The ‘solar model problem’ solved by the abundance of neon in nearby stars

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Abstract

The interior structure of the Sun can be studied with great accuracy using observations of its oscillations, similar to seismology of the Earth. Precise agreement between helioseismological measurements and predictions of theoretical solar models1 has been a triumph of modern astrophysics. A recent downward revision by 25–35 per cent of the solar abundances of light elements such as C, N, O and Ne (ref. 2) has, however, broken this accordance: models adopting the new abundances incorrectly predict the depth of the convection zone, the depth profiles of sound speed and density, and the helium abundance1,3. The discrepancies are far beyond the uncertainties in either the data or the model predictions4. Here we report neon-to-oxygen ratios measured in a sample of nearby solar-like stars, using their X-ray spectra. The abundance ratios are all very similar and substantially larger than the recently revised solar value. The neon abundance in the Sun is quite poorly determined. If the Ne/O abundance in these stars is adopted for the Sun, the models are brought back into agreement with helioseismology measurements5,6.

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Figure 1: A Chandra Medium Energy Grating X-ray spectrum of the M1 V star AU Mic.
Figure 2: Derived Ne/O abundance ratios by number, ANe/AO, versus the coronal activity index LX/Lbol.
Figure 3: The temperature-insensitive O/Ne emissivity ratio.

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Acknowledgements

We thank G. Share, R. Murphy, W. Ball and D. Garcia-Alvarez for discussions and comments. J.J.D. was supported by a NASA contract to the Chandra X-ray Center. P.T. was supported by a Chandra award issued by the Chandra X-ray Center, which is operated by SAO for and on behalf of NASA. J.J.D. thanks the NASA AISRP for providing financial assistance for the development of the PINTofALE package.

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Correspondence to Jeremy J. Drake.

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Supplementary Data

A document containing a more complete list of some existing measurements of the Ne/O abundance ratio in the solar outer atmosphere, together with citations to the original sources. (PDF 21 kb)

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Drake, J., Testa, P. The ‘solar model problem’ solved by the abundance of neon in nearby stars. Nature 436, 525–528 (2005) doi:10.1038/nature03803

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