Dwarf nova outbursts in intermediate polars

Hameury, J. M.; Lasota, Jean–Pierre

doi:10.1051/0004-6361/201730760

Cited by 46 publications

(39 citation statements)

References 50 publications

(57 reference statements)

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“…We thus caution that the presence of a magnetic field B > ∼ 10 5 G may lead us to underestimate the true mass transfer rate in DQ Her systems, and in particular in BG CMi where B ≈ 4 to 10 × 10 6 G (Chanmugam et al 1990). Finally, we note that TV Col, another DQ Her system, shows infrequent and short outbursts but according to Hameury & Lasota (2017) these cannot be attributed to the disk's thermal-viscous instability.…”

Section: Nova-likesmentioning

confidence: 74%

Testing the disk instability model of cataclysmic variables

Dubus

Otulakowska-Hypka

Lasota

2018

A&A

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Context. The disk instability model attributes the outbursts of dwarf novae to a thermal-viscous instability of their accretion disk, an instability to which nova-like stars are not subject. Aims. We aim to test the fundamental prediction of the disk instability model: the separation of cataclysmic variables (CVs) into nova-likes and dwarf novae depending on orbital period and mass transfer rate from the companion. Methods. We analyse the lightcurves from a sample of ≈ 130 CVs with a parallax distance in the Gaia DR2 catalogue to derive their average mass transfer rate. The method for converting optical magnitude to mass accretion rate is validated against theoretical lightcurves of dwarf novae. Results. Dwarf novae (resp. nova-likes) are consistently placed in the unstable (resp. stable) region of the orbital period -mass transfer rate plane predicted by the disk instability model. None of the analysed systems present a challenge to the model. These results are robust against the possible sources of error and bias that we investigated. Lightcurves from Kepler or, in the future, the LSST or Plato surveys, could alleviate a major source of uncertainty, the irregular sampling rate of the lightcurves, assuming good constraints can be set on the orbital parameters of the CVs that they happen to target. Conclusions. The disk instability model remains the solid base on which to construct the understanding of accretion processes in cataclysmic variables.

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Section: Nova-likesmentioning

confidence: 74%

Testing the disk instability model of cataclysmic variables

Dubus

Otulakowska-Hypka

Lasota

2018

A&A

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“…Alternatively, or perhaps additionally, the low outburst frequency may be the result of disruption of the inner disc by the magnetic white dwarf, as suggested by Angelini & Verbunt (1989). Hameury & Lasota (2017) show that dwarf nova outbursts from intermediate polars are expected to be less frequent and of shorter duration than those from non-magnetic CVs. It appears then that V1460 Her could be a marginal candidate for this group, with outbursts every 10 years, lasting about 15 days.…”

Section: Discussionmentioning

confidence: 95%

V1460 Her: a fast spinning white dwarf accreting from an evolved donor star

Ashley

Marsh

Breedt

et al. 2020

Monthly Notices of the Royal Astronomical Society

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We present time-resolved optical and ultraviolet spectroscopy and photometry of V1460 Her, an eclipsing cataclysmic variable with a 4.99 h orbital period and an overluminous K5-type donor star. The optical spectra show emission lines from an accretion disc along with absorption lines from the donor. We use these to measure radial velocities, which, together with constraints upon the orbital inclination from photometry, imply masses of M1 = 0.869 ± 0.006 M⊙ and M2 = 0.295 ± 0.004 M⊙ for the white dwarf and the donor. The radius of the donor, R2 = 0.43 ± 0.002 R⊙, is ≈50 per cent larger than expected given its mass, while its spectral type is much earlier than the M3.5 type that would be expected from a main sequence star with a similar mass. HST spectra show strong N v 1240 Å emission but no C iv 1550 Å emission, evidence for CNO-processed material. The donor is therefore a bloated, over-luminous remnant of a thermal-timescale stage of high mass transfer and has yet to re-establish thermal equilibrium. Remarkably, the HST ultraviolet data also show a strong 30 per cent peak-to-peak, 38.9 s pulsation that we explain as being due to the spin of the white dwarf, potentially putting V1460 Her in a similar category to the propeller system AE Aqr in terms of its spin frequency and evolutionary path. AE Aqr also features a post-thermal timescale mass donor, and V1460 Her may therefore be its weak magnetic field analogue since the accretion disc is still present, with the white dwarf spin-up a result of a recent high accretion rate.

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“…For example, variations of the mass transfer rate are required to explain the Z Cam systems that alternate between bright, steady periods and periods during which they undergo DN outbursts. Truncation of the inner disc by a magnetic field is needed to model the DN phenomenon in intermediate polars (Hameury & Lasota 2017), but truncation (not necessarily magnetic) is also needed to explain outbursts in other sources. Examples of these sources are SS Cyg (Schreiber et al 2003) and WZ Sge stars, which we discuss further in this section, or soft X-ray transients (SXTs), which are low-mass X-ray binary analogues of DNe.…”

Section: Introductionmentioning

confidence: 99%

Modelling rebrightenings, reflares, and echoes in dwarf nova outbursts

Hameury

Lasota

2021

A&A

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Context. The disc instability model (DIM) accounts well for most of the observed properties of dwarf novae and soft X-ray transients, but the rebrightenings, reflares, and echoes occurring at the end of outbursts or shortly after in WZ Sge stars or soft X-ray transients have not yet been convincingly explained by any model. Aims. We determine the additional ingredients that must be added to the DIM to account for the observed rebrightenings. Methods. We analyse in detail a recently discovered system, TCP J21040470+4631129, which has shown very peculiar rebrightenings. We also model the light curve of this system using our numerical code, including mass transfer variations from the secondary, inner–disc truncation, disc irradiation by a hot white dwarf and, in some cases, the mass-transfer stream over(under) flow. Results. We show that the luminosity in quiescence is dominated by a hot white dwarf that cools down on timescales of months. For a reason that remains elusive, the mass transfer rate from the secondary has to increase by several orders of magnitudes during the initial superoutburst. The mass transfer rate slowly returns to its secular average and causes the observed succession of outbursts with increasing quiescence durations until the disc can be steady, cold, and neutral; its inner parts are truncated either by the white dwarf magnetic field or by evaporation. The very short, quiescence phases between reflares are reproduced when the mass-transfer stream overflows the disc. Using similar additions to the DIM, we also produced light curves close to those observed in two WZ Sge stars, the prototype and EG Cnc. Conclusions. Our model successfully explains the reflares observed in WZ Sge systems. It requires, however, the inner disc truncation in dwarf novae to be due not only to the white dwarf magnetic field but, as in X-ray binaries, rather to evaporation of the inner disc. A similar model could also explain reflares observed in soft X-ray transients.

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Dwarf nova outbursts in intermediate polars

Cited by 46 publications

References 50 publications

Testing the disk instability model of cataclysmic variables

Testing the disk instability model of cataclysmic variables

V1460 Her: a fast spinning white dwarf accreting from an evolved donor star

Modelling rebrightenings, reflares, and echoes in dwarf nova outbursts

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