U Pegasi
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Min I: 10.07
Min II: 9.73[4]
| Observation data Epoch J2000.0 Equinox J2000.0 | |
|---|---|
| Constellation | Pegasus[2] |
| Right ascension | 23h 57m 58.477s[3] |
| Declination | +15° 57′ 10.09″[3] |
| Apparent magnitude (V) | 9.23 Min I: 10.07 Min II: 9.73[4] |
| Characteristics | |
| Evolutionary stage | main sequence[5] |
| Spectral type | G2 V + G2: V:[5] |
| B−V color index | 0.648±0.033[2] |
| Variable type | W UMa[6] |
| Astrometry | |
| Radial velocity (Rv) | −28.5±4.7[4] km/s |
| Proper motion (μ) | RA: 34.598 mas/yr[3] Dec.: 17.389 mas/yr[3] |
| Parallax (π) | 5.4708±0.0193 mas[3] |
| Distance | 596 ± 2 ly (182.8 ± 0.6 pc) |
| Absolute magnitude (MV) | 3.88[2] |
| Orbit[5] | |
| Period (P) | 8.995 h |
| Eccentricity (e) | 0 (assumed) |
| Inclination (i) | 76.1[7]° |
| Semi-amplitude (K1) (primary) | 77.6±1.1 km/s |
| Semi-amplitude (K2) (secondary) | 246.5±1.4 km/s |
| Details | |
| Primary | |
| Mass | 1.224±0.003[8] M☉ |
| Radius | 1.149±0.009[8] R☉ |
| Luminosity | 1.29[7] L☉ |
| Surface gravity (log g) | 4.32[8] cgs |
| Temperature | 5,860[8] (polar) K |
| Secondary | |
| Mass | 0.379±0.002[8] M☉ |
| Radius | 0.744±0.002[8] R☉ |
| Luminosity | 0.55[7] L☉ |
| Surface gravity (log g) | 4.27[8] cgs |
| Temperature | 5,785±7[8] (polar) K |
| Other designations | |
| U Peg, BD+15° 4915, HIP 118149, SAO 108933, PPM 143009, WDS J23579+1557A[9] | |
| Database references | |
| SIMBAD | data |
U Pegasi is a binary star system in the constellation of Pegasus, abbreviated U Peg. The pair form an eclipsing binary with a combined peak apparent visual magnitude of 9.23,[4] which is far too faint to be visible to the naked eye. During the primary eclipse the magnitude decreases to 10.07, while the secondary eclipse only drops to magnitude 9.73.[4] This system is located at a distance of approximately 596 light years from the Sun based on parallax measurements, but is drifting closer with a radial velocity of around −28.5 km/s.[4]
The variable luminosity of this system was discovered by S. C. Chandler in 1895. He found it to have a continuously varying light curve with a period of 5.192 h.[10] Observing the star photometrically, in 1898 E. C. Pickering and O. Wendell determined a longer period of 8.995 h.[11] H. Shapley published orbital measures for this eclipsing binary in 1913, estimating their relative luminosities and radii.[12] It was determined to be a variable of the W Ursae Majoris type,[13] and in 1945 the orbital period was shown to vary over time.[14]
