Hst/stis Spectroscopy and Modeling of the Long Term Cooling of Wz Sagittae following the July 2001 Outburst
Hst/stis Spectroscopy and Modeling of the Long Term Cooling of Wz Sagittae following the July 2001 Outburst
复制标题
2001 年 7 月爆发后 Wz Sagittae 长期冷却的 Hst/stis 光谱和建模
DOI：
--
复制
发表时间：
2006
期刊：
影响因子：
--
通讯作者：
P. Szkody
中科院分区：
文献类型：
--
作者：
P. Godon;E. Sion;F. Cheng;K. Long;B. Gänsicke;P. Szkody
我们提出了最新的哈勃太空望远镜（HST）空间望远镜成像光谱仪（STIS）E140 M光谱的矮新星WZ Sge，在2004年7月获得的，3年后的早期超爆发的2001年7月。该远紫外（FUV）光谱覆盖了1150- 1725 nm的波长范围，揭示了斯塔克加宽的Lyα吸收和来自一系列电离态的金属吸收线。Lyα和CIV双峰发射仍然存在，表明存在光学薄盘。单颗白色矮星的合成光谱拟合（使用log g = 8.5）与数据表明，白色矮星现在已经达到温度T ≈ 15，000 ± 500 K。爆发后3年，WD仍比其静止温度高1500 K左右，其FUV通量水平几乎是爆发前的两倍，其-2-能谱在1400 K附近没有明显地表现出IUE和HST/GHRS爆发前数据中的准分子氢特征。这清楚地表明，即使在爆发三年后，该系统仍然显示出爆发的影响。考虑到以前的温度估计在冷却的早期阶段，我们的模型WZ Sge的冷却曲线，在一段时间内的三年，使用恒星演化代码，包括吸积和压缩加热的影响。假设压缩加热是冷却阶段释放能量的唯一来源，我们发现：（1）白色的质量一定很大（1.0 ± 0.2 M）;（2）质量吸积率的时间平均值（超过52天的爆发）必须达到10 −8 M yr −1或更高。从这些压缩加热模型得出的爆发质量吸积速率比从光学观测（Patterson等人，2002年）和FUV光谱拟合（Long等人，2003年）估计的速率大一个数量级。这意味着在冷却阶段，WD释放的能量不仅仅是由于压缩加热。我们认为，在静止期以适度低的吸积率进行的吸积也可以以边界层辐射的形式释放大量的能量，这可以使星星的温度升高数千度。激变变星-恒星：个体（WZ Sge）-白色矮星。
We present the latest Hubble Space Telescope (HST) Space Telescope Imaging Spectrograph (STIS) E140M spectrum of the dwarf nova WZ Sge, obtained in July 2004, 3 years following the early superoutburst of July 2001. This far-ultraviolet (FUV) spectrum covers the wavelength interval 1150-1725Å, revealing Stark-broadened Lyα absorption and absorption lines due to metals from a range of ionization states. The Lyα and CIV double peak emissions are still present, indicating the presence of an optically thin disk. Single white dwarf synthetic spectral fits (using log g = 8.5) to the data indicate that the white dwarf has now reached a temperature T ≈ 15, 000 ± 500K. Three years after the outburst the WD is still ∼1500K above its quiescent temperature, it has an FUV flux level almost twice its pre-outburst value, and its – 2 – spectrum does not distinctly exhibit the quasi-molecular hydrogen feature around 1400Å which was present in the IUE and HST/GHRS pre-outburst data. This is a clear indication that even three years after outburst the system is still showing the effect of the outburst. Taking into account previous temperature estimates obtained during the earlier phase of the cooling, we model the cooling curve of WZ Sge, over a period of three years, using a stellar evolution code including accretion and the effects of compressional heating. Assuming that compressional heating alone is the source of the energy released during the cooling phase, we find that (1) the mass of the white dwarf must be quite large (≈ 1.0 ± 0.2M ⊙); and (2) the mass accretion rate must have a time-averaged (over 52 days of outburst) value of the order of 10 −8 M ⊙ yr −1 or above. The outburst mass accretion rate derived from these compressional heating models is larger than the rates estimated from optical observations (Patterson et al. 2002) and from a FUV spectral fit (Long et al. 2003) by up to one order of magnitude. This implies that during the cooling phase the energy released by the WD is not due to compressional heating alone. We suggest that ongoing accretion during quiescence at a moderately low accretion rate can also release a significant amount of energy in the form of boundary layer irradiation, which can increase the temperature of the star by several thousand degrees. Subject headings: Cataclysmic variables – stars: individual (WZ Sge) – white dwarfs.