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U Geminorum
Star in the constellation Gemini / From Wikipedia, the free encyclopedia
Not to be confused with Upsilon 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.
Quick Facts Constellation, Right ascension ...
![]() 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 | |
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Constellation | Gemini |
Right ascension | 07h 55m 05.24s[1] |
Declination | +22° 00′ 05.1″[1] |
Apparent magnitude (V) | 8.2 - 14.9[2] |
Characteristics | |
Spectral type | DA[3] + M4.5Ve[4] |
Variable type | U Gem + eclipsing[2] |
Astrometry | |
Radial velocity (Rv) | +42.0[5] km/s |
Proper motion (μ) | RA: −27.363±0.049[6] mas/yr Dec.: −40.398±0.027[6] mas/yr |
Parallax (π) | 10.7121 ± 0.0299 mas[6] |
Distance | 304.5 ± 0.8 ly (93.4 ± 0.3 pc) |
Orbit[7] | |
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[7] M☉ |
Radius | 0.008[8] R☉ |
Surface gravity (log g) | 7.90[3] cgs |
Temperature | 29,200[3] K |
Red dwarf | |
Mass | 0.42±0.04[7] M☉ |
Radius | 0.43±0.06[8] R☉ |
Other designations | |
U Gem, BD+22 1807, HD 64511.[9] | |
Database references | |
SIMBAD | data |
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