen from Earth,^[1] this star is located about 660 light years from the Sun. It is receding from the Sun with a line of sight velocity of +14 km/s.^[4]

A light curve for Kappa Canis Majoris. The main plot, from Hipparcos data,^[12] shows the long-term variability and the inset plot, from TESS data,^[13] shows the short-term variability.

Kappa Canis Majoris

Location of κ Canis Majoris (circled)
Observation data Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation	Canis Major
Right ascension	06h 49m 50.45933s[1]
Declination	−32° 30′ 30.5225″[1]
Apparent magnitude (V)	+3.87[2]
Characteristics
Spectral type	B1.5 Ve[3]
U−B color index	−0.97[2]
B−V color index	−0.20[2]
Variable type	γ Cas[3]
Astrometry
Radial velocity (Rv)	+14.0±4.1[4] km/s
Proper motion (μ)	RA: −8.84[1] mas/yr Dec.: +3.73[1] mas/yr
Parallax (π)	4.95±0.12 mas[1]
Distance	660 ± 20 ly (202 ± 5 pc)
Absolute magnitude (MV)	−3.03[5]
Details
Mass	12.2±0.3[6] M☉
Radius	5.9[7] R☉
Luminosity (bolometric)	18,876[8] L☉
Surface gravity (log g)	4.07[7] cgs
Temperature	24,600[7] K
Rotational velocity (v sin i)	290±6[9] km/s
Age	13.3±1.2[6] Myr
Other designations
κ CMa, 13 Canis Majoris, CD−32°3404, FK5 1180, GC 8946, HD 50013, HIP 32759, HR 2538, SAO 197258[10]
Database references
SIMBAD	data

This is a massive B-type main-sequence star with a stellar classification of B1.5 Ve,^[3] although Hiltner et al. (1969) classified it as B1.5 IVe^[14] suggesting it is a subgiant star. The 'e' suffix indicates it is a rapidly rotating Be star with a circumstellar decretion disk of heated gas.^[7] The radius of the emitting disk is about 0.20±0.06 AU, or about 3.7 times the radius of the star.^[15] It is classified as a Gamma Cassiopeiae type variable star and its brightness varies from magnitude +3.4 to +3.97.^[3] The star became 50% brighter between 1963 and 1978, increasing from magnitude 3.96 or so to 3.52.^[16]

This star is about 13.3^[6] million years old and spinning with a projected rotational velocity of 290 km/s.^[9] It has 6 times the radius of the Sun and 12 times the Sun's mass. The star is emitting 18,876^[8] times the luminosity of the Sun from its photosphere at an effective temperature of 24,600 K.^[7]

Naming

In Chinese, 弧矢 (Hú Shǐ), meaning Bow and Arrow,^[17] refers to an asterism consisting of κ Canis Majoris, δ Canis Majoris, η Canis Majoris, HD 63032, HD 65456, ο Puppis, k Puppis, ε Canis Majoris and π Puppis. Consequently, κ Canis Majoris itself is known as 弧矢八 (Hú Shǐ bā, English: the Eighth Star of Bow and Arrow.)^[18]