cataclysmic variable

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cataclysmic variable

(kat-ă-kliz -mik) (eruptive variable) A close binary star system where one member is a white dwarf, and mass transfer on to the latter causes sudden large and unpredictable changes in brightness. The main classes of cataclysmic variable are classical novae, recurrent novae, dwarf novae, and symbiotic stars. The outbursts of cataclysmic variables are also detected at ultraviolet and X-ray wavelengths; their X-ray output is however much less than that of X-ray transients, which are similar systems where the compact star is a neutron star rather than a white dwarf.

It is generally believed that the progenitors of cataclysmic variables are wide binaries with periods of several months to several years. When the primary evolves and fills its Roche lobe as a giant, mass is lost from it (see equipotential surfaces); this mass forms a common envelope surrounding the core of the giant (a white dwarf) and the companion. Due to frictional drag, the orbit of the immersed binary shrinks until the envelope is ejected forming a bright planetary nebula and a short-period precataclysmic binary.

The distribution of orbital periods of cataclysmic variables displays a very pronounced gap between 2 and 3 hours, known as the period gap. It is widely believed that the gap is caused by the temporary cessation of mass transfer when the orbital period has decreased to three hours (possibly related to changes in the magnetic field of the mass-losing star when its interior becomes fully convective) so that the system has no longer the appearance of a cataclysmic variable.

cataclysmic variable

[¦kad·ə¦kliz·mik ′ver·ē·ə·bəl]
(astronomy)
A star showing a sudden increase in the magnitude of light, followed by a slow fading of light; examples are novae and supernovae. Also known as explosive variable.
In particular, a short-period binary star, one of whose components is a white dwarf star, capable of irregularly timed but recurrent outbursts of brightness by 2 to 10,000.
References in periodicals archive ?
An AM CVn star, or AM Canum Venaticorum star, is a type of cataclysmic variable star.
Dwarf novae are a class of cataclysmic variable star in which a white dwarf primary accretes material from a secondary star via Roche lobe overflow.
T Pyxidis is a cataclysmic variable star (also called a recurrent nova).
MSc student Zietsman completed his dissertation in 2008 in which he analysed SALT spectroscopy and simultaneous photometry from the SAAO 74-inch telescope, of the eclipsing cataclysmic variable star EC21178-5417.
For his MSc dissertation, Mr Zietsman is analysing SALT spectroscopy and simultaneous photometry from the SAAO 74-in telescope, of the eclipsing cataclysmic variable star EC21178-5417.
Dwarf novae are a type of cataclysmic variable star in which a cool main sequence secondary star loses mass to a white dwarf primary.
Consequently since 2005 the telescope has mainly been used for CCD photometry of cataclysmic variable stars (CVs), particularly dwarf novae.
The participation in this global network has given the Bronberg Observatory additional status as it is also involved in time series studies of active cataclysmic variable stars (CV).
The survey data includes 185 cataclysmic variable stars, which is about three out of every four such objects discovered over the same time span and more than the Sloan Digital Sky Survey found in six years.
Sion is Professor of Astronomy and Astrophysics at Villanova University specializing in white dwarf stars, cataclysmic variable stars, and theoretical accretion physics.
The telescope will be capable of unsupervised, fully autonomous operation for many nights of observations and is ideally suited to monitoring many hundreds of variable astronomical objects such as supernovae, gamma-ray bursters, and cataclysmic variable stars.
Observations of certain binaries, known as cataclysmic variable stars, will involve a special collaboration with observers on the ground, notes Stachnik.