EUVE Observations of U Geminorum in Outburst

Long, Knox S.; Mauche, Christopher W.; Raymond, J. C.; Szkody, Paula; Mattei, J. A.

doi:10.1086/177832

Cited by 77 publications

(103 citation statements)

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“…However, similar light-curve features in various wavelength ranges have also been recorded for a number of cataclysmic binaries in outburst, such as U Gem [11,12], OY Car [13,14], and Z Cha [15]. Further observations showed that lightcurve dips can also appear when a system is in a stationary state.…”

Section: Introductionsupporting

confidence: 61%

The possible nature of dips in the light curves of semidetached binaries with stationary disks

et al. 2005

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A thickening at the outer edge of the accretion disk is usually invoked to explain the dips in the light curves of cataclysmic variables with stationary disks at phases ∼ 0.7. The non-collisional interaction between the stream and the disk in the stationary solution raises the question of why matter appears at a considerable height above the accretion disk in such systems. Our three-dimensional numerical modeling demonstrates that a thickening of the halo above the disk can appear even in the absence of a direct collision between the stream and the disk. In the gas-dynamical flow pattern described with the "hotline" model, a considerable fraction of the matter is accelerated in the vertical direction during the flow's interaction with the circumdisk halo. The vertical motion of the gas due to the presence of the z component of the velocity leads to a gradual thickening of the circumdisk halo. The computations reveal the strongest thickening of the halo above the outer edge of the disk at phases ∼ 0.7, in agreement with observations for stationary-disk cataclysmic variables. This supports the hot-line model suggested earlier as a description of the pattern of the matter flows in semi-detached binaries, and presents new possibilities for interpreting the light curves of such systems.

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Section: Introductionsupporting

confidence: 61%

The possible nature of dips in the light curves of semidetached binaries with stationary disks

et al. 2005

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“…During the outburst decline, both the soft and hard X-rays decrease faster than the optical flux (Mason et al 1978;Swank et al 1978;Córdova & Mason 1984; see also Szkody et al 1999). Values derived for L BL /L disk are ∼0.5 during quiescence , which is among the highest for DNe, and ∼1 during outburst (Long et al 1996). So, in quiescence, as at outburst, U Gem comes closest to the standard BL model.…”

Section: Outbursting Dwarf Novae and Other High-ṁ Cvsmentioning

confidence: 82%

“…A study of the ionization states inferred from the P Cygni lines arising in winds from highṀ CVs led to a similar conclusion (Drew & Verbunt 1985;Hoare & Drew 1991). Various explanations for the discrepancy (or absence) of soft X-ray flux during outburst have been put forward: differences in N H to different systems (e.g., Patterson & Raymond 1985b;Long et al 1996); differences in M WD and the WD rotation (see below); absorption in the disk wind (Jensen 1984;Kallman & Jensen 1985); energy loss in the form of a wind (e.g., Silber et al 1994;Ponman et al 1995). Moreover, changes in the BL temperature can shift most of the flux out of the soft X-ray bandpass (e.g., Córdova et al 1980a;Patterson & Raymond 1985b).…”

Section: Outbursting Dwarf Novae and Other High-ṁ Cvsmentioning

confidence: 90%

“…10.2.5). Note that not all of the soft component is optically thick (Mauche et al 1995;Long et al 1996). The soft X-ray fluxes increase by a factor of ∼100 from quiescence to outburst.…”

Section: Outbursting Dwarf Novae and Other High-ṁ Cvsmentioning

confidence: 99%

“…There are several reasons why L BL may be larger in U Gem than in systems like VW Hyi (see Long et al 1996, and references therein). Studies (Pringle 1977;Popham & Narayan 1995) have shown that, whenṀ is held fixed, the BL temperature and L BL increase substantially with WD mass.…”

Section: Outbursting Dwarf Novae and Other High-ṁ Cvsmentioning

confidence: 99%

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X-rays from cataclysmic variables

Kuulkers

Norton

Schwope

et al. 2006

Compact Stellar X-Ray Sources

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IntroductionCataclysmic Variables * (CVs) are a distinct class of interacting binaries, transferring mass from a donor star to a degenerate accretor, a white dwarf (WD). In all observational determinations, and as is required by theory for stable mass transfer, the donor star is of lower mass than the accretor.The majority of CVs have orbital periods, P orb , between 75 min and 8 h (see Ritter & Kolb 2003) and consist of Roche Lobe-filling main sequence donors and WDs. These are WD analogues of the low-mass X-ray binaries (LMXBs; see Chapter 1). In the period range 8 h-3 d the donors must have larger radii than dwarfs in order to fill their Roche Lobes and are therefore evolved subgiants. A few CVs are found with P orb ∼200 d, which require giant donors for them to be Lobe-filling. The absence of evolved CVs with periods ∼3 to ∼200 d is connected with the dynamical instability that results from an initial donor that had a mass larger than about 67% of that of the WD; such binaries will have experienced rapid mass transfer and shortened their periods during a common envelope phase. Beyond P orb ∼200 d, mass-transferring systems also exist. These constitute the symbiotic binaries (SBs) and are in general not Roche Lobe-filling, but instead consist of a WD orbiting in the wind of a supergiant, and are thus analogues of the high-mass X-ray binaries (see Chapter 1).At the short end of the period range a different kind of CV exists, i.e., in which the mass losing donors are themselves WDs; they are entirely deficient in hydrogen. These helium-transferring CVs are known, after the type star, as AM CVn stars and are observed to have P orb from 60 min down to at least as short as 10 min. They have evolved by passage through two common envelope phases, which leaves the cores of both of the component stars exposed.The CVs are divided into subtypes. These were originally based entirely on the behaviour seen in long-term optical light curves, but to this are now added more subtle parameters such as the presence of polarisation. In essence, a CV's gross behaviour is determined by the rate of mass transfer from the donor,Ṁ donor , and * See Hack & La Dous (1993) and Warner (1995) for comprehensive overviews.

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