Study of L 688/L 694/L 700: a Complex of Dark Clouds in Aquila

Abstract

We present the results of optical and radio molecular observations of the small dark clouds L 688, L 694, and L 700 (CB 200). Based on star counts, we found a distance of $230 \pm 30\,\mathrm{pc}$ for the clouds. We present extinction maps of the clouds based on the USNO Catalog data. Our objective prism search for candidate pre-main-sequence stars resulted in the detection of an $\mathrm{H}\alpha$ emission star in the cloud area. We observed the clouds in the 12CO ($1\hbox{-}0$), and $\mathrm{C}{{18\atop} \mathrm{O}}$ ($1\hbox{-}0)$ lines. A ring-shaped cloud of $\sim 430\,{{{M}_{\odot}}}$ was detected from the 12CO observation. Five 13CO cores were identified. Three $\mathrm{C}{{18\atop} \mathrm{O}}$ cores with $N(\mathrm{H}_{2}) \sim (5.3\hbox{-}7.6) \times 10^{21}\mathrm{cm}^{-2}$ reside in two of the 13CO cores in the northern part of the cloud. The density gradient seen in optical, infrared and radio, and also the positions of the star-formation sites may suggest the possibility of shock compression due to some stars or SNRs near the galactic plane.