A Universal Decline Law of Classical Novae
A Universal Decline Law of Classical Novae
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DOI：
10.1086/508063
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发表时间：
2006-07
期刊：
影响因子：
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通讯作者：
I. Hachisu;M. Kato
中科院分区：
文献类型：
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作者：
I. Hachisu;M. Kato
我们计算了不同白矮星质量和化学成分的许多不同的新星光曲线，假设来自光学薄的抛射物的自由-自由发射主导着连续谱通量。我们证明了所有这些光曲线都是同源的，并且通过引入“时间标度因子”可以推导出一个普适定律。宇宙定律的模板光曲线的斜率F∝t在中部(低于光学最大值2~6 mag)为F∝t-1.75，但在后期(~6~10 mag)下降幅度更大，F∝t-3.5，其中t是从爆发开始的时间，以天为单位.光曲线上的这一突变是由于风质量损失率的快速下降。新星的演化大致是按爆发时间来衡量的。一旦破裂时间被观测确定，我们就可以得出紫外线爆发阶段的周期，光学厚风阶段的持续时间，以及氢壳燃烧的关闭日期。根据F∝t-1.75的关系式，得到了一个经验观测公式：t3=(1.6 8±0.0 8)t2+(1.9±1.5)天，其中t2和t3分别是新星从光学极大值衰减2和3mag的天数。我们将我们的模板光曲线模型应用于三颗观测较好的新星V1500 Cyg、V1668 Cyg和V1974 Cyg。我们的理论光曲线与光学Y和红外J、H、K光曲线符合得很好。用IUE观测到的连续谱UV 1455？光曲线重现性很好。我们的模型也同时解释了用ROSAT观测到的超软X射线的开启和关闭。根据光曲线拟合，估计V1500 Cyg的随钻质量为MWD≈1.15M☉，V1668 Cyg的随钻质量为0.95M≈，V1974 Cyg的随钻质量为0.95-1.05M☉，以及喷射物的适当化学成分。
We calculate many different nova light curves for a variety of white dwarf masses and chemical compositions, with the assumption that free-free emission from optically thin ejecta dominates the continuum flux. We show that all these light curves are homologous and a universal law can be derived by introducing a "time scaling factor." The template light curve for the universal law has a slope of flux F ∝ t-1.75 in the middle part (from ~2 to ~6 mag below the optical maximum), but it declines more steeply, F ∝ t-3.5, in the later part (from ~6 to ~10 mag), where t is the time from the outburst in units of days. This break on the light curve is due to a quick decrease in the wind mass-loss rate. The nova evolutions are approximately scaled by the time of break. Once the time of break is observationally determined, we can derive the period of a UV burst phase, the duration of optically thick wind phase, and the turnoff date of hydrogen shell-burning. An empirical observational formula, t3 = (1.68 ± 0.08) t2 + (1.9 ± 1.5) days, is derived from the relation of F ∝ t-1.75, where t2 and t3 are the times in days during which a nova decays by 2 and 3 mag from the optical maximum, respectively. We have applied our template light curve model to the three well-observed novae, V1500 Cyg, V1668 Cyg, and V1974 Cyg. Our theoretical light curves show excellent agreement with the optical y and infrared J, H, K light curves. The continuum UV 1455 Å light curves observed with IUE are well reproduced. The turn-on and turn-off of supersoft X-ray observed with ROSAT are also explained simultaneously by our model. The WD mass is estimated, from the light curve fitting, to be MWD ≈ 1.15 M☉ for V1500 Cyg, MWD ≈ 0.95 M☉ for V1668 Cyg, and MWD ≈ 0.95-1.05 M☉ for V1974 Cyg, together with the appropriate chemical compositions of the ejecta.