Research Note

On the opacity change required to compensate for the revised solar composition

¹ Department of Physics and Astronomy, Building 1520, Aarhus University, 8000 Aarhus C, Denmark e-mail: [jcd;fpp]@phys.au.dk
² INAF – IASF, Istituto di Astrofisica Spaziale e Fisica Cosmica, via Fosso del Cavaliere 100, 00133 Roma, Italy e-mail: mariapia.dimauro@iasf-roma.inaf.it
³ Institute of Astronomy, Madingley Road, Cambridge CB3 0HA, UK e-mail: hg@ast.cam.ac.uk

Received: 9 May 2008
Accepted: 26 October 2008

Abstract

Context. Recent revisions of the determination of the solar composition have resulted in solar models in marked disagreement with helioseismic inferences.

Aims. The effect of the inferred composition change on the models is largely caused by the change in opacity. Thus, we wish to determine an intrinsic opacity change that would compensate for the revision to the composition.

Methods. By comparing models computed with the old and revised compositions we determine the required opacity change. Models are computed with the opacity modified in this manner and used as reference in helioseismic inversions to determine the difference between the solar and model sound speed.

Results. An opacity increase ranging between around 30 per cent close to the base of the convection zone and a few percent in the solar core leads to a sound-speed profile, for the revised composition, that is essentially indistinguishable from the original solar model. As a function of the logarithm of temperature this is well represented by a simple cubic fit. The physical realism of such a change remains debatable, however.