Omega Ursae Majoris

Omega Ursae Majoris (Omega UMa, ω Ursae Majoris, ω UMa) is a binary star system in the northern circumpolar constellation of Ursa Major. It is visible to the naked eye with an apparent visual magnitude of 4.61.^[2] Based upon an annual parallax shift of 13.24 mas,^[1] it is roughly 246 light years from the Sun. At that distance, the visual magnitude of the star is diminished by an extinction factor of 0.11 due to interstellar dust.^[6]

ω Ursae Majoris

Location of ω Ursae Majoris (circled)
Observation data Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation	Ursa Major
Right ascension	10h 53m 58.74035s[1]
Declination	+43° 11′ 23.8483″[1]
Apparent magnitude (V)	4.61[2]
Characteristics
Spectral type	A1VsSi:[3] or A0 IV−V[4]
U−B color index	−0.11[2]
B−V color index	−0.04[2]
Astrometry
Radial velocity (Rv)	−18.70±0.80[5] km/s
Proper motion (μ)	RA: +42.97[1] mas/yr Dec.: −23.62[1] mas/yr
Parallax (π)	13.24±0.50 mas[1]
Distance	246 ± 9 ly (76 ± 3 pc)
Absolute magnitude (MV)	+0.86[6]
Orbit[7]
Period (P)	15.8307 d
Eccentricity (e)	0.31
Periastron epoch (T)	2435185.246 JD
Argument of periastron (ω) (secondary)	27.3°
Semi-amplitude (K1) (primary)	22.2 km/s
Details
Radius	2.5[8] R☉
Luminosity	76[9] L☉
Surface gravity (log g)	3.88[4] cgs
Temperature	9,647[9] K
Rotational velocity (v sin i)	47[10] km/s
Age	325[6] Myr
Other designations
ω UMa, 45 Ursae Majoris, BD+43°2058, FK5 2870, HD 94334, HIP 53295, HR 4248, SAO 43512[11]
Database references
SIMBAD	data

This is a single-lined spectroscopic binary star system with an orbital period of 15.8 days and an eccentricity of 0.31.^[7] The primary member, component A, is an A-type main sequence star with a stellar classification of A1VsSi:.^[3] The stellar spectrum has the appearance of a hot Am star, showing overabundances of many iron-peak and heavier elements, but an underabundance of helium.^[12] In particular, it has an abnormal abundance of silicon.^[13]

Naming

In Chinese, 天牢 (Tiān Láo), meaning Celestial Prison, refers to an asterism consisting of ω Ursae Majoris, 57 Ursae Majoris, 47 Ursae Majoris, 58 Ursae Majoris, 49 Ursae Majoris and 56 Ursae Majoris. Consequently, the Chinese name for ω Ursae Majoris itself is 天牢一 (Tiān Láo yī, English: the First Star of Celestial Prison.).^[14]