Solar photosphere

Abstract. We present recent advances in the determination of chemical abundances of galactic Planetary Nebulae and discuss implications resulting from the comparison with theoretical predictions. From the analysis of diagrams of abundances of N/O vs He/H, N/O vs N/H and N/O vs O/H we argue that very likely the often used solar photospheric abundance of oxygen of 8.9, in usual units, is overestimated by a factor of 2-3, as suggested by very recent work in the Sun. This would solve an astrophysical problem with the measured abundances in planetaries. 

Considering the type II-III PNe in Fig. lb coming from the more common less massive progenitors, we have two evident naive interpretations either 1) the initial metallicity of the progenitors was lower than the solar one or 2) the solar photospheric abundance used here has been overestimated. 

Abstract. Coronal abundances have been a subject of debate in the last years due to the availability of high-quality X-ray spectra of many cool stars. Coronal abundance determinations have generally been compared to solar photospheric abundances from this a number of general properties have been inferred, such as the presence of a coronal metal depletion with an inverse First Ionization Potential dependence, with a functional form dependent on the activity level. We report a detailed analysis of the coronal abundance of 4 stars with various levels of activity and with accurately known photospheric abundances. The coronal abundance is determined using a line flux analysis and a full determination of the differential emission measure. We show that, when coronal abundances are compared with real photospheric values for the individual stars, the resulting pattern can be very different some active stars with apparent Metal Abundance Deficiency in the corona have coronal abundances that are actually consistent with their photospheric counterparts. 

The comparison of coronal and photospheric abundances in cool stars is a very important tool in the interpretation of the physics of the corona. Active stars show a very different pattern to that followed by low activity stars such as the Sun, being the First Ionization Potential (FIP) the main variable used to classify the elements. The overall solar corona shows the so-called FIP effect the elements with low FIP (<10 eV, like Ca, N, Mg, Fe or Si), are enhanced by a factor of 4, while elements with higher FIP (S, C, O, N, Ar, Ne) remain at photospheric levels. The physics that yields to this pattern is still a subject of debate. In the case of the active stars (see [2] for a review), the initial results seemed to point towards an opposite trend, the so called Inverse FIP effect , or the MAD effect (for Metal Abundance Depletion). In this case, the elements with low FIP have a substantial depletion when compared to the solar photosphere, while elements with high FIP have same levels (the ratio of Ne and Fe lines of similar temperature of formation in an X-ray spectrum shows very clearly this effect). However, most of the results reported to date lack from their respective photospheric counterparts, raising doubts on how real is the MAD effect. 

By its great mass, the Sun constitutes the major part of the Solar System. In this sense, it is more representative than the planets, which have been the scene of intensive chemical fractionation. The composition of the solar photosphere can thus be compared with the contents of meteorites, stones that fall from the sky, a second source of information on the composition of the protosolar cloud, provided that volatile elements such as hydrogen, helium, carbon, nitrogen, oxygen and neon are excluded. Indeed, the latter cannot be gravitationally bound to such small masses as meteorites and tend to escape into space over the long period since their formation. 

Element Mean Cl chondrites Solar photosphere Solar system abundance ... 

Table 4.1 shows the solar system abundances of the elements as determined by the methods discussed above. For some elements, the photospheric abundances provide the best estimate, whereas for others, the meteorite data must be used. In some cases, the data are equally reliable and an average of the values determined from the solar photosphere and Cl chondrites is used. The abundances of the noble gases come from indirect measurements or theoretical considerations. The method for determining each abundance is indicated in the far right column of Table 4.1. 

What are the advantages and limitations of spectroscopic measurements of the solar photosphere for determining solar system abundances ... 

Cosmochemistry is the study of the chemical compositions of various solar system materials. Chondrites are the most abundant primitive samples. They are essentially sedimentary rocks composed of mechanical mixtures of materials with different origins (chondrules, refractory inclusions, metal, sulfide, matrix), which we will call components. Chondrites formed by the accretion of solid particles within the solar nebula or onto the surfaces of growing planetesimals. They are very old (>4.5 billion years, as measured by radioactive chronometers) and contain some of the earliest formed objects in the solar system. Chondrites have bulk chemical compositions very similar to the solar photosphere, except... 

Dainis Dravins, Luund Observatory, Solar granules the solar photosphere in white light, http //nastol.astro.lu.se/ dainis/HTML/SOLAR.html... 

Relative to silicon, the total elemental lithium is even 140 times less abundantin the solar photosphere than on Earth or inmeteorites, as recorded by the solar spectrum. Since the Li/Si element abundance ratio in the meteorites should also have entered the Sun when it formed, one concludes that the Sun must be destroying its initial lithium supply as it ages. This occurs at the base of the surface convection zone of the Sun. The bottom of that zone lies at a depth that is about 1/4 of the Sun s radius. Here the high temperatures (a few million degrees kelvin, MK) that solar-surface nuclei experience is hot enough to destroy lithium, especially 6Li, by nuclear interactions with protons (6Li + p —3He + 4He). Those proton-induced nuclear reactions destroy 6Li much more readily than they do 7Li because the quantum probabilities of the reaction are greater than for 7Li. As a result, to deplete elemental lithium by a factor of 140 in the Sun... 

K constitutes 93.26% of natural potassium. The elemental K abundance in the solar photosphere and in meteorites are in good agreement 3770 atoms of K per million Si atoms. This isotopic abundance is then... 

The electronic spectrum of the SiH radical was first investigated by Jack-son15) and Rochester16). Subsequently Douglas17), Verma18) and Herzberg et a/.4) extended the analysis of the electronic states. The presence of SiH in the solar photosphere has been firmly established19). 

In the Solar System the bulk elemental composition of the most volatile-rich Cl chondrites resembles closely that of the solar photosphere. Indeed, models that follow the condensation of a solar-composition hot gas reproduce many of the minerals and abundance trends observed in the Solar System. These are also consistent with some of the astronomical observations of dust in protoplanetary disks. Stardust grains also show approximately solar bulk composition in the measurable elements, albeit with some variations (Flynn et al 2006). Some IDPs -mainly the fine-grained, porous, and anhydrous particles - match the solar elemental... 

Element 50% Condensation temperature (K) Earth mantle Mars mantle cv chondrite Solar photosphere... 

Allende Prieto C., Lambert D. L., and Asplund M. (2002) A reappraisal of the solar photospheric C/O ratio. Astrophys. J. 573, L137-L140. 

Is the elemental and isotopic composition of the solar nebula uniform . 03.1.2.2 The composition of the solar photosphere... 

Almost 20 years after Goldschmidt, Suess and Urey (1956) published a new abundance table, which in part relied on solar abundances. In addition, Suess and Urey (1956) introduced arguments based on nucleosynthesis. Their so-called semiempirical abundance rules, primarily the smooth abundance variation of odd-mass nuclei with increasing mass number, were applied to estimate abundances for elements for which analytical data from meteorites were not available or had large errors. The Suess and Urey compilation was very influential for theories of nucleosynthesis and for the development of nuclear astrophysics in general. Later compilations by Cameron (1973), Anders and Grevesse (1989), Palme and Beer (1993), and others took into account improved analytical data on meteorites and the more accurate determination of elemental abundances in the solar photosphere. Over the... 

Table 1 Solar photospheric abundances and meteorite derived solar system abundances (log abundance a(H) = 12).

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