Possible Young Stellar Objects without Detectable CO Emission

We found that at least 18 Young Stellar Object candidates invisible atoptical and near-infrared wavelengths, as well as ^12CO emission. They are IRASpoint sources with FIR colors similar to those of usual YSOs, and the infraredspectral indices between 2.2 um and 25 um correspond to those of class I YSOs.These peculiar far-infrared objects are highly concentrated around the galacticplane and the distances are estimated to be around 1 kpc. Although theirdistribution is away from molecular clouds, some of them seem to be associatedwith large dark clouds or weak radio sources.Comment: 10 pages with 4 figures, LaTeX, accepted for publication in PASJ. Images(fig2) are included in source file as JPEG files. PDF files are avilable at ftp.kusastro.kyoto-u.ac.jp/pub/iwata/preprint