White Dwarfs in Ultrashort Binary Systems

Israel, G. L.; Dall’Osso, S.

doi:10.1007/978-1-4020-9264-0_8

Cited by 2 publications

(3 citation statements)

References 47 publications

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“…By means of these new X-ray datasets, we were able to refine our previous coherent timing solution (Israel et al 2004(Israel et al , 2005Israel & Dall'Osso 2009). According to our analysis, the phase-coherent best inferred X-ray period and period derivative are P = 321.5303822(13) s andṖ = −3.6718(13) × 10 −11 s s −1 ; MJD = 52619.0000 (TDB time) was used as reference epoch for the period derivative.…”

Section: Timing Analysismentioning

confidence: 69%

“…This model, analogous to that proposed for the JupiterIo system, is known as the "unipolar inductor" (UI) or "electric star" model (Wu et al 2002;Wu 2009;Dall'Osso et al 2006Israel & Dall'Osso 2009). Recently, Lai (2012) highlighted a critical inefficiency of this mechanism in dissipating enough energy to match the X-ray emission of the ultracompact A&A 561, A117 (2014) double-WD binaries.…”

Section: Introductionmentioning

confidence: 96%

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SwiftX-ray and ultraviolet observations of the shortest orbital period double-degenerate system RX J0806.3+1527 (HM Cnc)

Esposito

Israel

Dall’Osso

et al. 2014

A&A

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The system RX J0806.3+1527 (HM Cnc) is a pulsating X-ray source with 100 per cent modulation on a period of 321.5 s (5.4 min). This period reflects the orbital motion of a close binary consisting of two interacting white dwarfs. Here we present a series of simultaneous X-ray (0.2-10 keV) and near-ultraviolet (2600 Å and 1928 Å) observations that were carried out with the Swift satellite. In the near-ultraviolet, the counterpart of RX J0806.3+1527 was detected at flux densities consistent with a blackbody with a temperature of (27 ± 8) × 10 3 K. We found that the emission at 2600 Å is modulated at the 321.5-s period with the peak ahead of the X-ray one by 0.28 ± 0.02 cycles and is coincident within ±0.05 cycles with the optical. This phase-shift measurement confirms that the X-ray hot spot (located on the primary white dwarf) is at about 80• -100• from the direction that connects the two white dwarfs. Albeit at lower significance, the 321.5-s signature is also present in the 1928-Å data; at this wavelength, however, the pulse peak is better aligned with that observed at X-rays. We use the constraints on the source luminosity and the geometry of the emitting regions to discuss the merits and limits of the main models for RX J0806.3+1527.

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Section: Timing Analysismentioning

confidence: 69%

Section: Introductionmentioning

confidence: 96%

SwiftX-ray and ultraviolet observations of the shortest orbital period double-degenerate system RX J0806.3+1527 (HM Cnc)

Esposito

Israel

Dall’Osso

et al. 2014

A&A

Self Cite

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“…The discs presented here are geometrically very thin. Overview information about these interesting objects can be found, e.g., in Nelemans (2005) or Israel & Dall'Osso (2009). We chose an AM CVn system in low-state for our study, since the discs in this case are more transparent and colder than in high state, which implies that the velocity field gradient could affect line profiles.…”

Section: Introductionmentioning

confidence: 99%

Influence of the velocity gradient on the line formation in discs of cataclysmic variables

Korčáková

Nagel²,

Werner³

et al. 2011

A&A

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Context. The velocity field gradient in the radiative transfer in disc models of cataclysmic variables (CVs) is usually neglected; however, the geometry of the system and the value of Keplerian velocity suggest that it can be important for high inclination angles. Aims. We investigate the influence of the Keplerian velocity gradient on the line formation in CV discs. Methods. The vertical structure of the disc was determined using the NLTE accretion disc code AcDc, where the hydrostatic equation, the energy balance equation, the radiative transfer equation, the rate equations, and the equations of charge and particle conservation are consistently solved using the accelerated lambda iteration. NLTE opacities and emissivities are interpolated onto a 2D grid, where the radiative transfer equation was then solved with the velocity field taken into account. Results. We show line-profile changes and limb-darkening dependences for the Hα and Hγ lines in a model of SS Cyg, along with the HeI 4923 Å line of a model representing a typical AM CVn system. Both systems are considered in the quiescent phase. Conclusions. The line-profile changes due to the velocity gradient in the disc are small enough for most CV discs to allow the classical approach, where the radiative transfer is solved through the static disc and the velocity field is only taken into account in the final flux integration. However, the exact solution must be performed for CVs, where the disc rim plays an important role (inclination angles almost 90 • ). Extremely cool and relatively transparent discs under high inclinations should also be investigated with detailed radiative transfer models.

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White Dwarfs in Ultrashort Binary Systems

Cited by 2 publications

References 47 publications

SwiftX-ray and ultraviolet observations of the shortest orbital period double-degenerate system RX J0806.3+1527 (HM Cnc)

SwiftX-ray and ultraviolet observations of the shortest orbital period double-degenerate system RX J0806.3+1527 (HM Cnc)

Influence of the velocity gradient on the line formation in discs of cataclysmic variables

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