U Geminorum
U Geminorum (U Gem), in the constellation Gemini, is an archetypal example of a dwarf nova. The binary star system consists of a white dwarf closely orbiting a red dwarf. Every few months it undergoes an outburst that greatly increases its brightness. The dwarf nova class of variable stars are often referred to as U Geminorum variables after this star.
AAVSO light curve of U Geminorum's outburst behavior. Different colors reflect different bandpasses. Day numbers are Julian day. | |
| Observation data Epoch J2000.0 Equinox J2000.0 | |
|---|---|
| Constellation | Gemini |
| Right ascension | 07h 55m 05.24s |
| Declination | +22° 00′ 05.1″ |
| Apparent magnitude (V) | 8.2 - 14.9 |
| Characteristics | |
| Spectral type | DA + M4.5Ve |
| Variable type | U Gem + eclipsing |
| Astrometry | |
| Radial velocity (Rv) | +42.0 km/s |
| Proper motion (μ) | RA: −27.363±0.049 mas/yr Dec.: −40.398±0.027 mas/yr |
| Parallax (π) | 10.7121 ± 0.0299 mas |
| Distance | 304.5 ± 0.8 ly (93.4 ± 0.3 pc) |
| Orbit | |
| Primary | White dwarf |
| Companion | Red dwarf |
| Period (P) | 0.1769062 days |
| Semi-major axis (a) | 1.55±0.02 R☉ |
| Eccentricity (e) | 0.027 |
| Inclination (i) | 69.7±0.7° |
| Semi-amplitude (K1) (primary) | 107±2 km/s |
| Semi-amplitude (K2) (secondary) | 310±5 km/s |
| Details | |
| White dwarf | |
| Mass | 1.2±0.05 M☉ |
| Radius | 0.008 R☉ |
| Surface gravity (log g) | 7.90 cgs |
| Temperature | 29,200 K |
| Red dwarf | |
| Mass | 0.42±0.04 M☉ |
| Radius | 0.43±0.06 R☉ |
| Other designations | |
U Gem, BD+22 1807, HD 64511. | |
| Database references | |
| SIMBAD | data |
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