Gem OB1

The Gem OB1 association is one of the most massive molecular cloud complexes in the outer Galaxy. The distance to Gem OB1 is 2 kpc, and the molecular gas covers a region about 175 pc × 220 pc. The estimated mass of this complex is 3 × 10 solar masses.

The figure below presents a schematic of various optical components of Gem OB1 overlayed on a coarse contour map of the CO emission. The dark circles represent the approximate sizes and locations of catalogued nebulae, supernova remnants, and open clusters; the asterisks show the positions of possible members of the Gem OB1 association. The dotted line marks the extent of the region mapped in ¹²CO. The optical nebulae found within the body of the molecular gas include the supernova remnant IC 443, the bipolar reflection nebula Lk H 208, and the H II regions BFS 52, S 247, S 252, the S 254, S 255, S 256, S 257, & S 258 group. S 259, and S 261.

The Gem OB1 molecular cloud was mapped in ¹²CO(J=1-0)

and ¹³CO(J=1-0)

using the QUARRY receiver on the FCRAO 14m telescope. Each image contains over 160,000 spectra. These are two of the largest maps ever made of a single molecular cloud complex.

The ¹²CO and ¹³CO images reveal an intricate structure to the molecular gas around Gem OB1. Numerous rings and loops of gas are seen throughout the map on all size scales. Several of the more prominent structures seen in these images appear to have been created by expanding HII regions or stellar winds associated with S 247, S 252 and S 254--S 258. The combination of ¹²CO and ¹³CO data are powerful tools with which to analyze the excitation temperature and column density of the molecular gas. See also the images of S 235