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Session 15 - Interstellar Medium I.
Display session, Monday, January 15
North Banquet Hall, Convention Center

[15.06] X-ray Shadows of Infrared Cirrus and the Local Hot Interstellar Medium

Q. D. Wang (Northwestern U.)

The Sun is located in a region which is filled largely with low-density, X-ray-emitting gas. However, how far this region extends is not yet clear, and basic properties of the hot gas, such as the temperature, is still poorly constrained. A powerful technique to probe the hot gas is to examine x-ray absorptions (shadows) produced by cool gas clouds whose distances can be determined. We are conducting a systematic study of x-ray shadows in the 0.1-0.3 range. This study consists of three major steps: a search for the shadows cast by infrared cirrus clouds, using the ROSAT and IRAS archives; (2) multi-energy band measurements of local and distant x-ray intensities relative to the clouds; and (3) estimates of x-ray absorptions and distances to the clouds, using optical/UV/EUV extinction and absorption line observations of foreground and background stars of known distances. In a pilot project (Wang amp; Yu, 1995, AJ, 109, 698), we have found that anti-correlation between infrared emission from cirrus clouds and background X-ray intensity is present in all five fields we have examined, indicating that a considerable number of degree-size, X-ray-absorbing gas clouds are embedded in the X-ray-emitting medium around the Sun. I will present new results from this study. In particular, I will report a measurement of the temperature, pressure, and line-of-sight distribution of the hot gas. Our goal is to construct a 3-D picture of the hot gas in the solar neighborhood and to clarify the origin of the gas.

Program listing for Monday