The "Solar Model Problem" Solved by the Abundance of Neon in Stars of the Local Cosmos

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 models has been a triumph of modern astrophysics (Bahcall et al. 2005). However, a recent downward revision by 25-35% of the solar abundances of light elements such as C, N, O and Ne (Asplund et al. 2004) has 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 abundance (Basu Antia 2004, Bahcall et al. 2005). The discrepancies are far beyond the uncertainties in either the data or the model predictions (Bahcall et al. 2005b). Here we report on neon abundances relative to oxygen measured in a sample of nearby solar-like stars from their X-ray spectra. They 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 measurements (Antia Basu 2005, Bahcall et al. 2005c).Comment: 13 pages, 3 Figure

HLA-A and -B alleles and haplotypes in hemochromatosis probands with HFE C282Y homozygosity in central Alabama

BACKGROUND: We wanted to quantify HLA-A and -B allele and haplotype frequencies in Alabama hemochromatosis probands with HFE C282Y homozygosity and controls, and to compare results to those in other populations. METHODS: Alleles were detected using DNA-based typing (probands) and microlymphocytotoxicity (controls). RESULTS: Alleles were determined in 139 probands (1,321 controls) and haplotypes in 118 probands (605 controls). In probands, A*03 positivity was 0.7482 (0.2739 controls; p =< 0.0001; odds ratio (OR) 7.9); positivity for B*07, B*14, and B*56 was also increased. In probands, haplotypes A*03-B*07 and A*03-B*14 were more frequent (p < 0.0001, respectively; OR = 12.3 and 11.1, respectively). The haplotypes A*01-B*60, A*02-B*39, A*02-B*62, A*03-B*13, A*03-B*15, A*03-B*27, A*03-B*35, A*03-B*44, A*03-B*47, and A*03-B*57 were also significantly more frequent in probands. 37.3% of probands were HLA-haploidentical with other proband(s). CONCLUSIONS: A*03 and A*03-B*07 frequencies are increased in Alabama probands, as in other hemochromatosis cohorts. Increased absolute frequencies of A*03-B*35 have been reported only in the present Alabama probands and in hemochromatosis patients in Italy. Increased absolute frequencies of A*01-B*60, A*02-B*39, A*02-B*62, A*03-B*13, A*03-B*15, A*03-B*27, A*03-B*44, A*03-B*47, and A*03-B*57 in hemochromatosis cohorts have not been reported previously

The nature of the heating mechanism for the diffuse solar corona

The temperature of the Sun's outer atmosphere (the corona) exceeds that of the solar surface by about two orders of magnitude, but the nature of the coronal heating mechanisms has long been a mystery(1). The corona is a magnetically dominated environment, consisting of a variety of plasma structures including X-ray bright points, coronal holes and coronal loops. The latter are closed magnetic structures that occur over a range of scales and are anchored at each end in the solar surface. Large-scale regions of diffuse emission are made up of many long coronal loops(2). Here we present X-ray observations of the diffuse corona from which we deduce its likely heating mechanism. We find that the observed variation in temperature along a loop is highly sensitive to the spatial distribution of the heating. From a comparison of the observations and models we conclude that uniform heating gives the best fit to the loop temperature distribution, enabling us to eliminate previously suggested mechanisms of low-lying heating near the footpoints of a loop. Our findings favour turbulent breaking and reconnection of magnetic field lines as the heating mechanism of the diffuse solar corona.</p

A Method to Determine the Heating Mechanisms of the Solar Corona

One of the paradigms about coronal heating has been the belief that the mean or summit temperature of a coronal loop is completely insensitive to the nature of the heating mechanisms. However, we point out that the temperature profile along a coronal loop is highly sensitive to the form of the heating. For example, when a steady state heating is balanced by thermal conduction, a uniform heating function makes the heat flux a linear function of distance along the loop, while T-7/2 increases quadratically from the coronal footpoints; when the heating is concentrated near the coronal base, the heat flux is small and the T-7/2 profile is flat above the base; when the heat is focused near the summit of a loop, the heat flux is constant and T-7/2 is a linear function of distance below the summit. It is therefore important to determine how the heat deposition from particular heating mechanisms varies spatially within coronal structures such as loops or arcades and to compare it to high-quality measurements of the temperature profiles.We propose a new two-part approach to try and solve the coronal heating problem, namely, first of all to use observed temperature profiles to deduce the form of the heating, and second to use that heating form to deduce the likely heating mechanism. In particular, we apply this philosophy to a preliminary analysis of Yohkoh observations of the large-scale solar corona. This gives strong evidence against heating concentrated near the loop base for such loops and suggests that heating uniformly distributed along the loop is slightly more likely than heating concentrated at the summit. The implication is that large-scale loops are heated in situ throughout their length, rather than being a steady response to low-lying heating near their feet or at their summits. Unless waves can be shown to produce a heating close enough to uniform, the evidence is therefore at present for these large loops more in favor of turbulent reconnection at many small randomly distributed current sheets, which is likely to be able to do so. In addition, we suggest that the decline in coronal intensity by a factor of 100 from solar maximum to solar minimum is a natural consequence of the observed ratio of magnetic field strength in active regions and the quiet Sun; the altitude of the maximum temperature in coronal holes may represent the dissipation height of Alfven waves by turbulent phase mixing; and the difference in maximum temperature in closed and open regimes may be understood in terms of the roles of the conductive flux there.</p