Document Type

Article

Publication Date

10-1-2004

Publication Title

The Astrophysical Journal

Publisher

The American Astronomical Society

Abstract

Although Li has been extensively observed in main-sequence field and cluster stars, there are relatively fewer observations of Be. We have obtained Keck HIRES spectra of 36 late F and early G dwarfs in order to study the Li-Be correlation we found previously in the temperature regime of 5900–6650 K. The sample size for this temperature range with detectable and (usually) depleted Li and Be is now 88, including Li and Be abundances in both cluster and field stars. Therefore we can now investigate the influence of other parameters such as age, temperature, and metallicity on the correlation. The Be spectra at 3130 8 were taken over six nights from 1999 November to 2002 January and have a spectral resolution of $48,000 and a median signal-to-noise ratio (S/N) of 108 pixelÀ1. We obtained Li spectra of 22 stars with the University of Hawaii 88 inch (2.2 m) telescope and coude´ spectrograph with a spectral resolution of $70,000 and a median S/N of 110 pixelÀ1. We have rede-termined the effective temperatures for all the stars and adopted other parameters from published data or empirical relations. The abundances of both Li and Be in the stars we observed were determined from spectrum synthesis with MOOG 2002. The previously observed Li equivalent widths for some of our Be stars were used with the new temperatures and MOOG 2002 in the ‘‘blends’’ mode. For the 46 field stars from this and earlier studies we find a linear relation between A(Li) and A(Be) with a slope of 0:375 Æ0:036. Over the Teff range 5900–6650 K, we find the modest scatter about the Be-Li relation to be significantly correlated with Teff and perhaps also [Fe/H]. Dividing the sample into two temperature regimes of 6300–6650 K (corresponding to the cool side of the Li-Be dip) and 5900–6300 K (corresponding to the Li ‘‘plateau’’) reveals possible small differences in the slopes for the two groups, 0:404 Æ0:034 and 0:365 Æ0:049, respectively. When we include the cluster stars (Hyades, Pleiades, Praesepe, UMa Group, and Coma), the slope for the full temperature range (88 stars) is essentially the same, at 0:382 Æ0:030, as for the field stars alone. For the hotter temperature group of 35 Li-Be dip stars in the field and in clusters the slope is higher, at 0:433 Æ0:036, while for the cooler star group (54 stars) the slope is 0:337 Æ0:031, different by more than 1 . This small difference in the slope is predicted by the theory of rotationally induced mixing. The four stars with [Fe/H] less than À0.4 are all below the best-fit relation, i.e., there is more Be depletion at a given A(Li) or less Be ab initio. The youngest stars, i.e., Pleiades, have less depletion of both Li and Be. This too is predicted by rotationally induced slow mixing. Combining the Be results from both field and cluster stars, we find that there are stars with undepleted Be, i.e., near the meteoritic values of 1.42 dex, at all temperatures from 5500 to 6800 K. Depletions of Be of up to and even exceeding 2 orders of magnitude are common between 6000 and 6700 K.

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