Theta Carinae
 Location of θ Carinae (circled) |
|
| Observation data Epoch J2000.0 Equinox J2000.0 |
|
|---|---|
| Constellation | Carina |
| Right ascension | 10h 42m 57.40197s |
| Declination | –64° 23′ 40.0208″ |
| Apparent magnitude (V) | 2.76 |
| Characteristics | |
| Spectral type | B0.5 Vp |
| U−B color index | –1.00 |
| B−V color index | –0.22 |
| Astrometry | |
| Radial velocity (Rv) | +24 km/s |
| Proper motion (μ) |
RA: –18.36 mas/yr Dec.: +12.03 mas/yr |
| Parallax (π) | 7.16 ± 0.21mas |
| Distance | 460 ± 10 ly (140 ± 4 pc) |
| Orbit | |
| Period (P) | 2.20288 ± 0.00001 d |
| Eccentricity (e) | 0.129 ± 0.002 |
|
Argument of periastron (ω) (secondary) |
81.8 ± 1.7° |
|
Semi-amplitude (K1) (primary) |
18.93 ± 0.05 km/s |
| Details | |
| θ Car A | |
| Mass | 14.9 ± 0.4 M☉ |
| Radius | 5.1 R☉ |
| Luminosity | 25,673 L☉ |
| Surface gravity (log g) | 4.20 cgs |
| Temperature | 31,000 K |
| Rotational velocity (v sin i) | 108 ± 3 km/s |
| Age | 4.0 ± 0.7 Myr |
| Other designations | |
Theta Carinae (θ Car, θ Carinae) is a star in the southern constellation of Carina. With an apparent visual magnitude of 2.76, it is the brightest star in the open star cluster IC 2602. It marks the northeastern end of the Diamond Cross asterism. Parallax measurements from the Hipparcos mission place this star at a distance of about 460 light-years (140 parsecs) from Earth.
In Chinese, 南船 (Nán Chuán), meaning Southern Boat, refers to an asterism consisting of θ Carinae, V337 Carinae, PP Carinae, β Carinae and ω Carinae. Consequently, θ Carinae itself is known as 南船三 (Nán Chuán sān, English: the Third Star of Southern Boat.)
The stellar classification of this star is B0.5 Vp, which indicates this is a B-type main sequence star that is generating energy at its core through the nuclear fusion of hydrogen. The 'p' suffix means it displays peculiar features in its spectrum, which have been observed in both the optical and ultraviolet band. This might be explained by a magnetic field, yet no such measurable field has been observed. Theta Carinae is actually a single-lined spectroscopic binary with a period of 2.2 days; the shortest known orbital period among massive stars. The close orbit means that a mass transfer between the two components may have occurred, which could explain the peculiarities of the spectrum.
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