Theta1 Crucis

For other stars with the name θ Crucis, see Theta Crucis.

Theta¹ Crucis (θ¹ Cru, Theta¹ Crucis) is a spectroscopic binary star system in the southern constellation of Crux. It is visible to the naked eye with an apparent visual magnitude of 4.30^m.^[2] The distance to this star, as determined using parallax measurements,^[1] is around 235 light years.

θ¹ Crucis

Observation data Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation	Crux
Right ascension	12h 03m 01.50130s[1]
Declination	−63° 18′ 46.5406″[1]
Apparent magnitude (V)	4.30[2]
Characteristics
Spectral type	A3(m)A8-A8[3]
U−B color index	+0.03[2]
B−V color index	+0.28[2]
Astrometry
Radial velocity (Rv)	−2.4[4] km/s
Proper motion (μ)	RA: −152.35[1] mas/yr Dec.: +7.00[1] mas/yr
Parallax (π)	13.88±0.15 mas[1]
Distance	235 ± 3 ly (72.0 ± 0.8 pc)
Absolute magnitude (MV)	+1.29[5]
Orbit[6]
Period (P)	24.4828 d
Eccentricity (e)	0.61
Periastron epoch (T)	2419453.3470 JD
Argument of periastron (ω) (secondary)	358.9°
Semi-amplitude (K1) (primary)	46.1 km/s
Semi-amplitude (K2) (secondary)	56.1 km/s
Details
Mass	1.57[7] M☉
Luminosity	81[8] L☉
Surface gravity (log g)	3.76[7] cgs
Temperature	7341±250[7] K
Age	1.1[7] Gyr
Other designations
θ1 Cru, CPD−62° 2543, HD 104671, HIP 58758, HR 4599, SAO 251705.[9]
Database references
SIMBAD	data

The pair orbit each other closely with a period of 24.5 days and an eccentricity of 0.61.^[6] The primary component is an Am star, which is a chemically peculiar A-type star that shows anomalous variations in absorption lines of certain elements.^[10] It has a stellar classification of A3(m)A8-A8.^[3] With a mass 157% times that of the Sun,^[7] it radiates 81^[8] times the Sun's luminosity from its outer atmosphere at an effective temperature of 7341 K.^[7] Unusually for a fully radiative A-type star, X-ray emissions have been detected, which may instead be coming from the orbiting companion.^[11]