15 Canis Majoris

15 Canis Majoris is a variable star in the southern constellation of Canis Major,^[8] located roughly 1,200 light years away from the Sun.^[2] It has the variable star designation EY Canis Majoris; 15 Canis Majoris is the Flamsteed designation. The star is visible to the naked eye as a faint, blue-white hued star with a baseline apparent visual magnitude of +4.82.^[3] It is moving away from the Earth with a heliocentric radial velocity of 28 km/s.^[7]

15 Canis Majoris

A visual band light curve for EY Canis Majoris (1992)[1]
Observation data Epoch J2000.0      Equinox J2000.0
Constellation	Canis Major
Right ascension	06h 53m 32.907s[2]
Declination	−20° 13′ 27.32″[2]
Apparent magnitude (V)	+4.82[3]
Characteristics
Spectral type	B1 Ib[4]
U−B color index	-0.96[5]
B−V color index	−0.212±0.013[3]
Variable type	β Cep[4][6]
Astrometry
Radial velocity (Rv)	28.00[7] km/s
Proper motion (μ)	RA: −5.46±0.16[2] mas/yr Dec.: +3.58±0.17[2] mas/yr
Parallax (π)	2.68±0.24 mas[2]
Distance	1,200 ± 100 ly (370 ± 30 pc)
Absolute magnitude (MV)	−3.02[3]
Details[4]
Mass	12.8±1.2 M☉
Radius	6.8±1.2 R☉
Luminosity	20,000+12,000 −7,400 L☉
Surface gravity (log g)	3.89±0.20 cgs
Temperature	26,100±1,200 K
Rotational velocity (v sin i)	20±12 km/s
Other designations
15 CMa, EY CMa, BD−20°1616, FK5 2532, GC 9034, HD 50707, HIP 33092, HR 2571, SAO 172520[8]
Database references
SIMBAD	data

This is a B-type supergiant star with a stellar classification of B1 Ib.^[4] Merle F. Walker discovered that 15 Canis Majoris is a variable star in 1955, and he published that discovery in 1956.^[9] It is classified as a Beta Cephei type variable star and its brightness varies from magnitude +4.79 down to +4.84 with a period of 4.430 h.^[6] The star has 12.8 times the mass of the Sun and 6.8 times the Sun's radius. It is radiating 20,000 times the luminosity of the Sun from its photosphere at an effective temperature of 26,100 K.^[4]