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Session 24 - General Interstellar Medium.
Oral session, Monday, June 10
Historical Society,
We discuss serendipitous detections of diffuse ionized gas in high-resolution spectra of stars in Baade's Window, towards globular clusters near the Galactic center, and in extragalactic objects. Where diffuse ionized gas emits strongly, as it does near the centers of the Milky Way and Andromeda, its presence is often evident in a single two-hour echelle spectrum. The breadth of the emission features is always narrow, \leq 30 km/s FWHM, in the regions where it has been detected. Because breadths are narrow, the velocity signature of the gas is clearly discerned in the echelle spectra. In each case the kinematics of the gas is distinct from that of the target, indicating that the gas is not associated with the target. We estimate the effect of diffuse ionized gas on H\alpha and [N II] measurements at lower resolution, noting its effect on Balmer absorption-line indices and estimates of the presence of a young-star population.
