... objects

Based on data collected at the 2 m telescope operated on IC AMER Observatory (Terskol, Russia).

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... DIBs

If a spectrum shows DIBs at all, then sodium D lines are always present and strong.

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...$\sigma$

Kreowski & Walker (1987) proposed the division of diffuse clouds in two types based on the intensity ratio of the strong diffuse bands at 5780 and 5797 Å. The $\sigma$-type clouds (after the prototype star $\sigma$ Sco) is characterized by low intensity of interstellar molecules and "narrow" DIBs like 5797 Å. The $\zeta$ type clouds (after the prototype star $\zeta$Oph) show strong molecular lines and deep diffuse bands like 5797 Å.

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