Is evidence for enhanced mass transfer during dwarf-nova outbursts well substantiated?

Osaki, Yoji; Meyer, F.

doi:10.1051/0004-6361:20030115

Cited by 96 publications

(187 citation statements)

References 48 publications

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“…systems are characterized by small and positive period derivatives. This picture has a physical interpretation proposed by Osaki & Meyer (2003). In long-period dwarf-novae with high transfer rates, the 3:1 resonance radius in the accretion disc is close to the tidal truncation radius, and eccentric waves in the disc may thus propagate only inwards, proding a decrease in the superhump period.…”

Section: Discussionsupporting

confidence: 63%

CURious Variables Experiment (CURVE): CCD photometry of active dwarf nova DI Ursae Majoris

Rutkowski

Olech

Wiśniewski

et al. 2009

A&A

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Context.We report an analysis of photometric behaviour of DI UMa, an extremely active dwarf nova. The observational campaign (completed in 2007) covers five superoutbursts and four normal outbursts. Aims. We examined principal parameters of the system to understand peculiarities of DI UMa, and other active cataclysmic variables. Methods. Based on precise photometric measurements, temporal light curve behaviour, O−C analysis, and power spectrum analysis, we investigated physical parameters of the system. Results. We found that the period of the supercycle now equals 31.45 ± 0.3 days. Observations during superoutbursts infer that the period of superhumps equals P sh = 0.055318(11) days (79.66 ± 0.02 min). During quiescence, the light curve reveals a modulation of period P orb = 0.054579(6) days (78.59 ± 0.01 min), which we interpret as the orbital period of the binary system. The values obtained allowed us to determine a fractional period excess of 1.35% ± 0.02%, which is surprisingly small compared to the usual value for dwarf novae (2%-5%). A detailed O−C analysis was performed for two superoutbursts with the most comprehensive coverage. In both cases, we detected an increase in the superhump period with a mean rate ofṖ/P sh = 4.4(1.0) × 10 −5 . Conclusions. Based on these measurements, we confirm that DI UMa is probably a period bouncer, an old system that reached its period minimum a long time ago, has a secondary that became a degenerate brown dwarf, the entire system evolving now toward longer periods. DI UMa is an extremely interesting object because we know only one more active ER UMa star with similar characteristics (IX Dra).

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Section: Discussionsupporting

confidence: 63%

CURious Variables Experiment (CURVE): CCD photometry of active dwarf nova DI Ursae Majoris

Rutkowski

Olech

Wiśniewski

et al. 2009

A&A

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“…Similarly, there is some observational evidence that the mass-transfer rate from the secondary may be enhanced during DN eruptions (Patterson et al 2002;Steeghs 2004;Smak 2004a). This may be due to irradiation-driven heating of the upper atmospheric layers in the donor star, causing an increase in H and henceṀ 2 (Smak 2004b(Smak , 2004c; but also see Osaki & Meyer 2003. However, neither of these types of variations occur on the long timescales relevant to us here.…”

Section: Physical Causes Of Long-termṁ 2 Fluctuationsmentioning

confidence: 69%

The Evolution of Cataclysmic Variables as Revealed by Their Donor Stars

Knigge

Baraffe

Patterson

2011

ApJS

568

879

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We present an attempt to reconstruct the complete evolutionary path followed by cataclysmic variables (CVs), based on the observed mass-radius relationship of their donor stars. Along the way, we update the semi-empirical CV donor sequence presented previously by one of us, present a comprehensive review of the connection between CV evolution and the secondary stars in these systems, and reexamine most of the commonly used magnetic braking (MB) recipes, finding that even conceptually similar ones can differ greatly in both magnitude and functional form. The great advantage of using donor radii to infer mass-transfer and angular-momentum-loss (AML) rates is that they sample the longest accessible timescales and are most likely to represent the true secular (evolutionary average) rates. We show explicitly that if CVs exhibit long-term mass-transfer-rate fluctuations, as is often assumed, the expected variability timescales are so long that other tracers of the mass-transfer rate-including white dwarf (WD) temperatures-become unreliable. We carefully explore how much of the radius difference between CV donors and models of isolated main-sequence stars may be due to mechanisms other than mass loss. The tidal and rotational deformation of Roche-lobe-filling stars produces 4.5% radius inflation below the period gap and 7.9% above. A comparison of stellar models to mass-radius data for non-interacting stars suggests a real offset of 1.5% for fully convective stars (i.e., donors below the gap) and 4.9% for partially radiative ones (donors above the gap). We also show that donor bloating due to irradiation is probably smaller than, and at most comparable to, these effects. After calibrating our models to account for these issues, we fit self-consistent evolution sequences to our compilation of donor masses and radii. In the standard model of CV evolution, AMLs below the period gap are assumed to be driven solely by gravitational radiation (GR), while AMLs above the gap are usually described by an MB law first suggested by Rappaport et al. We adopt simple scaled versions of these AML recipes and find that these are able to match the data quite well. The optimal scaling factors turn out to be f GR = 2.47 ± 0.22 below the gap and f MB = 0.66 ± 0.05 above (the errors here are purely statistical, and the standard model corresponds to f GR = f MB = 1). This revised model describes the mass-radius data significantly better than the standard model. Some of the most important implications and applications of our results are as follows. (1) The revised evolution sequence yields correct locations for the minimum period and the upper edge of the period gap; the standard sequence does not. (2) The observed spectral types of CV donors are compatible with both standard and revised models. (3) A direct comparison of predicted and observed WD temperatures suggests an even higher value for f GR , but this comparison is sensitive to the assumed mean WD mass and the possible existence of mass-transfer-rate fluctuations. (4) The pred...

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“…Such a revision of the model has been proposed recently by Osaki & Meyer (2003). We use t l = 1.75 d which accounts for the observed delay between the optical rise and the appearance of Superhumps (see Sect.…”

Section: The Timescale Of the Tidal Instabilitymentioning

confidence: 99%

“…In addition, the claimed observational evidence for enhanced mass transfer during outburst (Vogt 1983;Smak 1991Smak , 1995Patterson et al 2002) has recently been questioned by Osaki & Meyer (2003). Additional information which may help us to constrain the models comes from simultaneous multi-wavelength observations.…”

Section: Introductionmentioning

confidence: 99%

Delays in dwarf novae II: VW Hyi, the tidal instability and enhanced mass transfer models

Schreiber

Hameury

Lasota³

2004

A&A

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Abstract.We discuss the multi-wavelength predictions of the two models proposed for SU UMa stars, i.e. the enhanced mass transfer (EMT) and the tidal thermal instability (TTI) models. We focus on the systematic differences of the suggested scenarios before discussing the model predictions together with the observations of the best-studied SU UMa system, VW Hyi. We find that assuming the standard form of the viscosity parameter α, both models predict only outbursts being triggered at the inner edge of the accretion disc. In the TTI model the superoutbursts are triggered when the outer radius of the disc reaches a certain value, i.e. the 3:1 resonance radius. In contrast, the EMT scenario predicts superoutbursts when the disc mass exceeds a critical value. This causes the EMT model to be much more sensitive to mass transfer variations than the TTI model. In both models we find the predicted UV and EUV delays in agreement with the observations of VW Hyi for α h /α c < ∼ 4. In addition both models can generate precursor outbursts which are more pronounced at short wavelengths, in agreement with observations. Variations found in the observed light curve of single systems (e.g. VW Hyi) as well as the difference between ordinary SU UMa stars and ER UMa systems are a natural outcome of the EMT model while the TTI model fails to explain them.

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Is evidence for enhanced mass transfer during dwarf-nova outbursts well substantiated?

Cited by 96 publications

References 48 publications

CURious Variables Experiment (CURVE): CCD photometry of active dwarf nova DI Ursae Majoris

CURious Variables Experiment (CURVE): CCD photometry of active dwarf nova DI Ursae Majoris

The Evolution of Cataclysmic Variables as Revealed by Their Donor Stars

Delays in dwarf novae II: VW Hyi, the tidal instability and enhanced mass transfer models

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