Neon Lights up a Controversy: The Solar Ne/O Abundance

Abstract

The standard solar model was so reliable that it could predict the existence of the massive neutrino. Helioseismology measurements were so precise that they could determine the depth of the convection zone. This agreement between theory and observation was the envy of all astrophysics -until recently when sophisticated three-dimensional hydrodynamic calculations of the solar atmosphere reduced the metal content by a factor of almost two. Antia & Basu (2005) suggested that a higher value of the solar neon abundance, A N e /A O = 0.52, would resolve this controversy. Drake & Testa (2005) presented strong evidence in favor of this idea from a sample of 21 Chandra stars with enhanced values of the neon abundance, A N e /A O = 0.41. In this paper, we have analyzed solar active region spectra from the archive of the Flat Crystal Spectrometer on Solar Maximum Mission, a NASA mission from the 1980s, as well as full-Sun spectra from the pioneering days of X-ray astronomy in the 1960s. These data seem consistent with the standard neon-to-oxygen abundance value, A N e /A O = 0.15 (Grevesse & Sauval 1998). If these results prove to be correct, than the enhanced-neon hypothesis will not resolve the current controversy.

No first ionization potential fractionation in the active stars AR Piscium and AY Ceti

“…These results confirm those of λ And and V851 Cen (Sanz-Forcada et al 2004), displayed here for easier comparison (Fig. 7 "solar model problem" (see also discussion in Schmelz et al 2005). The ratios in the coronae of AR Psc and AY Cet are consistent with the value observed by Drake & Testa (2005).…”

Extinction Columns and Intrinsic X‐Ray Spectra of the Anomalous X‐Ray Pulsars

“…Briefly, Asplund et al (2005) inferred from improved models for the solar atmosphere that the solar oxygen and carbon abundances were much lower than thought previously. The revised abundances, however, led to discrepancies between helioseismology and models for the solar interior (e.g., Schmelz et al 2005). To remedy this, it has been suggested that the abundance of neon might have to be revised upwards (e.g., Bahcall et al 2005), but this leads to a number of other problems (e.g., Young 2005;Drake & Testa 2005).…”

Determining Solar Abundances Using Helioseismology

“…This solution seemed to be particularly promising, since Drake & Testa (2005) found that most neighboring stars seem to have a much higher Ne/O ratio than the Sun. However, Schmelz et al (2005) and Young (2005) reanalyzed solar X-ray and UV data, respectively, to find that the Ne/O ratio of the Sun is indeed consistent with the old lower value. Interestingly, recent measurements by Ayres et al (2006), using the CO lines from a combination of data from the shuttle-borne Atmospheric Trace Molecule Spectroscopy (ATMOS) Fourier transform spectrometer and groundbased observations yields an oxygen abundance that is much higher than the recent ASP value and close to that of GS.…”