ALMA OBSERVATIONS OF THE ORION PROPLYDS

摘要

We present Atacama Large Millimeter/submillimeter Array (ALMA) observations of protoplanetary disks ("proplyds") in the Orion Nebula Cluster. We imaged five individual fields at 856 μm containing 22 Hubble Space Telescope (HST)-identified proplyds and detected 21 of them. Eight of those disks were detected for the first time at submillimeter wavelengths, including the most prominent, well-known proplyd in the entire Orion Nebula, 114-426. Thermal dust emission in excess of any free-free component was measured in all but one of the detected disks, and ranged between 1 and 163?mJy, with resulting disk masses of 0.3-79 M jup. An additional 26 stars with no prior evidence of associated disks in HST observations were also imaged within the 5 fields, but only 2 were detected. The disk mass upper limits for the undetected targets, which include OB stars, θ1?Ori?C, and θ1?Ori F, range from 0.1 to 0.6?M jup. Combining these ALMA data with previous Submillimeter Array observations, we find a lack of massive (3?M jup) disks in the extreme-UV-dominated region of Orion, within 0.03?pc of θ1?Ori?C. At larger separations from θ1?Ori?C, in the far-UV-dominated region, there is a wide range of disk masses, similar to what is found in low-mass star forming regions. Taken together, these results suggest that a rapid dissipation of disk masses likely inhibits potential planet formation in the extreme-UV-dominated regions of OB associations, but leaves disks in the far-UV-dominated regions relatively unaffected.