Theta Geminorum

Theta Geminorum (θ Gem, θ Geminorum) is a single^[12] star in the northern zodiac constellation of Gemini. It is visual to the naked eye with an apparent visual magnitude of 3.59.^[2] Based upon an annual parallax shift of 17.25 mas,^[1] it is about 189 light years distant from the Sun.

θ Geminorum

Observation data Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation	Gemini
Right ascension	06h 52m 47.33887s[1]
Declination	+33° 57′ 40.5175″[1]
Apparent magnitude (V)	3.59[2]
Characteristics
Spectral type	A2 IV[3]
U−B color index	+0.13[2]
B−V color index	+0.10[2]
Astrometry
Radial velocity (Rv)	+21[4] km/s
Proper motion (μ)	RA: −1.66[1] mas/yr Dec.: −47.31[1] mas/yr
Parallax (π)	17.25±0.19 mas[1]
Distance	189 ± 2 ly (58.0 ± 0.6 pc)
Absolute magnitude (MV)	−0.18[5]
Details
Mass	1.80[6] M☉
Radius	5.1[7] R☉
Luminosity	93[8] L☉
Surface gravity (log g)	3.40±0.14[6] cgs
Temperature	8,502±289[6] K
Rotational velocity (v sin i)	133[9] km/s
Age	252[6] Myr
Other designations
θ Gem, The Gem,[10] 34 Gem, BD+34°1481, FK5 261, HD 50019, HIP 33018, HR 2540, SAO 59570.[11]
Database references
SIMBAD	data

This is an evolving A-type subgiant star with a stellar classification of A2 IV.^[3] It has 1.80^[6] times the mass of the Sun and radiates 93^[8] times the solar luminosity. The measured angular diameter is 0.82±0.03 mas.^[13] At an estimated distance of this star, this yields a physical size of about 5.1 times the radius of the Sun.^[7] It is around 252 million years old and has a projected rotational velocity of 133^[9] km/s. This rotation rate is giving the star an oblate shape, with an equatorial bulge that is 11% larger than the polar radius.^[14]

The Washington Visual Double Star Catalog lists five visual companions within 100″; the closest and brightest such companion is the magnitude 8.6 θ Geminorum E at an angular separation of 2.4″ along a position angle of 295°, as of 2010.^[15]