A New Look at the Dark Cloud L1251: Sensitive Observations of the Molecular Emission

High-sensitivity observations in the (12)CO, (13)CO, C(18)O, H(13)CO(+), and SiO line have been made of the dark cloud L1251 in Cepheus. The (13)CO gas shows a cometary distribution with a U-shaped dense 'head' having a highly ordered velocity gradient in the direction parallel to the minor axis of the cloud. Five C(18)O cores characterized by a mass of approx. 50 Solar mass and a mean density of approximately 3 x 10³ cc are embedded in the (13)CO cloud. Three of them have associated far-infrared sources, suggesting that stars have recently formed there. High angular resolution (12)CO observations have revealed a well-collimated compact outflow confined in the most massive, densest C(18)O core. Its driving source is embedded in a small H(13)CO(+) core with a mass of approximately 1-3 Solar mass. A possibility is suggested that the U shape of the cloud and its well-defined velocity gradient may have resulted from some dynamical interaction with the ambient matter.