Abstract We present a comprehensive study of star formation toward the H II region Sharpless 155 (S155). Star-formation activities therein were investigated based on multi-wavelength data from optical to the far-infrared. The surface density distribution of selected 2MASS sources toward S155 indicates the existence of a compact cluster, which is spatially consistent with the position of the exciting source of the H II region, HD 217086. A sample of more than 200 sources with excessive emission in the infrared were selected based on their 2MASS color indices. The spatial distribution of the sample sources reveals the existence of three young subclusters in this region, among which subcluster A is spatially coincident with the bright rim of the H II region. In addition, photometric data from the WISE survey were used to identify and classify young stellar objects (YSOs). To further explore the evolutionary stages of the candidate YSOs, we fit the spectral energy distributions of 44 sources, which led to the identification of 14 Class I, 27 Class II and 3 Class III YSOs. The spatial distribution of the classified YSOs at different evolutionary stages presents a spatiotemporal gradient, which is consistent with a scenario of sequential star formation. On the other hand, Herschel PACS observations toward the interface between S155 and the ambient molecular cloud disclose an arc-shaped dust layer, the origin of which could be attributed to the UV dissipation from early type stars, e.g. HD 217061, in S155. Four dusty cores were revealed by the Herschel data, which hints at new generations of star formation.
Keywords ISM: H infrared: stars II regions --- stars: formation — stars: pre-main sequence
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