The solar photospheric nitrogen abundance

Analysis of atomic transitions with 3D and 1D model atmospheres

¹ GEPI, Observatoire de Paris, CNRS, Université Paris Diderot, 92195 Meudon Cedex, France e-mail: Elisabetta.Caffau@obspm.fr
² Department of Physics, University of Perugia, via Pascoli, 06123 Perugia, Italy
³ CIFIST Marie Curie Excellence Team, France
⁴ Istituto Nazionale di Astrofisica, Osservatorio Astronomico di Trieste, via Tiepolo 11, 34143 Trieste, Italy
⁵ Dipartimento di Astronomia, Università degli Studi di Trieste, via G.B. Tiepolo 11, 34143 Trieste, Italy
⁶ Astrophysikalisches Institut Potsdam, An der Sternwarte 16, 14482 Potsdam, Germany
⁷ Kapteyn Astronomical Institute, Postbus 800, 9700 AV Groningen, The Netherlands
⁸ Istituto Nazionale di Fisica Nucleare, section of Perugia, via Pascoli, 06123 Perugia, Italy

Received: 26 August 2008
Accepted: 28 January 2009

Abstract

Context. In recent years, the solar chemical abundances have been studied in considerable detail because of discrepant values of solar metallicity inferred from different indicators, i.e., on the one hand, the “sub-solar” photospheric abundances resulting from spectroscopic chemical composition analyses with the aid of 3D hydrodynamical models of the solar atmosphere, and, on the other hand, the high metallicity inferred by helioseismology.

Aims. After investigating the solar oxygen abundance using a CO⁵BOLD 3D hydrodynamical solar model in previous work, we undertake a similar approach studying the solar abundance of nitrogen, since this element accounts for a significant fraction of the overall solar metallicity, Z.

Methods. We used a selection of atomic spectral lines to determine the solar nitrogen abundance, relying mainly on equivalent width measurements in the literature. We investigate the influence on the abundance analysis, of both deviations from local thermodynamic equilibrium (“NLTE effects”) and photospheric inhomogeneities (“granulation effects”).

Results. We recommend use of a solar nitrogen abundance of A(N) = 7.86 ± 0.12, whose error bar reflects the line-to-line scatter.

Conclusions. The solar metallicity implied by the CO⁵BOLD-based nitrogen and oxygen abundances is in the range . This result is a step towards reconciling photospheric abundances with helioseismic constraints on Z. Our most suitable estimates are and .