SEQUENTIAL STAR FORMATION IN THE Sh 254-258 MOLECULAR CLOUD: HEINRICH HERTZ TELESCOPE MAPS OF CO J = 2-1 AND 3-2 EMISSION

摘要

The molecular cloud associated with the Sh 254-258 group of five small H II regions appears to be forming a (late)-OB association. We have mapped the associated molecular cloud in the J = 2-1 line of the CO and 13CO molecules over 075 × 1°, and the CO J = 3-2 line toward the two main peaks, with the University of Arizona Heinrich Hertz Submillimeter Telescope. The data are analyzed with a statistical equilibrium code to estimate physical properties of the molecular gas. We compare the molecular cloud morphology with images at optical, IR, and radio wavelengths. From this analysis, we propose a scenario for sequential formation of the stars exciting the H II regions, triggered by the compression of the molecular gas as a consequence of the expansion of the adjacent H II regions.