Xi1 Canis Majoris

For other star systems with this Bayer designation, see Xi Canis Majoris.

Xi¹ Canis Majoris is a blue-white variable star in the constellation Canis Major. Its name is a Bayer designation that is Latinized from ξ¹ Canis Majoris, and abbreviated Xi¹ CMa or ξ¹ CMa. This star is visible to the naked eye with an apparent visual magnitude of +4.3.^[3] Based on an annual parallax shift of 2.17 mas,^[2] it is located at a distance of approximately 1,510 light-years (460 pc) from Earth.

ξ¹ Canis Majoris

Location of ξ1 Canis Majoris (circled)
Observation data Epoch J2000.0      Equinox J2000.0
Constellation	Canis Major[1]
Right ascension	06h 31m 51.366s[2]
Declination	−23° 25′ 06.32″[2]
Apparent magnitude (V)	4.33 to 4.36[3]
Characteristics
Evolutionary stage	main sequence[4]
Spectral type	B1III[5] or B0.7IV[6]
U−B color index	−0.98[7]
B−V color index	−0.24[7]
Variable type	β Cep[5]
Astrometry
Radial velocity (Rv)	+26.9[8] km/s
Proper motion (μ)	RA: −3.352 mas/yr[2] Dec.: +6.157 mas/yr[2]
Parallax (π)	2.1660±0.1257 mas[2]
Distance	1,510 ± 90 ly (460 ± 30 pc)
Absolute magnitude (MV)	−3.86[4]
Details
Mass	14.2±0.4[4] M☉
Radius	7.9±0.6[4] R☉
Luminosity	30,900+8,900 −6,900[4] L☉
Surface gravity (log g)	3.78±0.07[4] cgs
Temperature	27,000±1,000[4] K
Metallicity [Fe/H]	−0.18[1] dex
Rotational velocity (v sin i)	0[4] km/s
Age	11.1±0.7[4] Myr
Other designations
ξ1 CMa, 4 Canis Majoris, CD−23°3991, GC 8496, HD 46328, HIP 31125, HR 2387, SAO 171895, ADS 5176, CCDM 06319-2325[9]
Database references
SIMBAD	data

Properties

The stellar classification of Xi¹ Canis Majoris matches an early-type B-type star. It has generally been assigned a luminosity class of III (giant) or IV (subgiant), for example B1III^[5] or B0.5IV.^[4][6] Comparison of its properties with model evolutionary tracks suggest that it is a main sequence star about three quarters of the way through its main sequence lifetime.^[4] Its estimated age is 11 million years.^[4] This is a massive star with 14 times the mass of the Sun and 8 times the Sun's radius.^[4] It is radiating 30,900^[4] times the luminosity of the Sun from its photosphere at an effective temperature of 27,000 K.^[4]

A light curve for Xi¹ Canis Majoris, plotted from TESS data^[10]

ξ¹ Canis Majoris is classified as a Beta (β) Cephei variable that ranges from magnitude +4.33 to +4.36 with a period of 5.03 hours.^[3] This period has remained very stable, changing by no more than one second per century.^[11] Its pulsations cause its radius to vary by 1.0% to 1.5%. At the same time its effective temperature varies by about 500 K above and below its mean temperature.^[4]

It has the longest known rotation period of any B class star, taking around 30 years to complete one revolution on its axis.^[12] This is thought to be due to magnetic braking; ξ¹ Canis Majoris has the strongest magnetic field of any β Cephei star and would be expected to spin down completely in around four million years. It also has the strongest and hardest X-ray emission of any β Cephei star.^[4] The X-ray emission varies in phase with the optical pulsations. The stellar wind from ξ¹ Canis Majoris is very weak with a terminal velocity of 700 km/s; the star is losing less than 10⁻¹⁰ M_☉·yr⁻¹.^[11]

This star forms a naked eye pairing with ξ² Canis Majoris a little less than a degree away. The Washington Double Star Catalog lists two 14th magnitude companions at an angular separation of about 27″.^[13] In addition, an unseen close companion is suspected due to some faint emission lines in the spectrum that are best explained by a Be star that is invisible against the brighter primary.^[4]