2012ApJ...756L...5V

New spectroscopic observations show that the double-degenerate system NLTT 16249 is in a close orbit (a = 5.6±0.3 R_☉) with a period of 1.17 days. The total mass of the system is estimated between 1.47 and 2.04 M_☉ but it is not expected to merge within a Hubble timescale (t_merge~ 10¹¹ yr). Vennes & Kawka originally identified the system because of the peculiar composite hydrogen (DA class) and molecular (C₂-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.