U Geminorum
Encyclopedia
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.
Distance estimates for U Geminorum have varied from 52 pc to 112 pc, with a best estimate of 82 pc.
Constellation
In modern astronomy, a constellation is an internationally defined area of the celestial sphere. These areas are grouped around asterisms, patterns formed by prominent stars within apparent proximity to one another on Earth's night sky....
Gemini
Gemini (constellation)
Gemini is one of the constellations of the zodiac. It was one of the 48 constellations described by the 2nd century astronomer Ptolemy and it remains one of the 88 modern constellations today. Its name is Latin for "twins", and it is associated with the twins Castor and Pollux in Greek mythology...
, is an archetypal example of a dwarf nova
Dwarf nova
A U Geminorum-type variable star, or dwarf nova is a type of cataclysmic variable starhttp://www.sai.msu.su/groups/cluster/gcvs/gcvs/iii/vartype.txt consisting of a close binary star system in which one of the components is a white dwarf, which accretes matter from its companion...
. The binary star
Binary star
A binary star is a star system consisting of two stars orbiting around their common center of mass. The brighter star is called the primary and the other is its companion star, comes, or secondary...
system consists of a white dwarf
White dwarf
A white dwarf, also called a degenerate dwarf, is a small star composed mostly of electron-degenerate matter. They are very dense; a white dwarf's mass is comparable to that of the Sun and its volume is comparable to that of the Earth. Its faint luminosity comes from the emission of stored...
closely orbiting a red dwarf
Red dwarf
According to the Hertzsprung-Russell diagram, a red dwarf star is a small and relatively cool star, of the main sequence, either late K or M spectral type....
. 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
Apparent magnitude
The apparent magnitude of a celestial body is a measure of its brightness as seen by an observer on Earth, adjusted to the value it would have in the absence of the atmosphere...
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.
Distance estimates for U Geminorum have varied from 52 pc to 112 pc, with a best estimate of 82 pc.
External links
- AAVSO: U Gem: February 1999 Variable Star of the Month
- animation
- IR spectral data for redshift calculations
- AAVSO: Quick Look View of AAVSO Observations (get recent magnitude estimates for U Gem)