Wind Velocity and Density Laws for the Hybrid-Chromosphere Star $\alpha$ TrA obtained from GHRS Spectra
Session 5 -- Chromospheres/Coronae/Active Binaries
Display presentation, Monday, 30, 1994, 9:20-6:30

## [5.04] Wind Velocity and Density Laws for the Hybrid-Chromosphere Star $\alpha$ TrA obtained from GHRS Spectra

J.L. Linsky, G.M. Harper, B. Wood, A. Brown (JILA, Univ. Colorado \& NIST)

We have used the Goddard High Resolution Spectrometer on HST to study the wind of the hybrid-chromosphere star $\alpha$ TrA (K2 IIb-IIIa). The stellar wind is detected by the absorption seen against the chromospheric Mg II resonance lines (h and k) centered at 2795.53 \AA\ and 2802.70 \AA. Spectra obtained with the high spectral resolution ($\lambda/\Delta\lambda=84,750$) and low scattered light properties of the GHRS echelle grating reveal stellar Mg~II emission lines with complex interstellar absorption and a broad wind absorption feature centered at --90 km s$^{-1}$. We infer the Mg II opacity as a function of velocity and derive velocity laws for the stellar wind by comparing the observed line profiles with synthetic profiles computed for a range of wind parameters. We also discuss the origin of the observed broad lines of Si~III], C~III], and C~IV.

This work is supported by NASA Interagency Transfer S-56460-D to the National Institute of Standards and Technology.