The 2001 Superoutburst of WZ Sagittae

Patterson, Joseph; Masi, G.; Richmond, M.; Martin, Brian; Beshore, E. C.; Skillman, David R.; Kemp, Jonathan; Vanmunster, Tonny; Rea, Robert; Allen, William H.; Davis, Stacey M.; Davis, Tracy C.; Henden, A. A.; Starkey, Donn R.; Foote, Jerry; Oksanen, A.; Cook, Lewis M.; Fried, Robert; Husar, D.; Novák, Rudolf; Campbell, Tut; Robertson, J. W.; Krajci, Thomas; Павленко, Е. П.; Mirabal, N.; Niarchos, P. G.; Brettman, O. H.; Walker, Stan

doi:10.1086/341696

Cited by 137 publications

(156 citation statements)

References 62 publications

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“…This can quenchṀ 2 , because starspots are characterized by lower H than the surrounding photospheric regions (Livio & Pringle 1994;King & Cannizzo 1998; but also see Howell et al 2000). 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.…”

Section: Physical Causes Of Long-termṁ 2 Fluctuationsmentioning

confidence: 96%

The Evolution of Cataclysmic Variables as Revealed by Their Donor Stars

Knigge

Baraffe

Patterson

2011

ApJS

Self Cite

585

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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Section: Physical Causes Of Long-termṁ 2 Fluctuationsmentioning

confidence: 96%

The Evolution of Cataclysmic Variables as Revealed by Their Donor Stars

Knigge

Baraffe

Patterson

2011

ApJS

Self Cite

585

879

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“…Reflares (also known in the literature as "rebrightenings," "echo-outbursts," "mini-outbursts" and "flaring-tail") have been observed in a number of different systems, including dwarf novae (WZ Sge, Patterson et al 2002;EG Cnc, Osaki et al 2001; ER UMA Robertson et al 1995;Patterson et al 2013, AL Com Howell et al 1996, UZ Boo, Kuulkers et al 1996; BK Lyn Patterson et al 2013), neutron stars (e.g., KS 1731-260, Šimon 2010, SAX J1750.8-2900 Allen et al 2015 and possibly IGR J00291+5934, Lewis et al 2010) and black hole low-mass X-ray binaries (LMXBs) (e.g., XTE J1650-500, Tomsick et al 2004; GRO J0422+32, Kuulkers et al 1996;GRS 1009-45, Bailyn & Orosz 1995XTE J1859+226, Zurita et al 20024U 15434U -47, Li et al 1976. The ubiquity of the phenomenon among different types of accreting compact objects suggests that reflares are related to specific properties of the accretion disk itself rather than properties of the compact object.…”

Section: Introductionmentioning

confidence: 99%

The Reflares and Outburst Evolution in the Accreting Millisecond Pulsar Sax J1808.4–3658: A Disk Truncated Near Co-Rotation?

Patruno

Maitra

Curran

et al. 2016

ApJ

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The accreting millisecond X-ray pulsar SAX J1808.4-3658 shows peculiar low luminosity states known as "reflares" after the end of the main outburst. During this phase the X-ray luminosity of the source varies by up to three orders of magnitude in less than 1-2 days. The lowest X-ray luminosity observed reaches a value of 10 erg s 32 1 -, only a factor of a few brighter than its typical quiescent level. We investigate the 2008 and 2005 reflaring state of SAX J1808.4-3658 to determine whether there is any evidence for a change in the accretion flow with respect to the main outburst. We perform a multiwavelength photometric and spectral study of the 2005 and 2008 reflares with data collected during an observational campaign covering the near-infrared, optical, ultra-violet and X-ray band. We find that the NIR/optical/UV emission, expected to come from the outer accretion disk, shows variations in luminosity over an order of magnitude. The corresponding X-ray luminosity variations are instead much deeper, spanning about 2-3 orders of magnitude. The X-ray spectral state observed during the reflares does not change substantially with X-ray luminosity, indicating a rather stable configuration of the accretion flow. We investigate the most likely configuration of the innermost regions of the accretion flow and we infer an accretion disk truncated at or near the co-rotation radius. We interpret these findings as due to either a strong outflow (due to a propeller effect) or a trapped disk (with limited/no outflow) in the inner regions of the accretion flow.

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“…Patterson et al (2002) recently presented extensive photometry observations of the 2001 superoutburst of WZ Sge.…”

Section: Introductionmentioning

confidence: 99%

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

Osaki

Meyer

2003

A&A

171

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Abstract. Outburst mechanisms of SU UMa-type dwarf novae are discussed. Two competing models were proposed; a pure disk instability model called the thermal-tidal instability model (TTI model) and the enhanced mass transfer model (EMT model). Observational evidence for enhanced mass transfer from the secondary star during outbursts is critically examined. It is demonstrated that most evidence for enhanced mass transfer is not well substantiated. Patterson et al. (2002) have recently claimed to have found evidence for enhanced mass transfer during the 2001 outburst of WZ Sge. We show that their evidence is probably due to a misinterpretation of their observed light curves. Our theoretical analysis also shows that irradiation during outburst should not affect the mass transfer rate. A refinement of the TTI model is proposed that can explain why superhumps appear a few days after the superoutburst maximum in some SU UMa stars. We present our own interpretation of the overall development of the 2001 outburst of WZ Sge based on the TTI model that does not require the assumption of an unproved enhanced mass transfer.

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The 2001 Superoutburst of WZ Sagittae

Cited by 137 publications

References 62 publications

The Evolution of Cataclysmic Variables as Revealed by Their Donor Stars

The Evolution of Cataclysmic Variables as Revealed by Their Donor Stars

The Reflares and Outburst Evolution in the Accreting Millisecond Pulsar Sax J1808.4–3658: A Disk Truncated Near Co-Rotation?

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

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