Atmospheric Chemistry in Giant Planets, Brown Dwarfs, and Low-Mass Dwarf Stars III. Iron, Magnesium, and Silicon

We use thermochemical equilibrium calculations to model iron, magnesium, and silicon chemistry in the atmospheres of giant planets, brown dwarfs, extrasolar giant planets (EGPs), and low-mass stars. The behavior of individual Fe-, Mg-, and Si-bearing gases and condensates is determined as a function of temperature, pressure, and metallicity. Our results are thus independent of any particular model atmosphere. The condensation of Fe metal strongly affects iron chemistry by efficiently removing Fe-bearing species from the gas phase. Monatomic Fe is the most abundant Fe-bearing gas throughout the atmospheres of EGPs and L dwarfs and in the deep atmospheres of giant planets and T dwarfs. Mg- and Si-bearing gases are effectively removed from the atmosphere by forsterite (Mg2SiO4) and enstatite (MgSiO3) cloud formation. Monatomic Mg is the dominant magnesium gas throughout the atmospheres of EGPs and L dwarfs and in the deep atmospheres of giant planets and T dwarfs. Silicon monoxide (SiO) is the most abundant Si-bearing gas in the deep atmospheres of brown dwarfs and EGPs, whereas SiH4 is dominant in the deep atmosphere of Jupiter and other gas giant planets. Several other Fe-, Mg-, and Si-bearing gases become increasingly important with decreasing effective temperature. In principle, a number of Fe, Mg, and Si gases are potential tracers of weather or diagnostic of temperature in substellar atmospheres.Comment: 42 pages, 15 figures, submitted to the Astrophysical Journa

The Solar Argon Abundance

The solar argon abundance cannot be directly derived by spectroscopic observations of the solar photosphere. The solar Ar abundance is evaluated from solar wind measurements, nucleosynthetic arguments, observations of B stars, HII regions, planetary nebulae, and noble gas abundances measured in Jupiter's atmosphere. These data lead to a recommended argon abundance of N(Ar) = 91,200(+/-)23,700 (on a scale where Si = 10^6 atoms). The recommended abundance for the solar photosphere (on a scale where log N(H) = 12) is A(Ar)photo = 6.50(+/-)0.10, and taking element settling into account, the solar system (protosolar) abundance is A(Ar)solsys = 6.57(+/-)0.10.Comment: 14 pages, 1 figure, 1 table; submitted to Astrophysical Journa

Boron Abundances in the Galactic Disk

When compared to lithium and beryllium, the absence of boron lines in the optical results in a relatively small data set of boron abundances measured in Galactic stars to date. In this paper we discuss boron abundances published in the literature and focus on the evolution of boron in the Galaxy as measured from pristine boron abundances in cool stars as well as early-type stars in the Galactic disk. The trend of B with Fe obtained from cool F-G dwarfs in the disk is found to have a slope of 0.87 +/- 0.08 (in a log-log plot). This slope is similar to the slope of B with Fe found for the metal poor halo stars and there seems to be a smooth connection between the halo and disk in the chemical evolution of boron. The disk trend of boron with oxygen has a steeper slope of ~1.5. This slope suggests an intermediate behavior between primary and secondary production of boron with respect to oxygen. The slope derived for oxygen is consistent with the slope obtained for Fe provided that [O/Fe] increases as [Fe/H] decreases, as observed in the disk.Comment: 6 pages, 3 figures, IAUS268 Proceeding

Microlunatus parietis sp. nov., isolated from an indoor wall

A Gram-positive, coccoid, non-endospore-forming actinobacterium (strain 12-Be-011T) was isolated from indoor wall material. Based on 16S rRNA gene sequence comparisons, strain 12-Be-011T was clearly shown to belong to the genus Microlunatus and was most closely related to Microlunatus panaciterrae Gsoil 954T (95.7 %), Microlunatus soli CC-12602T (94.9 %), Microlunatus ginsengisoli Gsoil 633T (94.8 %), Microlunatus aurantiacus YIM 45721T (95.5 %) and Microlunatus phosphovorus DSM 10555T (94.7 %). The cell-wall peptidoglycan contained ll-diaminopimelic acid as the diagnostic diamino acid. Mycolic acids were absent. The major menaquinone was MK-9(H4). The polar lipid profile consisted of diphosphatidylglycerol, phosphatidylglycerol, phosphatidylinositol, two unknown phospholipids and one unknown glycolipid. The major fatty acids of iso-C15:0, anteiso-C15:0 and iso-C16:0 supported the affiliation of strain 12-Be-011T to the genus Microlunatus. Physiological and biochemical test results allowed a clear phenotypic differentiation of strain 12-Be-011T from all other species of the genus Microlunatus. Hence, strain 12-Be-011T can be regarded as a representative of a novel species, for which the name Microlunatus parietis sp. nov. is proposed, with the type strain 12-Be-011T (=DSM 22083T=CCM 7636T)

Oldhamite in enstatite achondrites (Aubrites)

Properties of oldhamite (ideally CaS) in aubrites are summarized and compared to oldhamite in enstatite chondrites. The origin of the high REE abundances in aubritic oldhamite and the diversity of REE abundance patterns is addressed. Low CaS/silicate partition coefficients indicate that oldhamite in enstatite achondrites cannot have gained its high REE concentrations during igneous differentiation processes. However, the observed REE abundance patterns in oldhamite can be explained by REE condensation into CaS grains in the solar nebula. The very high melting point of oldhamite plausibly led to its preservation and prevented major exchange reactions of the oldhamite with other aubritic minerals during the short differentiation and metamorphism period on the aubrite parent body. Thus, oldhamite in aubrites is probably a slightly metamorphosed relict condensate, as suggested earlier

Exoplanet Chemistry

The terrestrial and gas-giant planets in our solar system may represent some prototypes for planets around other stars; the exoplanets because most stars have similar overall elemental abundances as our sun. The solar system planets represent at least four chemical planet types, depending on the phases that make them: Terrestrial-like planets made of rock (metal plus silicates), Plutonian planets made of rock and ice, Neptunian giant planets of rocky, icy with low H and He contents, and Jovian gas-giant planets of rocky, icy planets with near-solar H and He contents. The planetary compositions are linked to the chemical fractionation in the planetary accretion disks. Chemical tracers of these fractionations are described. Many known exoplanets are gas-giant planets with up to several Jupiter-masses and their atmospheric chemistry is compared to that of brown dwarfs. Exoplanets in close orbits around their host stars may resemble hot brown dwarfs (L-dwarfs). Planets receiving less radiation form their host may compare more to the methane-rich T dwarfs. The cloud layers resulting from condensation of oxides, metal, sulfides, and salts in these hot and cool gas giant planets and their chemical tracers are described.Comment: 33 pages, 8 figures, 2 tables, in: Formation and Evolution of Exoplanets, R. Barnes (ed.), Wiley, Berlin, in pres