Recent solar photospheric abundance analyses ( Asplund et al .
2004 , 2005 ; Lodders 2003 ) revise downward the C , N , O , Ne , and Ar abundances by 0.15 to 0.2 dex compared to previous determinations of Grevesse & Sauval ( 1998 ) .
The abundances of Fe and other elements are reduced by smaller amounts , 0.05 to 0.1 dex .
With these revisions , the photospheric Z/X decreases to 0.0165 ( 0.0177 Lodders ) , and Z to \sim 0.0122 ( 0.0133 Lodders ) .
A number of papers ( e.g. , Basu & Antia 2004a , b ; Montalban et al .
2004 ; Bahcall & Pinsonneault 2004 ; Turck-Chièze et al .
2004a ; Antia & Basu 2005 ) report that solar models evolved with standard opacities and diffusion treatment using these new abundances give poor agreement with helioseismic inferences for sound-speed and density profile , convection-zone helium abundance , and convection-zone depth .
These authors also considered a limited set of models with increased opacities , enhanced diffusion , or abundance variations to improve agreement , finding no entirely satisfactory solution .
Here we explore evolved solar models with varying diffusion treatments , including enhanced diffusion with separate multipliers for helium and other elements , to reduce the photospheric abundances , while keeping the interior abundances about the same as earlier standard models .
While enhanced diffusion improves agreement with some helioseismic constraints compared to a solar model evolved with the new abundances using nominal input physics , the required increases in thermal diffusion rates are unphysically large , and none of the variations tried completely restores the good agreement attained using the earlier abundances .
A combination of modest opacity increases , diffusion enhancements , and abundance increases near the level of the uncertainties , while somewhat contrived , remains the most physically plausible means to restore agreement with helioseismology .
The case for enhanced diffusion would be improved if the inferred convection-zone helium abundance could be reduced ; we recommend reconsidering this derivation in light of new equations of state with modified abundances and other improvements .
We also recommend considering , as a last resort , diluting the convection zone , which contains only 2.5 % of the Sun ’ s mass , by accretion of material depleted in these more volatile elements C , N , O , Ne , & Ar after the Sun arrived on the main sequence .