The Carbon Mira Uv Aurigae and Its Companion

Abstract

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 3. 36, 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.

High-resolution spectroscopy of two carbon stars with long-term obscuration events

“…Herbig () has detected high‐velocity Na i D components in the spectrum of the binary companion of carbon Mira UV Aur, which suggests that they originate from the shells ejected by the carbon star at a velocity of at least 116 km s −1 . As Herbig notes, this velocity considerably exceeds the typical outflow velocity for carbon stars.…”