A Determination of the Solar Photospheric Boron Abundance

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Abstract
We present a reanalysis of the B I λ2496.771 line in the solar photosphere using up-to-date line lists, new atomic data, and employing LTE spectrum synthesis. Adopting the two most recent values for the photoionization cross section for Mg I 3p 3Po (the dominant continuous opacity source in this spectral region), along with two different types of model atmospheres, we find a mean photospheric boron abundance of log (B)=2.70, with estimated statistical uncertainties of -0.12 and 0.21 dex. For all cases investigated, we find tolerable spectrum synthesis fits to the nearby Fe I line at 2496.533 Å, which has a well-determined laboratory gf-value. With the adopted Mg I cross sections we find much better agreement between the predicted model and observed continuum intensities at the solar limb, which is in contrast to results from earlier studies. In addition, as a check on the boron abundance derived from the ultraviolet B I line we analyze the weak, excited B I transition at 16244.670 Å. This line is marginally detected and the derived value of log (B)=2.55±0.2 is not in disagreement with the UV abundance, but is significantly larger than previous upper-limit estimates from infrared spectra. The results obtained for the photospheric boron abundance are within the errors identical to the accepted meteoritic value of 2.78±0.05: we find no measurable boron depletion in the solar photosphere.