Theta Pegasi
| Observation data Epoch J2000.0 Equinox J2000.0 | |
|---|---|
| Constellation | Pegasus |
| Right ascension | 22h 10m 11.98528s |
| Declination | +06° 11′ 52.3078″ |
| Apparent magnitude (V) | +3.52 |
| Characteristics | |
| Evolutionary stage | main sequence |
| Spectral type | A2V + M4-5.5 |
| B−V color index | 0.086±0.002 |
| Astrometry | |
| Radial velocity (Rv) | −7.9±2.4 km/s |
| Proper motion (μ) | RA: +282.18 mas/yr Dec.: +30.46 mas/yr |
| Parallax (π) | 35.34±0.85 mas |
| Distance | 92 ± 2 ly (28.3 ± 0.7 pc) |
| Absolute magnitude (MV) | 1.24 |
| Orbit | |
| Semi-major axis (a) | 6.55+3.0 −0.48 au |
| Eccentricity (e) | 0.54+0.28 −0.15 |
| Inclination (i) | 66.7+8.5 −14° |
| Details | |
| θ Peg A | |
| Mass | 2.09 ± 0.16 M☉ |
| Radius | 2.623±0.083 R☉ |
| Luminosity | 23.7±1.1 L☉ |
| Surface gravity (log g) | 3.95 cgs |
| Temperature | 7872±82 K |
| Metallicity [Fe/H] | −0.38 dex |
| Rotational velocity (v sin i) | 136 km/s |
| Age | 448 Myr |
| θ Peg B | |
| Mass | 0.280+0.18 −0.059 M☉ |
| Surface gravity (log g) | 5.5 cgs |
| Temperature | 3200 K |
| Other designations | |
| Biham, θ Peg, 26 Peg, FK5 834, HD 210418, HIP 109427, HR 8450, SAO 127340 | |
| Database references | |
| SIMBAD | data |
θ Pegasi, Latinized as Theta Pegasi, is a single star in the equatorial constellation of Pegasus, lying about 7.5 degrees southwest of Enif. It has the traditional name Biham /ˈbaɪ.æm/, and the Flamsteed designation 26 Pegasi. This object is visible to the naked eye as a white-hued point of light with an apparent visual magnitude of +3.52. The system is located 92 light years from the Sun based on parallax, but is drifting closer with a radial velocity of −8 km/s.
This object an A-type main-sequence star with a stellar classification of A2V. It is 448 million years old with a high rate of spin, showing a projected rotational velocity of 136 km/s. This star has 2.09 times the mass of the Sun and 2.6 times the Sun's radius. It is radiating 25 times the luminosity of the Sun from its outer envelope at an effective temperature of 7,951 K. The star appears to display a slight infrared excess.
θ Pegasi was suspected of being a binary star due to an acceleration detected by Hipparcos. In 2021, a low-mass companion star was discovered, associated with θ Pegasi. It is a red dwarf with a spectral type of M4 to M5.5, and a luminosity of 0.5% that of the Sun. The orbit around the primary is estimated to be moderately eccentric, at 0.54, and has a semimajor axis of 6.55 au.