CHIPS Questions and Answers

The CHIPS band contains the significant majority of the radiated power from diffuse hot interstellar plasma in its most probable temperature range. Although X-ray and UV studies can detect plasma at greater distances and map it with better angular resolution, extrapolation of such measurements to a total plasma luminosity will be fraught with significant uncertainty until spectroscopic observations of diffuse emission are carried out in the CHIPS band.

Can observations with CHIPS disentangle all of the cooling mechanisms that might be taking place in the local interstellar medium?

The various cooling mechanisms make observationally distinct predictions for the emission in the CHIPS band. In combination with observations of emission and absorption features at other wavelengths, CHIPS data will be extremely helpful in disentangling these processes. CHIPS will do an excellent job of constraining the electron temperature through measurement of collisionally excited line emission. Determination of the electron temperature is a crucial step in understanding the cooling process.

Do current observational limits in the CHIPS band set interesting constraints on the physical properties of plasma in the local bubble?

No. Current observational limits were set using instruments with limited spectral resolution and many are well above the expected emission-line fluxes. The marginal detection in 18 million seconds of EUVE observations in regions where the soft X-rays are bright does indicate that diffuse emission is present in our band.

What if the foreground absorption column is higher than you have estimated?

With nominal assumption, the bright iron emission lines will be detected at 20 to 50 in each sky resel. A higher absorption would reduce the line flux, but, barring some wholly unexpected distribution of the local neutral material, absorption will reduce the EUV emission to undetectable levels in only a limited number of viewing directions. The CHIANTI CIE plasma model predicts somewhat brighter peak iron line fluxes than the Raymond & Smith code used in our analysis.