dwarf novae

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dwarf novae

A small group of intrinsically faint stars that are characterized by sudden increases in brightness occurring at intervals of a few weeks or months, the maximum brightness lasting only a few days. The change in brightness (i.e. amplitude) is usually between 2–5 magnitudes. The first to be discovered, U Geminorum, is typical of the majority, which are therefore classified as U Geminorum stars . This subgroup displays a fairly smooth decline in brightness from the maximum, unlike the much smaller subgroup of Z Camelopardalis stars that can undergo standstills, i.e. periods of nearly constant intermediate brightness, before dropping to minimum brightness. Both the occurrence of the standstill and its duration – a few days to many months – are quite unpredictable. There are also periods of erratic light variations. SU Ursae Majoris stars , another subgroup, differ from U Gem stars by occasionally having particularly long outbursts – superoutbursts – that are brighter than normal outbursts.

Dwarf novae are a class of cataclysmic variables, i.e. close binary stars in which the primary is a white dwarf. The secondary is a cooler main-sequence star, spectral type K or G. The components have similar masses (about 0.7 to 1.2 solar masses); the orbital periods are between about 3 to 15 hours. There are two popular models for dwarf novae. In the mass-transfer instability model, the secondary is undergoing irregular expansion and episodically fills its Roche lobe (see equipotential surfaces. Hydrogen-rich gas then streams from the secondary and takes up a disk-shaped orbit around the primary, ultimately leading to an outburst. In the more popular disk instability model, the outbursts are caused by episodically recurring thermal instabilities in the accretion disk (see mass transfer), which is continually being fed by mass transfer from the Roche-lobe filling secondary. The outburst itself does not involve an explosion, and no significant amount of mass is ejected. The gas in the disk spirals down on to the white dwarf, where it may eventually cause a nova explosion.

dwarf novae

[¦dwȯrf ′nō‚vī]
(astronomy)
A class of irregular variable stars which undergo rapid increases in brightness of several magnitudes at semiperiodic intervals, and then decrease more slowly to the normal minimum; they may be divided into U Geminorum stars and Z Camelopardalis stars.
References in periodicals archive ?
2) who also reported the first observed outburst of the system, confirming it to be a dwarf nova.
Among specific topics are observational population studies of the variables, faint X-ray sources in globular clusters in the XMM-Newton and Chandra era, jets and outflows in micro-quasars, a model for low accretions rate polars, the spreading layer and dwarf nova oscillations, correlated X-ray and optical variability in X-ray binaries, and white dwarfs undergoing hydrogen shell burning single degenerate binary systems.
SUZAKU observations of the Dwarf Nova V893 Scorpii: The Discovery of a Partial X-ray Eclipse.
As those who follow reports of their outbursts in this Journal may recall, a dwarf nova comprises a very small, dense, hot white dwarf star whose strong gravitational field is drawing gas, mainly hydrogen, from a closely orbiting cooler and larger red star.
Title: Photometric Studies of a WZ Sge-Type Dwarf Nova Candidate, ASAS 160048-4846.
The 2011 February superoutburst of the dwarf nova SDSS J112003.
This dwarf nova of the ugwz class performed over months and CBA Pretoria, having suitably clear winter nights, contributed extensively, eg much more than any other observatory.
Their subsequent investigations showed that rather than being a flare star, V1212 Tau is a dwarf nova of the SU UMa family.
It would be 40 years before another dwarf nova would be identified, and 93 years would pass before flickering would be accepted as a genuine phenomenon.
3) subsequently identified it as a dwarf nova during the course of the Sloan Digital Sky Survey, calling it SDSS J015151.
Superoutbursts of the SU UMa-type dwarf nova CP Draconis', J.