Beryllium in F and G field dwarfs from high-resolution Canada-France-Hawaii telescope spectra.
BOESGAARD A.M., DELIYANNIS C.P., KING J.R. and STEPHENS A.
Abstract (from CDS):
It is important to add observations of Be to the huge arsenal of Li observations in order to identify the mechanisms operating in stellar interiors that alter the surface composition of the light elements. Beryllium is more resistant to destruction than is Li, so information on the abundances of both Li and Be reveals more information on the internal processes than either element does alone. We have made observations of Be II at 3131 Å in 46 solar-type stars from the Canada-France-Hawaii Telescope with high spectral resolution and high signal-to-noise ratios (S/N). Our Li I 6707 Å data for 39 of these stars come from our high-resolution, high-S/N observations with the University of Hawai`i 88 inch (2.2 m) telescope and coudé spectrograph and Keck I High Resolution Echelle Spectrometer and, for six stars, from the literature. Most of the stars in our sample are F and G dwarfs with Teff between 6100 and 6600 K and with [Fe/H] between -0.6 and +0.2. The abundances of Be have been determined through spectrum synthesis, while Li has been analyzed as a blend to find the Li abundance. We find a large range in both Li and Be in these stars; for Be it is at least 2.5 dex and for Li at least 3 dex. However, there is an excellent correlation between Li and Be, as discovered by Deliyannis et al. from a smaller sample. We find that in the range of Teff of 5850 K (near the Li ``peak'' in open clusters) to 6680 K (at the bottom of the Li ``gap'' as defined by the Hyades), Li and Be appear to be depleted together. The slope of this remarkable logarithmic relation is 0.36: as Li is reduced by a factor of 10, Be is reduced by only 2.2 times. There is some scant evidence for a change in the slope between the cooler stars and the hotter stars such that the cooler stars deplete more Li relative to Be than the hotter stars. These results are well matched by models that incorporate rotationally induced slow mixing of the stellar surface material with the deeper layers of the star.