Xi1 Canis Majoris

For other star systems with this Bayer designation, see Xi Canis Majoris.
ξ1 Canis Majoris
Location of ξ1 Canis Majoris (circled)
Observation data
Epoch J2000.0      Equinox J2000.0
Constellation Canis Major
Right ascension 06h 31m 51.36636s[1]
Declination −23° 25′ 06.3181″[1]
Apparent magnitude (V) 4.33 – 4.36[2]
Characteristics
Spectral type B1 III[3]
U−B color index −0.98[4]
B−V color index −0.24[4]
Variable type β Cep[3]
Astrometry
Radial velocity (Rv)+26.9[5] km/s
Proper motion (μ) RA: −2.91[1] mas/yr
Dec.: +6.22[1] mas/yr
Parallax (π)2.36 ± 0.20 mas[1]
Distance1,400 ± 100 ly
(420 ± 40 pc)
Absolute magnitude (MV)−3.86[6]
Details
Mass14.2±0.4[6] M☉
Radius7.9±0.6[6] R☉
Luminosity30,900+8,900
−6,900[6] L☉
Surface gravity (log g)3.78±0.07[6] cgs
Temperature27,000±1,000[6] K
Metallicity [Fe/H]−0.18[7] dex
Rotational velocity (v sin i)0[6] km/s
Age11.1±0.7[6] 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
Database references
SIMBADdata

Xi1 Canis Majoris, Latinized from ξ1 Canis Majoris, is a Beta Cephei variable star in the constellation Canis Major. It is approximately 1,400 light years from Earth.

ξ1 Canis Majoris is a blue-white B-type star. It has generally been assigned a luminosity class of III (giant) or IV (subgiant), for example B1III[3] or B0.5IV.[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.[6]

A light curve for Xi1 Canis Majoris, plotted from TESS data[8]

The apparent magnitude varies from +4.33 to +4.36 with a period of 5.03 hours.[2] Its pulsations cause its radius to vary by 1.0% to 1.5%. At the same time its effective temperature by about 500 K above and below its mean temperature.[6]

ξ1 Canis Majoris has the longest known rotation period of any B class star, taking around 30 years to complete one revolution on its axis.[9] 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.[6]

ξ1 Canis Majoris 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 about 27″ away.[10] 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 invisible against the brighter primary.[6]

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