EDP Sciences
Free access
Volume 417, Number 2, April II 2004
Page(s) 769 - 774
Section The Sun
DOI http://dx.doi.org/10.1051/0004-6361:20034329

A&A 417, 769-774 (2004)
DOI: 10.1051/0004-6361:20034329

Line formation in solar granulation

V. Missing UV-opacity and the photospheric Be abundance
M. Asplund

Research School of Astronomy and Astrophysics, Mount Stromlo Observatory, Cotter Road, Weston, ACT 2611, Australia
(Received 17 September 2003 / Accepted 3 November 2003)

The possibility of unaccounted for opacity sources in the UV for late-type stars has often been invoked to explain discrepancies between predicted and observed flux distributions and spectral line strengths. Such missing UV-opacity could among other things have a significant impact on abundance determination for elements whose only relevant spectral features are accessible in this wavelength region, such as Be. Here, the study by Balachandran & Bell (1998) is re-visited in the light of a realistic 3D hydrodynamical solar model atmosphere and the recently significantly downward revised solar O abundance obtained with the same model atmosphere. The amount of missing UV-opacity, if any, is quantified by enforcing that the OH A-X electronic lines around 313 nm produce the same O abundance as the other available diagnostics: OH vibration-rotation and pure rotation lines in the IR, the forbidden [O I] 630.0 and 636.3 nm lines and high-excitation, permitted O I lines. This additional opacity is then applied for the synthesis of the Be II line at 313.0 nm to derive a solar photospheric Be abundance in excellent agreement with the meteoritic value, thus re-enforcing the conclusions of Balachandran & Bell. The about 50% extra opacity over accounted for opacity sources can be well explained by recent calculations by the Iron Project for photo-ionization of Fe I.

Key words: convection -- line: formation -- Sun: abundances -- Sun: granulation -- Sun: photosphere

© ESO 2004