  We report on observations of several optical emission lines toward a variety
of newly revealed faint, large-scale Halpha-emitting regions in the Galaxy. The
lines include [NII] 6583, [NII] 5755, [SII] 6716, [OIII] 5007, and HeI 5876
obtained with the Wisconsin H-Alpha Mapper (WHAM) toward sightlines that probe
superbubbles, high latitude filamentary features, and the more diffuse warm
ionized medium (WIM). Our observations include maps covering thousands of
square degrees toward the well-known Orion-Eridanus bubble, a recently
discovered 60deg x 20deg bipolar superbubble centered in Perseus, plus several
classical HII regions surrounding OB stars and hot evolved stellar cores. We
use the emission line data to explore the temperature and ionization conditions
within the emitting gas and their variations between the different emission
regions. We find that in the diffuse WIM and in the faint high latitude
filamentary structures the line ratios of [NII]/Ha and [SII]/Ha are generally
high, while [OIII]/Ha and HeI/Ha are generally low compared to the bright
classical HII regions. This suggests that the gas producing this faint
wide-spread emission is warmer, in a lower ionization state, and ionized by a
softer spectrum than gas in classical HII regions surrounding O stars, the
presumed ionization source for the WIM. In addition, we find differences in
physical conditions between the large bubble structures and the more diffuse
WIM, suggesting that the ionization of superbubble walls by radiation from
interior O associations does not account entirely for the range of conditions
found within the WIM, particularly the highest values of [NII]/Ha and [SII]/Ha.

Astrophysics