The Boron Abundance of the Hyades Giants
Session 7 -- Stellar Abundances Across the H-R Diagram
Display presentation, Monday, 30, 1994, 9:20-6:30

## [7.02] The Boron Abundance of the Hyades Giants

D.K. Duncan (U. of Chicago and The Adler Planetarium), R.C.Peterson, J.A. Thorburn (U. of Chicago), M.H.Pinsonneault (Ohio State U.)

Spectra of two of the Hyades giants $\epsilon$ Tau (HD~28305) and $\delta^1$ Tau (HD~27697) and the K0II giant $\beta$ Gem (HD~62509) have been obtained with the G270M grating of the GHRS spectrograph of the Hubble Space Telescope . A Hyades main sequence F star near the turnoff was also observed. Boron abundances were determined from spectrum synthesis of the region near 2500\AA. Since B is destroyed by (p,$\alpha$) reactions at a temperature near 5 million degrees, its abundance probes deep internal mixing, mass loss, and depth of the convection zone of a giant star. We find that the B abundance in each giant is greatly reduced below solar. In order to more confidently determine an abundance and not just an upper limit, we carefully reanalyzed previous HST observations of F stars and also the Solar Maximum Mission solar spectrum, to identify the amount of line strength due to possible blending in the region of the B lines. Our final B abundance will be combined with previous abundance determinations of Li and Be to test models of the convection zone depth in giants, mass loss, and other predictions of stellar evolution models.