Further study of the stellar cluster embedded in the Ophiuchus dark cloud complex

Abstract

An extension of a 2- map of the Ophiuchus dark cloud carried out by Grasdalen, Strom, and Strom has brought to 67 the total number of detected 2- point sources. Additional infrared photometry has considerably strengthened our previous conclusion that these sources represent the brighter members of a young cluster obscured by dark-cloud material. The luminosity function derived for the Ophiuchus cluster is virtually identical with that observed for other young clusters. The reddening law in this dense, dark-cloud region, derived from our photometry, is significantly different from the interstellar mean; R, the ratio of total to selective extinction, is larger, suggesting a particle-size distribution peaked toward larger sizes. Furthermore, the ice absorption feature at 3.05 has been observed for two sources in this region. The observed strength of this feature seems consistent with the range found for other dense, dark clouds. Subject headings: infrared sources - interstellar extinction - nebulae - open clusters