Tau Persei
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Perseus |
| Right ascension | 02h 45m 15.46108s |
| Declination | +52° 45′ 44.9240″ |
| Apparent magnitude (V) | 3.94 - 4.07 |
| Characteristics | |
| U−B color index | +0.46 |
| B−V color index | +0.74 |
| Variable type | Algol |
| τ Per A | |
| Spectral type | G8 IIIa |
| U−B color index | +0.68 |
| B−V color index | +0.91 |
| τ Per B | |
| Spectral type | A3-4 V |
| U−B color index | +0.07 |
| B−V color index | +0.15 |
| Astrometry | |
| Radial velocity (Rv) | 2.2 ± 0.7 km/s |
| Proper motion (μ) | RA: −1.26 mas/yr Dec.: −4.37 mas/yr |
| Parallax (π) | 12.83±0.36 mas |
| Distance | 254 ± 7 ly (78 ± 2 pc) |
| Absolute magnitude (MV) | −0.65 −0.45 / 1.26 |
| Orbit | |
| Period (P) | 4.149 yr |
| Semi-major axis (a) | 0.055 |
| Eccentricity (e) | 0.728 |
| Inclination (i) | 94.5° |
| Longitude of the node (Ω) | 100.6° |
| Periastron epoch (T) | B 2013.888 |
| Argument of periastron (ω) (secondary) | 54.1° |
| Details | |
| τ Per A | |
| Mass | 2.99 ± 0.10 M☉ |
| Radius | 16.08 ± 0.54 R☉ |
| Luminosity | 191 L☉ |
| Surface gravity (log g) | 2.47 ± 0.03 cgs |
| Temperature | 5507 ± 83 K |
| Metallicity [Fe/H] | −0.20 ± 0.03 dex |
| Age | 0.39 ± 0.05 Gyr |
| τ Per B | |
| Mass | 1.8 M☉ |
| Radius | 2.2 R☉ |
| Temperature | 8970 ± 150 K |
| Other designations | |
| 18 Per, BD+52°641, HD 17878, HD 17879, HIP 13531, HR 854, SAO 23685 | |
| Database references | |
| SIMBAD | data |
Tau Persei (τ Per), also known as 18 Persei, is a binary star in the constellation of Perseus. The system is fairly close, and is located about 254 light-years (78 parsecs) away, based on its parallax.
Tau Persei is an eclipsing binary, which means the two stellar components orbit each other in such an orientation that they periodically eclipse each other, while blocking the other's light. Unlike many eclipsing binaries that have short orbital periods, Tau Persei has an orbital period of 4.15 years. With a semi-major axis of 0.055 arcseconds, this is one of the few eclipsing binaries whose components can be resolved with interferometry.
The primary component of Tau Persei is a red giant with a spectral type of G8III. It has a radius 16 times that of the Sun, and is about 390 million years old. Its companion is an A-type main-sequence star. In 1989, the primary star eclipsed the secondary, allowing for the stellar parameters to be derived via its light curve.