Theta Andromedae
Theta Andromedae is a binary star system in the northern constellation of Andromeda. Theta Andromedae, Latinized from θ Andromedae, is its Bayer designation. It is located at a distance of approximately 173 light-years (53 parsecs) from the Sun, and has an apparent visual magnitude of 4.6. On the Bortle Dark-Sky Scale, this makes it visible to the naked eye from outside urban regions. Based on its motion through space, this system appears to be a member of the Sirius supercluster.
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Andromeda |
| Right ascension | 00h 17m 05.50236s |
| Declination | +38° 40′ 53.8886″ |
| Apparent magnitude (V) | 4.61 |
| Characteristics | |
| Evolutionary stage | main sequence |
| Spectral type | A2 V |
| U−B color index | +0.05 |
| B−V color index | +0.06 |
| Variable type | Constant |
| Astrometry | |
| Radial velocity (Rv) | 0.9 km/s |
| Proper motion (μ) | RA: −57.551(307) mas/yr Dec.: −14.795(155) mas/yr |
| Parallax (π) | 18.8747 ± 0.4251 mas |
| Distance | 173 ± 4 ly (53 ± 1 pc) |
| Absolute magnitude (MV) | −0.25 |
| Orbit | |
| Period (P) | 1033+91 −77 days |
| Semi-major axis (a) | 25+32 −13 mas |
| Eccentricity (e) | 0.95+0.04 −0.40 |
| Inclination (i) | 69+8 −22° |
| Longitude of the node (Ω) | 263+50 −156° |
| Periastron epoch (T) | 238+343 −143 |
| Argument of periastron (ω) (secondary) | 89+175 −29° |
| Details | |
| A | |
| Mass | 2.83±0.08 M☉ |
| Luminosity | 113 L☉ |
| Surface gravity (log g) | 3.95 cgs |
| Temperature | 8,960 K |
| Metallicity [Fe/H] | +0.14 dex |
| Rotational velocity (v sin i) | 102 km/s |
| Other designations | |
| Database references | |
| SIMBAD | data |
The brighter component is a white hued A-type main-sequence star with a stellar classification of A2 V. It is one of the least photometrically variable stars known. The star shows a high rate of rotation with a projected rotational velocity of 102 km/s. It has an estimated 2.8 times the mass of the Sun and is radiating 113 times the Sun's luminosity from its photosphere at an effective temperature of 8,960 K. The relatively high chemical abundances of iron and heavier elements suggests it may be a fast rotating Am star.
A stellar companion was detected in 1986 and reported in 1989. This fainter companion is separated from Theta Andromedae by 0.06 arcseconds. The secondary appears to be a massive, possibly A-type, star orbiting at a distance of around one astronomical unit with a period of 2.83 years and a large orbital eccentricity (ovalness) of 0.95.