Session 56 - Frontiers of Ultraviolet Astrophysics.
Display session, Wednesday, June 10
Atlas Ballroom,

## [56.02] Simulations of FUSE spectra of A-type and cooler stars: D/H and warm plasma emission

D. O'Neal, J. L. Linsky (JILA/U. Colorado)

The Far Ultraviolet Spectroscopic Explorer (FUSE) will observe many stars in the 905--1187 Å\ spectral region with a resolving power of 24,000--30,000. FUSE will explore this critically important spectral region, which is mostly inaccessible to HST (and previously to IUE), observing sources much fainter than Copernicus and with much better spectral resolution than HUT or ORFEUS.

We present simulations of stellar spectra that will be observed with FUSE. The FUSE bandpass includes the Ly \beta (1025 Å\ and Ly \gamma (972 Å\ lines. Extrapolating from GHRS Ly \alpha spectra, we simulate FUSE spectra of the Ly \beta and Ly \gamma lines of Capella and some other late-type stars. These simulations will address the accuracy with which the interstellar D/H ratio can be measured using these lines.

In addition, one of our FUSE observing programs will measure for the first time the amount of warm (60,000--300,000 K) plasma present in the outer atmospheres of A and early-F stars, using the C III 977 Å\ and O VI 1032 Å\ lines. This program will explore whether the outer atmospheric layers of these stars are heated to these temperatures and whether the heating process is magnetic or acoustic. Our simulations indicate that FUSE will be sensitive enough to measure very low luminosities in these lines.

This work is supported by NASA grants to the University of Colorado.