Can Recently Derived Solar Photospheric Abundances Be Consistent with Helioseismology?

Abstract

Recent solar abundance analyses (Asplund et al. 2004; Lodders 2003) revise downward the abundances of C, N, O, Ne, and Ar, which reduces the solar photospheric Z/X to 0.017, and Z to ~0.013. Solar models evolved with standard opacities and diffusion treatment using these new abundances give poor agreement with helioseismic inferences for sound speed profile, convection zone helium abundance, and convection zone depth. Here we present helioseismic results for evolved solar models with these reduced photospheric abundances, trying varying diffusion treatments. We compare results for models with no diffusion, enhanced thermal diffusion, and enhanced diffusion of C, N, O, Ne, and Mg only. We find that while each of these models provides some improvements compared to a solar model evolved with the new abundances and standard physics, none restores the good agreement with helioseismology attained using the earlier abundances of, e.g., Grevesse & Sauval (1998). We suggest that opacity increases of about 20% for conditions below the convection zone, or the possibility of accretion of lower-Z material at the surface as the sun arrived at the main sequence, should be investigated to restore agreement. In addition, the new abundance determinations should be re-considered, as, if they are correct, it will be difficult to reconcile solar models with helioseismic results.