Star Formation in the Cepheus Flare Molecular Clouds. I. Distance Determination and the Young Stellar Object Candidates

Abstract

Results of an objective prism Schmidt survey are combined with IRAS survey data in order to assess the star-forming activity in the Cepheus Flare, a nearby giant molecular cloud complex at ~+15° above the Galactic equator. The distribution of absorbing matter along the line of sight was also studied. The Wolf diagrams, displaying the cumulative distribution of field star distance moduli, show that the interstellar matter in this region is concentrated at three characteristic distances: 200, 300, and 450 pc. The three components, though partly overlapping, can be separated along the Galactic latitude. Within the area of the Cepheus Flare, distances are determined for 14 Lynds dark clouds and for some other clouds. In order to compile a sample of young stellar object (YSO) candidates, three types of star formation signposts were searched for the following: 1. Prestellar cores in the IRAS 100 μm optical depth image of the region, 2. Far-infrared sources representing embedded YSOs and optically visible pre-main-sequence star candidates using IRAS Point Source Catalog, Faint Source Catalog, and calibrated IRAS detector scans, 3. Hα emission stars appearing on low-dispersion objective prism Schmidt plates as candidate pre-main-sequence stars. The IRAS 100 μm optical depth image of the region revealed 107 dense cores. Most of them are probably starless cores and, as such, potential sites of future star formation. One hundred twenty-two IRAS point sources were selected as probable YSOs at various evolutionary stages. An objective prism search for Hα emission stars covering an area of about 150 deg2 resulted in the detection of 142 Hα emission stars. Infrared fluxes taken from the IRAS catalogs or determined from the detector scans are listed for 95 of them. This sample is expected to consist of mostly T Tauri stars associated with the cloud complex. Finding charts and catalogs of the young stellar object candidates are also given. These results may serve as a basis for further dedicated studies of the region and will be useful for comparison when star-forming activity in other cloud complexes is investigated.