Shallow mixing in the solar photosphere inferred from revised beryllium abundances

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Abstract

The chemical compositions of the Sun and meteorites are the benchmarks against which the abundances of elements in all other astronomical objects are compared.A long-standing problem [1] has been the abundance of lithium in the Sun's photosphere, which is [approximately] 140 times less than the meteoritic value (which represents the lithium abundance at the time the Solar System formed). This depletion requires that material from the photosphere be transported below the convective zone into regions where the temperature is high enough that nuclear processing can remove lithium. The models [2,3] best able to do so simultaneously deplete beryllium by about a factor of two, which is consistent with previous measurements [4,5] of the beryllium abundance in the solar photosphere. But here we show that these previous measurements are in error, because they did not fully account for the continuous opacity in the ultraviolet region of the spectrum where the beryllium lines are observed. We find that, after correcting for this opacity, solar beryllium is not depleted at all with respect to the meteoritic value. This implies that mixing in the solar photosphere is more superficial than had hitherto been supposed, consistent with the shallow mixing inferred from recent helioseismic data [6].

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