The Carbon Mira UV Aurigae and its Companion

The carbon Mira UV Aur (photometric period 394 days) and its companion present several interesting spectroscopic issues. The late B-type companion, at a separation of 3farcs36, is seen through at least two shells expanding from the C9-type primary, as evidenced by a series of narrow, displaced absorption features at the D_1,2 lines of Na I. The (projected) expansion velocity of the fastest shell is about 116 km s^-1, much larger than the typical outflow velocity of about 15 km s^-1 seen in C-type giants, but reminiscent of the velocities observed in the envelope of another C-type Mira, V Hya. Emission lines of H, Ca II, and Na I are present in UV Aur A; its Balmer emission lines are heavily mutilated by overlying C-type absorptions (much as is seen in Me-type Miras), so they must be formed at a lower level. UV Aur B offers the opportunity to test a speculation that the carriers of the diffuse interstellar bands (DIBs), believed to be a family of carbon-containing polyatomic molecules, may be formed in cool, carbon-rich stars. Moderately strong DIBs are indeed present in the spectrum of UV Aur B at about the same strength and velocity seen in nearby (in the sky) B-type stars. But the essential question is, are DIBs present in the outflow from UV Aur A, at the velocities of the Na I shell components? The answer is no, at least at the level permitted by the signal-to-noise ratio of these Keck/HIRES spectrograms.