Abstract
Data from the Canadian Galactic Plane Survey reveal an abundance of H I shells and arcs in the disk of our galaxy. While their shape suggests the influence of stellar winds or supernovae, very few of these structures have been examined in detail thus far. A fine example is an H I shell in the outer Galaxy with no continuum counterpart, discovered in the survey's pilot project. Its size and kinematics suggest that it was created by the winds of a single late-type O star that has since evolved off the main sequence, or by a supernova explosion. A B1 Ia star at the center of the shell, in projection, is a possible candidate for the energy source if the shell is assumed to be windblown. The shell's shape implies a surprisingly small scale height of less than about 30 pc for the surrounding gas if the elongation is due to evolution in a density gradient.
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