The Cooling White Dwarf in VW Hydri after Normal Outburst and Superoutburst: [ITAL]HST[/ITAL] Evidence of A Sustained Accretion Belt

Sion, E. M.; Cheng, Fuhua; Huang, Min; Hubený, I.; Szkody, Paula

doi:10.1086/310318

Cited by 49 publications

(52 citation statements)

References 10 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…In those systems, the white dwarf is heated during dwarf nova outbursts and subsequently cools exponentially to its quiescence temperature. The postoutburst cooling timescales that have been found range from a few days to a few weeks (comparable to the duration of the outburst itself, e.g., VW Hyi: Gänsicke & Beuermann 1996;Sion et al 1996) to many years (much longer than the duration of the outburst, e.g., WZ Sge: Slevinsky et al 1999;Godon et al 2004;Long et al 2004;AL Com: Szkody et al 2003). From the observations presented here and by Gänsicke et al (1995), we conclude that the cooling of the white dwarf following the transition from a high state to a low state proceeds either on timescales of a few weeks or less (so that it has not been caught by any of the past FUV observations) or on timescales much longer than the duration of a low state (so that no noticeable cooling is observed throughout the low state), or that the bulk of the white dwarf is not heated at all during the high state.…”

Section: Discussionmentioning

confidence: 99%

FUSEandHSTSTIS Far‐Ultraviolet Observations of AM Herculis in an Extended Low State

Gänsicke

Long

Barstow

et al. 2006

ApJ

Self Cite

View full text Add to dashboard Cite

We have obtained FUSE and HST STIS time-resolved spectroscopy of the Polar AM Herculis during a deep low state. The spectra are entirely dominated by the emission of the white dwarf. Both the far-ultraviolet ( FUV ) flux and the spectral shape vary substantially over the orbital period, with maximum flux occurring at the same phase as during the high state. The variations are due to the presence of a hot spot on the white dwarf, which we model quantitatively. The white dwarf parameters can be determined from a spectral fit to the faint-phase data, when the hot spot is self-eclipsed. Adopting the distance of 79 þ8 À6 pc determined by Thorstensen, we find an effective temperature of 19;800 AE 700 K and a mass of M WD ¼ 0:78 þ 0:12 À 0:17 M . The hot spot has a lower temperature than during the high state, $34,000-40,000 K, but covers a similar area, $10% of the white dwarf surface. Low-state FUSE and STIS spectra taken during four different epochs in [2002][2003] show no variation of the FUV flux level or spectral shape, implying that the white dwarf temperature and the hot spot temperature, size, and location do not depend on the amount of time the system has spent in the low state. Possible explanations are ongoing accretion at a low level or deep heating; both alternatives have some weaknesses, which we discuss. No photospheric metal absorption lines are detected in the FUSE and STIS spectra, suggesting that the average metal abundances in the white dwarf atmosphere are lower than $10 À3 times their solar values.

show abstract

Section: Discussionmentioning

confidence: 99%

FUSEandHSTSTIS Far‐Ultraviolet Observations of AM Herculis in an Extended Low State

Gänsicke

Long

Barstow

et al. 2006

ApJ

Self Cite

View full text Add to dashboard Cite

show abstract

“…(1998) for but held the disk inclination and the white dwarḟ m mass fixed as above. Our accretion belt models were constructed in the same manner as described in Sion et al (1996). A detailed discussion of the accretion belt models can also be found in Sion et al (2001).…”

Section: Synthetic Spectral Fittingmentioning

confidence: 99%

A Hubble Space Telescope STIS Observation of VW Hydri at the Exact Far-Ultraviolet Onset of an Outburst

Sion¹,

Cheng²,

Gänsicke³

et al. 2004

ApJ

Self Cite

View full text Add to dashboard Cite

We present an analysis of Hubble Space Telescope (HST) Space Telescope Imaging Spectrograph data of VW Hyi that we acquired 14 days after a superoutburst. At the time of our observation, the system appears to be going into outburst with the longest wavelengths increasing in flux by a factor of 5 while the shortest wavelengths increase by only a factor of 2. Using the distance of 65 pc, a system inclination angle of 60Њ, and a white dwarf mass of 0.86, we carried out model fits involving a white dwarf by itself; an optically thick accretion disk M , by itself; a composite model using an optically thick accretion disk and a white dwarf; a two-temperature white dwarf model with a cooler, more slowly rotating photosphere and a hotter, rapidly rotating accretion belt; and a composite model involving a white dwarf and a rapidly rotating cooler disk ring heated up to a "low" temperature of 13-14,000 K. This component of temperature stays fairly constant throughout the HST observations, while the area of the disk ring increases by a factor of 12. We see evidence of a delay in the UV emission consistent with the outburst beginning outside of a disk truncation radius.

show abstract

“…A variation of temperature with latitude is expected during tangential accretion from a disk, and a rapidly spinning accretion belt is predicted to be present. Sion et al (1996Sion et al ( , 2001) and Gän-sicke & Beuermann (1996) have shown that an accretion belt is present in the case of VW Hydri based on white dwarf plus accretion belt composite fits to the Hubble Space Tele- We carried out trial composite fits to SWP28683 with fixed belt gravity log g ¼ 6 and fixed belt velocity V sin i ¼ 3400 km s À1 , the Keplerian velocity at the white dwarf surface. As an indicator of the plausibility of a twotemperature fit, we selected a distance of 136 pc as the '' best-fitting '' distance for comparison.…”

Section: Observationsmentioning

confidence: 99%

The Extraordinary Cataclysmic Binary RU Pegasi: The Hottest White Dwarf in a Dwarf Nova?

Sion

Urban

2002

ApJ

Self Cite

View full text Add to dashboard Cite

We present the results of the first multicomponent synthetic spectral analysis of International Ultraviolet Explorer (IUE) archival spectra of the long-period dwarf nova RU Peg during quiescence. The best-fit, highgravity, solar composition photosphere models yield T eff ¼ 50; 000 53; 000 K with scale factor distances of 250 pc. Optically thick accretion disk models imply accretion rates between 1 Â 10 À9 and 1 Â 10 À10 M yr À1 in order to match the steeply sloping far-UV continuum. However, the best-fit accretion disk models yield distances from 600 to 1300 pc, well beyond the estimated distance range of 130-300 pc. Using rough theoretical flux arguments and the distance estimates, we find better agreement between the observed far-UV luminosity and the predicted far-UV luminosity of a hot, massive, white dwarf model than with an accretion disk model. RU Peg appears to contain the hottest white dwarf yet found in a dwarf nova. We cannot rule out that the far-UV energy distribution is due to a multitemperature white dwarf with cooler, more slowly rotating higher latitudes and a rapidly spinning, hotter equatorial belt. We discuss implications of our analysis for theoretical predictions of the disk instability theory of dwarf nova outbursts. We discuss a comparison between RU Peg's white dwarf and the observed properties of other analyzed white dwarfs in dwarf novae.

show abstract

The Cooling White Dwarf in VW Hydri after Normal Outburst and Superoutburst: [ITAL]HST[/ITAL] Evidence of A Sustained Accretion Belt

Cited by 49 publications

References 10 publications

FUSEandHSTSTIS Far‐Ultraviolet Observations of AM Herculis in an Extended Low State

FUSEandHSTSTIS Far‐Ultraviolet Observations of AM Herculis in an Extended Low State

A Hubble Space Telescope STIS Observation of VW Hydri at the Exact Far-Ultraviolet Onset of an Outburst

The Extraordinary Cataclysmic Binary RU Pegasi: The Hottest White Dwarf in a Dwarf Nova?

Contact Info

Product

Resources

About