The solar photospheric silicon abundance according to CO⁵BOLD

Abstract

Context. In this work, we present a photospheric solar silicon abundance derived using CO 5 BOLD model atmospheres and the LINFOR3D spectral synthesis code. Previous works have differed in their choice of a spectral line sample and model atmosphere as well as their treatment of observational material, and the solar silicon abundance has undergone a downward revision in recent years. We additionally show the effects of the chosen line sample, broadening due to velocity fields, collisional broadening, model spatial resolution, and magnetic fields. Aims. Our main aim is to derive the photospheric solar silicon abundance using updated oscillator strengths and to mitigate model shortcomings such as over-broadening of synthetic spectra. We also aim to investigate the effects of different line samples, fitting configurations, and magnetic fields on the fitted abundance and broadening values. Methods. CO 5 BOLD model atmospheres for the Sun were used in conjunction with the LINFOR3D spectral synthesis code to generate model spectra, which were then fit to observations in the Hamburg solar atlas. We took pixel-to-pixel signal correlations into account by means of a correlated noise model. The choice of line sample is crucial to determining abundances, and we present a sample of 11 carefully selected lines (from an initial choice of 39 lines) in both the optical and infrared, which has been made possible with newly determined oscillator strengths for the majority of these lines. Our final sample includes seven optical Si i lines, three infrared Si i lines, and one optical Si ii line. Results. We derived a photospheric solar silicon abundance of log ε Si = 7.57 ± 0.04, including a −0.01 dex correction from Non-Local Thermodynamic Equilibrium (NLTE) effects. Combining this with meteoritic abundances and previously determined photospheric abundances results in a metal mass fraction Z/X = 0.0220 ± 0.0020. We found a tendency of obtaining overly broad synthetic lines. We mitigated the impact of this by devising a de-broadening procedure. The over-broadening of synthetic lines does not substantially affect the abundance determined in the end. It is primarily the line selection that affects the final fitted abundance.

Solar Models and Astrophysical S-factors Constrained by Helioseismic Results and Updated Neutrino Fluxes

“…The estimations of the metal abundance are related to the chemical element abundances of the Sun that are still under hot debate since Lodders (2003) and Asplund et al (2005) revised the ratio of metal abundance to hydrogen abundance of the solar photosphere, (Z/X) s , from the old 0.023 (Grevesse & Sauval 1998, hereafter GS98) to 0.0177 or 0.0165. So far, the value of the ratio has been revised several times (Lodders et al 2009;Asplund et al 2009Asplund et al , 2021Caffau et al 2010Caffau et al , 2011Lodders et al 2020;Amarsi et al 2021;Magg et al 2022;Deshmukh et al 2022). The helium abundance, Y s , in the solar convection zone (CZ) and thus the photosphere and the radius of the base of the CZ (BCZ), r cz , are determined by helioseismology.…”

“…They claimed that the puzzling mismatch between the helioseismic constraints on the solar interior structure and the model can be resolved thanks to this new chemical composition. Moreover, Deshmukh et al (2022) derived a photospheric solar silicon abundance of e = log Si  7.57 0.04. Combining this with meteoritic abundances and photospheric abundances from Caffau et al (2011), they obtained (Z/X) s = 0.0220 ± 0.0020, which is in agreement with the result of Magg et al (2022).…”