The Molecular Clouds Associated with the H II Regions/Candidates between L = 207°7 and L = 211°7

Abstract

Using the PMO-13.7 m millimeter telescope at Delingha in China, we have conducted a large-scale simultaneous survey of ¹²CO, ¹³CO, and C¹⁸O J = 1 - 0 emission toward the sky region centered at l = 209°7, b = -2°25 with a coverage of 4°0 × 4°5. The majority of the emission in the region comes from the clouds with velocities lying in the range from -3 to 55 km s^-1, at kinematic distances from 0.5 to 7.0 kpc. The molecular clouds in the region are concentrated into three velocity ranges. The molecular clouds associated with the 10 H II regions/candidates are identified and their physical properties are presented. Massive stars are found within Sh2-280, Sh2-282, Sh2-283, and BFS54, and we suggest them to be the candidate excitation sources of the H II regions. The distributions of the excitation temperature and line width with the projected distance from the center of H II region/candidate suggest that the majority of the 10 H II regions/candidates and their associated molecular gas are three-dimensional structures, rather than two-dimensional structures.