双简并（DA + DQ）NLTT 16249的1.17天轨道
The 1.17-day orbit of the double-degenerate (DA+DQ) NLTT 16249
摘要：
新的光谱观测表明，双简并系统NLTT 16249处于一个周期为1.17 d的闭合轨道（a = 5.6+/-0.3 R_sun）.该系统的总质量估计在1.47到2.04 M_sun之间，但预计不会在哈勃时间尺度内合并（t_merge ~ 10^11 yr）。Vennes & Kawka（2012，ApJ，745，L12）最初是因为特殊的复合氢（DA类）和分子（C_2-DQ类-和CN）光谱而确定该系统的，并且新的观察将该系统确定为第一个DA加DQ紧密双简并系统。此外，DQ组件是同类中第一个显示氮从其大气中的核心中被挖掘出来的组件。这颗恒星可能被视为重生的PG 1159恒星的第一个已知的DQ后裔。或者，氮的存在可能是过去的相互作用和截断的结果在一个紧密的二元系统的演变。
英文摘要：
New spectroscopic observations show that the double degenerate system NLTT 16249 is in a close orbit (a = 5.6+/-0.3 R_sun) with a period of 1.17 d. The total mass of the system is estimated between 1.47 and 2.04 M_sun but it is not expected to merge within a Hubble time-scale (t_merge ~ 10^11 yr). Vennes & Kawka (2012, ApJ, 745, L12) originally identified the system because of the peculiar composite hydrogen (DA class) and molecular (C_2--DQ class--and CN) spectra and the new observations establish this system as the first DA plus DQ close double degenerate. Also, the DQ component was the first of its class to show nitrogen dredged-up from the core in its atmosphere. The star may be viewed as the first known DQ descendant of the born-again PG1159 stars. Alternatively, the presence of nitrogen may be the result of past interactions and truncated evolution in a close binary system.
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