NEAR-INFRARED IMAGING SURVEY OF YOUNG STELLAR OBJECTS IN BOK GLOBULES

We performed a near-infrared imaging survey toward 34 Bok globules con taining IRAS point sources, which were young stellar objects (YSOs) ca ndidates. We used state-of-the-art NICMOS 3 and SQIID cameras for this survey. Visual examination of the images revealed that 20 globules sh owed evidence of nebular emission or very red stellar objects located at the position of the YSO candidates. The IRAS 12/25 mum spectral ind ices of these 20 objects are distinctively different from those of the 14 globules which showed no nebulosity, in the sense that more than 5 0% of the 20 nebular or very red objects have negative IRAS 12/25 mum spectral indices, while only 20% of the 14 non-nebular objects show su ch red IRAS colors. Analysis of the near-infrared nebulosities present in the images revealed the following: (1) these nebulosities generall y contain a stellarlike source surrounded by an extended component; (2 ) several possible binaries with separations of about 10'' were found to reside in common infrared nebulosity; (3) infrared reflection nebul ae, seen at 2.2 mum, are good tracers of CO mass outflow morphology. T he objects displaying nebulosities, when ordered by their increasing 1 2/25 mum indices, seems to form an evolutionary sequence. Large negati ve 12/25 mum indices seem to indicate objects deeply embedded in their clouds (by showing nebulosities mostly in the K band, having associat ed molecular outflows, and no optical counterparts). As these objects reach later stages of their pre-main-sequence evolution (by showing ne bulosity in the J band only, no detected molecular outflow, and having optical counterparts or optical nebulae), their 12/25 mum indices inc rease and become positive.