Limits on the Boron Isotopic Ratio in HD 76932

Data in the λ2090 B region of HD 76932 have been obtained at a high signal-to-noise ratio using the Hubble Space Telescope Goddard High-Resolution Spectrograph echelle at a resolution of 90,000. This wavelength region has been previously identified as a likely candidate for observing the 11B/10B isotopic splitting. The observations do not match a calculated line profile extremely well at any abundance for any isotopic ratio. If the B abundance previously determined from observations at λ2500 is assumed, the calculated line profile is too weak, indicating a possible blending line. Assuming that the absorption at λ2090 is entirely due to boron, the best-fit total B abundance is higher than, but consistent with, that obtained at λ2500, and the best-fit isotopic ratio (11B/10B) is in the range ~10:1 to ~4:1. If the absorption is not entirely due to B and there is an unknown blend, the best-fit isotopic ratio may be closer to 1:1. Future observations of a similar metal-poor star known to have unusually low B should allow us to distinguish between these two possibilities. The constraints that can be placed on the isotopic ratio based on comparisons with similar observations of HD 102870 and HD 61421 (Procyon) are also discussed.