White Dwarf Heating and Subsequent Cooling in Dwarf Nova Outbursts

نویسنده

  • ANTHONY L. PIRO
چکیده

We follow the time dependent thermal evolution of a white dwarf (WD) undergoing sudden accretion in a dwarf nova outburst, using both simulations and analytic estimates. The post-outburst lightcurve clearly separates into early times when the WD flux is high, and late times when the flux is near the quiescent level. The break between these two regimes, occurring at a time of order the outburst duration, corresponds to a thermal diffusion wave reaching the base of the freshly accreted layer. Our principal result is that long after the outburst, the fractional flux perturbation about the quiescent flux decays as a power law with time (and not as an exponential). We use this result to construct a simple fitting formula that yields estimates for both the quiescent flux and the accreted column, i.e. the total accreted mass divided by WD surface area. The WD mass is not well constrained by the late time lightcurve alone, but it can be inferred if the accreted mass is known from observations. We compare our work with the well-studied outburst of WZ Sge, finding that the cooling is well described by our model, giving an effective temperature Teff = 14,500 K and accreted column ∆y ≈ 106 g cm−2, in agreement with the modeling of Godon et al. To reconcile this accreted column with the accreted mass inferred from the bolometric accretion luminosity, a large WD mass & 1.1M⊙ is needed. Our power law result is a valuable tool for making quick estimates of the outburst properties. We show that fitting the late time lightcurve with this formula yields a predicted column within 20% of that estimated from our full numerical calculations. Subject headings: accretion, accretion disks — novae, cataclysmic variables — stars: individual (WZ Sagittae) — white dwarfs

برای دانلود متن کامل این مقاله و بیش از 32 میلیون مقاله دیگر ابتدا ثبت نام کنید

ثبت نام

اگر عضو سایت هستید لطفا وارد حساب کاربری خود شوید

منابع مشابه

On the occurrence of dwarf nova outbursts in post novae

We show that irradiation of the accretion disc by the white dwarf limits the occurrence of dwarf nova outbursts in post nova accretion discs. After the nova explosion, the white dwarf has to cool for up to ∼ 100 yr – depending on the orbital period (i.e., disc size) and the temperature of the white dwarf after the nova-eruption – before the disc can begin producing dwarf nova outbursts. During ...

متن کامل

The Nature of Dwarf Nova Outbursts

We show that if the dwarf-nova disc instability model includes the effects of heating by stream impact and tidal torque dissipation in the outer disc, the calculated properties of dwarf-nova outbursts change considerably, and several notorious deficiencies of this model are repaired. In particular: (1) outside-in outbursts occur for mass transfer rates lower than in the standard model as requir...

متن کامل

Synthetic NLTE accretion disc spectra for the dwarf nova SS Cyg during an outburst cycle

Context. Dwarf nova outbursts result from enhanced mass transport through the accretion disc of a cataclysmic variable system. Aims. We assess the question of whether these outbursts are caused by an enhanced mass transfer from the late-type main sequence star onto the white dwarf (so-called mass transfer instability model, MTI) or by a thermal instability in the accretion disc (disc instabilit...

متن کامل

Recurrent Novae , Classical Novae , Symbiotic Novae , and Population II

Light curve analysis of decay phase of nova outburst are summarized. Nova duration is determined by the strong wind mass-loss which depends only on the white dwarf mass. Fast novae correspond very massive white dwarfs and very slow novae correspond almost lower mass limit of white dwarfs. This relation is shown in both of classical novae and recurrent novae. Light curves are theoretically repro...

متن کامل

The standstill luminosity in Z Cam systems

We consider accretion discs in close binary systems. We show that heating of a disc at the impact point of the accretion stream contributes significantly to the local energy budget at its outer edge. As a result the thermal balance relation between local accretion rate and surface density (the ‘S–curve’) changes; the critical mass transfer rate above which no dwarf nova outbursts occur can be u...

متن کامل

ذخیره در منابع من


  با ذخیره ی این منبع در منابع من، دسترسی به آن را برای استفاده های بعدی آسان تر کنید

برای دانلود متن کامل این مقاله و بیش از 32 میلیون مقاله دیگر ابتدا ثبت نام کنید

ثبت نام

اگر عضو سایت هستید لطفا وارد حساب کاربری خود شوید

عنوان ژورنال:

دوره   شماره 

صفحات  -

تاریخ انتشار 2005