Diffuse interstellar clouds associated with dark clouds

Measurements of CH emission at 9 cm toward the bright stars α Cam and kappa Cas and from dark clouds near the stars reveal an association between diffuse clouds and dark clouds. Here the term diffuse clouds refers to clouds seen in optical absorption; the term dark clouds refers to opaque regions on the Palomar Sky Survey observed through radio techniques. The radio emission toward α Cam, and possible emission twoard kappa Cas, occurs at the same velocity as the optical CH absorption. The column densities derived from both techniques are similar. A dark cloud near each star also shows emission at the velocity of absorption The column density of CH is larger in the dark cloud. From these data, it is concluded that for most lines of sight, diffuse clouds are the outer, relatively transparent portions of dark clouds