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

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

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

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

Brevibacterium sandarakinum sp. nov., isolated from a wall of an indoor environment

A Gram-stain-positive, rod-shaped, non-endospore-forming, orange-pigmented (coloured) actinobacterium (01-Je-003T) was isolated from the wall of an indoor environment primarily colonized with moulds. On the basis of 16S rRNA gene sequence similarity studies, strain 01-Je-003T was shown to belong to the genus Brevibacterium and was most similar to the type strains of Brevibacterium picturae (98.8% similarity), Brevibacterium marinum (97.3%) and Brevibacterium aurantiacum (97.2 %). Chemotaxonomic data [predominant quinone menaquinone MK-8(H2); polar lipid profile consisting of major compounds diphosphatidylglycerol, phosphatidylglycerol and an unidentified glycolipid; characteristic cell-wall diamino acid meso-diaminopimelic acid; polyamine pattern showing major compounds putrescine and cadaverine; major fatty acids anteiso-C15:0 and anteiso-C17:0] supported the affiliation of strain 01-Je-003T to the genus Brevibacterium. The results of DNA–DNA hybridizations and physiological and biochemical tests allowed genotypic and phenotypic differentiation of strain 01-Je-003T from the two most closely related species, B. picturae and B. marinum. Strain 01-Je-003T therefore represents a novel species, for which the name Brevibacterium sandarakinum sp. nov. is proposed, with the type strain 01-Je-003T (5DSM 22082T 5CCM 7649T)

[TiII] and [NiII] emission from the strontium filament of eta Carinae

We study the nature of the [TiII] and [NiII] emission from the so-called strontium filament found in the ejecta of eta Carinae. To this purpose we employ multilevel models of the TiII and NiII systems which are used to investigate the physical condition of the filament and the excitation mechanisms of the observed lines. For the TiII ion, for which no atomic data was previously available, we carry out ab initio calculations of radiative transition rates and electron impact excitation rate coefficients. It is found that the observed spectrum is consistent with the lines being excited in a mostly neutral region with an electron density of the order of $10^7$ cm$^{-3}$ and a temperature around 6000 K. In analyzing three observations with different slit orientations recorded between March~2000 and November~2001 we find line ratios that change among various observations, in a way consistent with changes of up to an order of magnitude in the strength of the continuum radiation field. These changes result from different samplings of the extended filament, due to the different slit orientations used for each observation, and yield clues on the spatial extent and optical depth of the filament. The observed emission indicates a large Ti/Ni abundance ratio relative to solar abundances. It is suggested that the observed high Ti/Ni ratio in gas is caused by dust-gas fractionation processes and does not reflect the absolute Ti/Ni ratio in the ejecta of \etacar. We study the condensation chemistry of Ti, Ni and Fe within the filament and suggest that the observed gas phase overabundance of TiComment: 14 paginas, 12 figure

Parent Stars of Extrasolar Planets. XI. Trends with Condensation Temperature Revisited

We report the results of abundance analyses of new samples of stars with planets and stars without detected planets. We employ these data to compare abundance-condensation temperature trends in both samples. We find that stars with planets have more negative trends. In addition, the more metal-rich stars with planets display the most negative trends. These results confirm and extend the findings of Ramirez et al. (2009) and Melendez et al. (2009), who restricted their studies to solar analogs. We also show that the differences between the solar photospheric and CI meteoritic abundances correlate with condensation temperature.Comment: 7 pages, 11 figures; to be published in MNRA