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 ?
The intensity of hydrogen emission in the Hubble images hinted that several of the stars might qualify as cataclysmic variables.
Timeseries Photometry (part or full night) on cataclysmic variables (CVs) Most of the timeseries were done as participation in the CBA around the globe monitoring network and VSNET campaigns.
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The observing program was also expanded, adding Cepheid variables, RV Tauri stars, and various eruptive and cataclysmic variables.
T Pyxidis is a cataclysmic variable star (also called a recurrent nova).
Observations of certain binaries, known as cataclysmic variable stars, will involve a special collaboration with observers on the ground, notes Stachnik.
Research projects that need more amateur attention, professionals said, include asteroid light curves and fast-cadence photometry of old novae and other cataclysmic variable stars.
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.
On most clear nights for the last decade, Dvorak has used his "semi-automated" 10-inch Schmidt-Cassegrain scope and CCD camera to measure eclipsing binaries, RR Lyraes, and cataclysmic variable stars for the AAVSO.
NASSP colloquium series: Prof Warner: Rapid variations in cataclysmic variable stars (30 April)--Dr Bouchard: The evolutionary state of the local Universe (7 May)--Dr Woudt: Large-scale dynamics of galaxies: From the Great Attractor to the Shapley supercluster (14 May)--Prof Fairall: Mapping the local Universe (10 September)--Prof Warner: Pulsations in white dwarfs (17 September)--Dr Holwerda: Dust extinction effects in spiral galaxies (15 October).
08h, and announced the discovery of an intermittent wind outflow--only the second cataclysmic variable (CV) after BZ Cam to show this phenomenon by this time.