2015AJ....149..109S

We obtained high-resolution infrared spectroscopy of the long period binary, ε Aurigae, in the vicinity of the near-infrared overtone band of CO, at four epochs during 2011-2012. These observations span the period from late phase of the recent eclipse, to after the eclipse. Lines of both ¹²CO and ¹³CO were observed, confirming the report from the 1983 eclipse that these features were present during the second half of the eclipse. The bands were absent post-eclipse, consistent with their formation only in the several AU diameter disk that has been shown to cause the eclipse. We fitted the eclipse spectra with CO column densities 8x10¹⁹/cm2 at 1275 K when nearer to mid-eclipse, and 1.5x10²⁰/cm2 at 1050 K during third contact. We also found that ¹²C/¹³C = 5±1 in the disk. Assuming that mass transfer from the primary star formed the disk, this implies a helium core burning evolutionary state for the primary star. We also obtained a high-resolution post-eclipse spectrum of the 4.05 µm Brackett α emission line. The small radial velocity difference of the emission, relative to a nearby photospheric line of primary star origin, indicates that the emission may arise from nearer the system center of mass, such as a recombination region larger than the immediate vicinity of the unseen companion star surrounded by the disk. The combination of CO and Brα lines provides important diagnostics for resolving ongoing questions about the evolutionary state of this system.