The photospheric solar oxygen project^*

I. Abundance analysis of atomic lines and influence of atmospheric models

¹ GEPI, Observatoire de Paris, CNRS, Université Paris Diderot, 92195 Meudon Cedex, France e-mail: Elisabetta.Caffau@obspm.fr
² CIFIST Marie Curie Excellence Team
³ Astrophysikalisches Institut Potsdam, An der Sternwarte 16, 14482 Potsdam, Germany
⁴ Center for Astrophysics and Space Astronomy, University of Colorado 389 UCB (CASA), Boulder, CO 80309-0389, USA
⁵ Istituto Nazionale di Astrofisica, Osservatorio Astronomico di Trieste, via Tiepolo 11, 34143 Trieste, Italy
⁶ GEPI, Observatoire de Paris, CNRS, Université Paris Diderot, 61 Av. de l'Observatoire, 75014 Paris, France
⁷ CRAL,UMR 5574: CNRS, Université de Lyon, École Normale Supérieure de Lyon, 46 allée d'Italie, 69364 Lyon Cedex 7, France
⁸ Department of Physics and Astronomy, Uppsala University, Box 515, 751 20 Uppsala, Sweden
⁹ GRAAL, CNRS UMR 5024, Université Montpellier II, 34095 Montpellier Cedex 5, France

Received: 1 April 2008
Accepted: 28 May 2008

Abstract

Context. The solar oxygen abundance has undergone a major downward revision in the past decade, the most noticeable one being the update including 3D hydrodynamical simulations to model the solar photosphere. Up to now, such an analysis has only been carried out by one group using one radiation-hydrodynamics code.

Aims. We investigate the photospheric oxygen abundance considering lines from atomic transitions. We also consider the relationship between the solar model used and the resulting solar oxygen abundance, to understand whether the downward abundance revision is specifically related to 3D hydrodynamical effects.

Methods. We performed a new determination of the solar photospheric oxygen abundance by analysing different high-resolution high signal-to-noise ratio atlases of the solar flux and disc-centre intensity, making use of the latest generation of CO5BOLD 3D solar model atmospheres.

Results. We find . The lower and upper values represent extreme assumptions on the role of collisional excitation and ionisation by neutral hydrogen for the NLTE level populations of neutral oxygen. The error of our analysis is ± (0.04± 0.03) dex, the last being related to NLTE corrections, the first error to any other effect. The 3D “granulation effects” do not play a decisive role in lowering the oxygen abundance.

Conclusions. Our recommended value is , considering our present ignorance of the role of collisions with hydrogen atoms on the NLTE level populations of oxygen. The reasons for lower O abundances in the past are identified as (1) the lower equivalent widths adopted and (2) the choice of neglecting collisions with hydrogen atoms in the statistical equilibrium calculations for oxygen.