An H-alpha emission-line survey of the rho Ophiuchi dark cloud complex

Abstract

Our analysis of two H-alpha objective-prism plates covering about 40 square degrees and including most of the nearby rho Ophiuchi cloud complex is presented. These data provide a high-resolution, completely sampled survey of stars in the T Tauri phase of pre-main-sequence evolution in the lower-extinction regions of the dark cloud. Detailed finder charts and accurate positions for 86 sources of definite or probable H-alpha emission are presented, making this survey useful for future studies of global star formation in the rho Oph clouds. In addition, the first Herbig-Haro object candidates in this area has been found. The correspondence of the emission-line stars with the densest molecular gas and known T Tauri stars, X-ray sources, and IRAS point sources suggest that most of the stars in our sample are indeed young stellar objects. Comparing the number of these objects in the main cloud core with the total number of association members suggests that about 25 percent of the association members are currently observed in the T Tauri phase of evolution near the surface of the cloud. The preponderance of emission-line stars in the western regions of the complex may imply a critical density necessary for star formation to occur or perhapsmore » an actual progression of star formation through the complex. 27 references.« less