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Session 24 - General Interstellar Medium.
Oral session, Monday, June 10
Historical Society,

[24.04] Diffuse Ionized Gas Line Strengths from Echelle Spectroscopy

D. M. Terndrup, R. C. Peterson (Ohio State, UCO/Lick)

We discuss serendipitous detections of several emission lines from the diffuse interstellar medium in high-resolution spectra of stars in Baade's Window and globular clusters near the Galactic center. Following Lehnert amp; Heckman (1994, ApJ, 426, L27), we show that the ratios of the strengths of the emission lines of H\alpha, [N II], and [S II] are inconsistent with those of H II regions, but match those of the diffuse ionized gas, suggesting this as its origin. We discuss these ratios and upper limits to the line strengths of [O I] \lambda6300 and He I \lambda5879. It is difficult to specify where the emitting gas is located along the line of sight to Baade's Window, since this is along the Galaxy's minor axis where the (low) gas velocity poses no constraint. However, we note that the two spectra acquired 1 arcmin apart in Baade's Window are indistinguishable, with equal line strengths and velocity widths. The emission lines are significantly fainter in the sky spectrum of a star in the globular cluster NGC 5927, where the gas velocity indicates that the emission probably does arise in or near the galactic disk.

Program listing for Monday