U Geminorum
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 AAVSO light curve of U Geminorum's outburst behavior. Different colors reflect different bandpasses. Day numbers are Julian Day. |
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| Observation data Equinox J2000.0 |
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|---|---|
| Constellation | Gemini |
| Right ascension | 07h 55m 05.2s |
| Declination | +22° 00′ 04″ |
| Apparent magnitude (V) | 14.1-15.0 (quiet), 9.0 (outburst) |
| Characteristics | |
| Spectral type | sd:Be+ / M4.5Ve |
| U-B color index | ? |
| B-V color index | ? |
| Variable type | Dwarf nova |
| Astrometry | |
| Radial velocity (Rv) | +37 km/s |
| Proper motion (μ) | RA: -30.0 mas/yr Dec.: -42.2 mas/yr |
| Parallax (π) | ? ± ? mas |
| Distance | ? ly (? pc) |
| Absolute magnitude (MV) | 9.5 |
| Other designations | |
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HD 64511
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U Geminorum, 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. Roughly every 100 days it undergoes an outburst that greatly increases its brightness. Discovered by J.R. Hind in 1855 during one of its outbursts, it has been continuously observed since.
The U Geminorum binary has a very short orbital period of 4 hours and 11 minutes; this orbit alone makes the system variable, as the components transit and eclipse each other with each revolution. Normally, the combined apparent magnitude varies between 14.0 and 15.1; during an outburst however, the star can brighten a hundredfold, to 9th magnitude. Though the average interval is 100 days, the period is in fact highly irregular, varying from as little as 62 days to as long as 257. As is the case with dwarf novae, the outbursts are theorized results of a periodic surge of influx from the white dwarf's accretion disk, caused by instability in the disk itself.
[edit] See also
- SS Cygni
[edit] References
- AAVSO: "U Gem: February 1999 Variable Star of the Month." (Accessed 5/19/06)
- Burnham, Robert. Burnham's Celestial Handbook. New York: Dover Publications, Inc., 1978. ISBN 0-486-23568-8 pp. 925-34.
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