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Session 43 - The Diffuse ISM: Milky Way and Beyond.
Display session, Tuesday, June 11
Great Hall,

[43.08] First Results from WHAM. I. H\alpha from HVCs, He I \lambda5876 from the WIM, and the First WIM Temperature Measurement.

S. L. Tufte, R. J. Reynolds, L. M. Haffner, K. P. Jaehnig (U. Wisconsin, Madison)

The Wisconsin H-Alpha Mapper (WHAM) instrument saw first light in January of 1996 and has been collecting unique data ever since. The WHAM instrument will move to Kitt Peak in Arizona in the late fall to make velocity-resolved maps of the entire northern sky in H\alpha at 10 km s^-1 spectral resolution and one-degree spatial resolution. During this year we are developing the remote operations capabilities of WHAM as well as using clear nights to collect data to complement the survey. The WHAM instrument contains a large-aperture, double-etalon Fabry-Perot spectrometer and utilizes a CCD camera to image the resulting ring pattern. We have shown that this technique yields a factor of 50 to 100 gain in efficiency over our previous spectrometer, which used a single-channel PMT detector. This dramatic increase in sensitivity has provided the opportunity to explore new terrain in the study of faint emission lines. We have clear detections of H\alpha emission from high-velocity clouds in Complex M. We have also detected He I \lambda5876 emission from the warm ionized component of the interstellar medium (WIM). This line results from recombination and thus probes the degree of helium ionization in this gas. Comparing the He I line intensity to the H\alpha intensity provides important constraints on the as yet unknown source of ionization of the WIM. Another interesting line we have detected in the WIM is the [N II] \lambda5755 line, which along with our measurement of the [N II] \lambda6584 line provides the first direct measurement of the temperature in the WIM. This work has been supported by the National Science Foundation.

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