Disk Instability Model for the AM Canum Venaticorum Stars

Tsugawa, Motohiko; Osaki, Yoji

doi:10.1093/pasj/49.1.75

Cited by 82 publications

(102 citation statements)

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“…This is also the case for the X-ray transients modeled by Lasota et al (1996) and for DQ Her, a well-known magnetic CV (Dimitrienko 1996). AM CVn, where both donor and donee are low-mass, helium white dwarfs, in contrast, has most of its variability coming from changes in disk viscosity rather than from anything the donor does (Tsugawa & Osaki 1997). The alternation between high (outburst) and low (quiescent) accretion rates, when caused by changes in the disk viscosity, has the character of limit cycling.…”

Section: Causes Of the Dwarf Nova (And Related) Outburstsmentioning

confidence: 53%

Astrophysics in 1997

Trimble¹,

McFadden²

1998

PUBL ASTRON SOC PAC

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ABSTRACT. Martian marvels, a gamma-ray burster with a redshift, Galileo converses with Ganymede, a record galactic redshift of 4.92, and much else. Fiscal 1997 was definitely an exciting year for astronomers. We have tried hard to hit all the obvious highlights, but also to report more gradual progress on traditional problems of understanding planets, stars, galaxies, and the universe. Though the year was saddened by the loss of many valued colleagues, we nevertheless indulge in occasional soupçons of frivolity.

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Section: Causes Of the Dwarf Nova (And Related) Outburstsmentioning

confidence: 53%

Astrophysics in 1997

Trimble¹,

McFadden²

1998

PUBL ASTRON SOC PAC

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“…First, some AM CVn stars suffer disk instabilities, and others do not. The theory for this has been developed by Smak (1983) and Tsugawa & Osaki (1997; the dashed lines in the lower frame of Fig. 9 show the results of Tsugawa & Osaki).…”

Section: ϫ5mentioning

confidence: 91%

The Helium‐rich Cataclysmic Variable ES Ceti

Espaillat

Patterson

Warner

et al. 2005

PUBL ASTRON SOC PAC

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ABSTRACT. We report photometry of the helium-rich cataclysmic variable ES Ceti during [2001][2002][2003][2004]. The star is roughly stable at and has a light curve dominated by a single period of 620 s, which remains measurably V ∼ 17.0 constant over the 3 yr baseline. The weight of evidence suggests that this is the true orbital period of the underlying binary, not a "superhump" as initially assumed. We report GALEX ultraviolet magnitudes that establish a very blue flux distribution and therefore a large bolometric correction. Other evidence (the very strong He ii l4686emission and a ROSAT detection in soft X-rays) also indicates a strong EUV source, and comparison to helium atmosphere models suggests a temperature of kK. For a distance of 350 pc, we estimate a luminosity of 130 ‫ע‬ 10 ergs s Ϫ1 , yielding a mass accretion rate of M , yr Ϫ1 onto an assumed 0.7 M , white 34 Ϫ9(0.8-1.7) # 10 (2-4) # 10 dwarf. This appears to be about as expected for white dwarfs orbiting each other in a 10 minute binary, assuming that mass transfer is powered by gravitational radiation losses. We estimate mean accretion rates for other heliumrich cataclysmic variables and find that they also follow the expected relation. There is some evidence Ϫ5M ∼ P o (the lack of superhumps and the small apparent size of the luminous region) that the mass-transfer stream in ES Cet directly strikes the white dwarf, rather than circularizing to form an accretion disk.

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“…This is the disc size found for AM CVn . For unstable systems like V803 Cen and CR Boo, the disc size according to the thermal-tidal-instability model of Tsugawa & Osaki (1997) can oscillate within the three possibilities, the circularization radius (or the Lubow-Shu radius R LS = 0.29a), the critical radius for the tidal instability R cr = 0.46a and the terminal disc radius R d = 0.36a at the end of a superoutburst. This also gives an average disc radius of 15R 1 which we use as a reference radius for the discs of the AM CVn systems.…”

Section: Setting the Model Gridmentioning

confidence: 99%

“…We will also discuss possible errors in our results. Table 3 includes the observed and predicted values for some of the parameters of the AM CVn systems (Warner 1995b;Tsugawa & Osaki 1997;Nelemans et al 2001). …”

Section: Observations Compared With Nlte Pure Helium Modelsmentioning

confidence: 99%

NLTE accretion disc models for the AM Canum Venaticorum systems

Nasser

Solheim

Semionoff

2001

A&A

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Abstract. We present models of the optical spectra of two types of accretion disc atmospheres: a pure helium model and a H-He model, in a low mass ratio, helium transferring, interacting binary white dwarf system. The computations are restricted to stationary discs in LTE and NLTE cases. We also investigate the influence on the spectra of some of the disc parameters such as the mass accretion rate, the angle of inclination, the H/He mass ratio, and the inner and outer radius of the disc. Departures from LTE are also investigated in order to assess the necessity of computing more complicated and more time consuming models. We found that differences in predicted equivalent widths of helium line computed in LTE and NLTE models range between 10 and 40 percent. Finally we compare our disc models with 4 of the AM CVn systems observed with the Nordic Optical Telescope: AM CVn, HP Lib, V803 Cen and CR Boo to determine their parameters as mass transfer rates and inclinations of their discs.

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Disk Instability Model for the AM Canum Venaticorum Stars

Cited by 82 publications

References 0 publications

Astrophysics in 1997

Astrophysics in 1997

The Helium‐rich Cataclysmic Variable ES Ceti

NLTE accretion disc models for the AM Canum Venaticorum systems

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