dwarf novae

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 ?
Superhumps were present with a peak-to-peak amplitude of up to ~0.3 mag, thereby confirming the system to be a member of the SU UMa family of dwarf novae. The mean superhump period during the later part of the 2012 outburst was [P.sub.s] = 0.08076(40)d.
This phenomenon, called the thermal-viscous limit cycle, helps astronomers explain transient outbursts across a wide range of systems, from protoplanetary disks around young stars, to dwarf novae -- where the central object is a white dwarf star -- and even bright emission from supermassive black holes in the hearts of distant galaxies.
However this would not have been possible without the use of a modified modern data regularisation technique which allowed the first effective application of a method for accurately determining white dwarf masses in eclipsing dwarf novae. The regularisation technique, and its application to the analysis of other eclipsing compact objects--from albedo mapping of solar system objects, to the detection of rings around extra-solar planets--are briefly discussed.
With a worldwide network of enthusiastic amateurs constantly monitoring 10 dwarf novae for visible outbursts, a team of professionals led by Elmar Kording (Universite Paris Diderot, France) stood a much better chance of catching the elusive jet production in action.
Dwarf novae are interacting binary stars in which a cool main sequence secondary star loses mass to a white dwarf primary.
Carinae and oscillations in dwarf novae in quiescence.
THERE ARE NOVAE, and there are dwarf novae. Despite their similar names, they erupt by completely different mechanisms.
The presence of superhumps is diagnostic that GALEX J215818.5+241924 is a member of the SU UMa family of dwarf novae, making this the first confirmed superoutburst of the star.
Title: Survey of Period Variations of Superhumps in SU UMa-Type Dwarf Novae
CATACLYSMIC VARIABLE STARS--novae, dwarf novae, and their relatives--are among the most fascinating variables that backyard observers follow.
The outburst was detected by JS (4) on 2011 Jan 27 at mag 15.6 during the course of a search for infrequently outbursting dwarf novae. The overall lightcurve of the outburst is shown in Figure 1 a and expanded views of the longer photometry runs in Figure 2, where each panel shows one day of data drawn to the same scale.
Title: Photometric Studies of New Southern SUUMa-Type Dwarf Novae, FL Trianguli Australis and CTCV J0549-4921