U Geminorum

Not to be confused with Upsilon Geminorum.
U Geminorum

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[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]
Distance304.5 ± 0.8 ly
(93.4 ± 0.3 pc)
Orbit[7]
PrimaryWhite dwarf
CompanionRed 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
Mass1.2±0.05[7] M☉
Radius0.008[8] R☉
Surface gravity (log g)7.90[3] cgs
Temperature29,200[3] K
Red dwarf
Mass0.42±0.04[7] M☉
Radius0.43±0.06[8] R☉
Other designations
U Gem, BD+22 1807, HD 64511.[9]
Database references
SIMBADdata

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.

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