The Boron Abundances of 110 Her and 45 Tau

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Session 7 -- Stellar Abundances Across the H-R Diagram
Display presentation, Monday, 30, 1994, 9:20-6:30

[7.03] The Boron Abundances of 110 Her and 45 Tau

J.A.\ Thorburn, D.K.\ Duncan (UChicago), \& R.C.\ Peterson (Lick Observatory \& UChicago)

New low noise, HST High Resolution Spectrometer boron B I $\lambda2496$ observations are presented of the F6 subgiant 110 Her and the Hyades F2 dwarf 45 Tau (vB 14). 45 Tau has previously been shown to have normal lithium and beryllium abundances for a Hyades F2 star. In contrast, 110 Her is deficient in lithium by more than two orders of magnitude and in beryllium by roughly a factor of 10. The effective temperature of 110 Her (6350 K) is considerably cooler than a classical Hyades lithium gap star (6600 K).

We show that the surface boron abundance of 110 Her is almost identical to what is observed in Procyon, used as an empirical standard. Procyon is known to be deficient in boron by about a factor of two (Lemke et al.\ 1993, PASP, 105, 468) relative to other stars of its temperature and composition, and it is about 0.2 dex more metal-rich than 110 Her. If initial boron content in Pop.\ I stars scales with metallicity, then 110 Her may show an undepleted surface boron abundance. 45 Tau appears to display a somewhat higher boron abundance, which is presumably unaltered from its initial, pre-stellar value. These observations will be compared to predictions of stellar models which include microscopic diffusion and rotational mixing.

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