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 light curve 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 on the order of 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 light curve 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 Δy ≈ 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, 1.1 M☉, 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 light curve with this formula yields a predicted column within 20% of that estimated from our full numerical calculations.
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机译：我们使用模拟和分析估算，跟踪在矮新星爆发中突然积聚的白矮星（WD）随时间的热演化。当WD通量较高时，爆发后光曲线清晰地分为早期，当WD通量接近静态水平时则为后期。这两个状态之间的中断（一次以爆发持续时间的顺序发生）对应于热扩散波到达新堆积层的底部。我们的主要结果是，在爆发后很长时间，关于静态通量的分数通量扰动随着时间（而不是指数）随幂律而衰减。我们使用这个结果来构建一个简单的拟合公式，该公式可以得出静态通量和吸积柱的估计值，即总吸积质量除以WD表面积。 WD的质量本身并不能很好地受后期光曲线的限制，但是如果从观察中知道吸积的质量，则可以推断出WD的质量。我们将我们的工作与WZ Sge的研究充分的爆发进行了比较，发现我们的模型很好地描述了冷却过程，给出了有效温度Teff = 14,500 K并产生了Δy≈106 g cm-2的柱，与Godon等。为了使该吸积柱与通过辐射热吸收光度推断出的吸积质量相一致，需要大的WD质量，即1.1M☉。我们的幂定律结果是快速评估突出特性的宝贵工具。我们表明，使用此公式拟合后期光曲线会产生一个预测的列，该列在根据我们的完整数值计算得出的估计值的20％以内。
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