Program: GN-2008B-Q-110

We propose to take the first near infrared spectra of cool white dwarfs with carbon features in their optical spectra (the DQ white dwarfs). We target two normal DQ white dwarfs showing the Swan bands of C2, and two peculiar DQ (DQp) white dwarfs whose Swan-like bands are shifted to the blue and are more symmetric than the DQ bands. The DQ and DQp may be related as the DQ class gives way to the DQp class below Teff~6500K. There is no satisfactory explanation for the differences in their spectra, a problem that has been known for over a decade. Our near infrared spectroscopy will be the first observation of the Ballik-Ramsay bands of C2 in DQ and, possibly, in the DQp. These new bands arise from transitions to a different upper electronic level and will be a strong diagnostic of proposed Swan-shifting mechanisms such as magnetic or pressure effects. We will also search for bands of C2H and other C and C-H compounds that may be present in these high-pressure atmospheres. Finally, we will test our own hypothesis that the DQp bands are a superposition of C2 and C2- bands. Our goal is to obtain long-needed new data that is critical for identifying the cause of the peculiar spectra of the DQp white dwarfs, and for understanding their role in the spectral evolution of cool white dwarfs, the common end-stage of stellar evolution.