Lyα Flux Impact from the Parent Star on Hα Absorption in the Atmospheres of the Hot Jupiters HD189733b and HD 209458b

Astronomy Reports - Simulation results are presented for the Lyα flux impact from the parent star on the Hα absorption spectrum in the atmospheres of the hot Jupiters HD189733b and HD...     

Oxygen isotope exchange and disequilibrium between calcite and tremolite in the absence and presence of an experimental C–O–H fluid

Oxygen isotope exchange between minerals during metamorphism can occur in either the presence or the absence of aqueous fluids. Oxygen isotope partitioning among minerals and fluid is governed by both chemical and isotopic equilibria during these processes, which progress by intragranular and intergranular diffusion as well as by surface reactions. We have carried out isotope exchange experiments in two- and three-phase systems, respectively, between calcite and tremolite at high temperatures and pressures. The two-phase system experiments were conducted without fluid either at 1 GPa and 680 °C for 7 days or at 500 MPa and 560 °C for 20 days. Extrapolated equilibrium fractionations between calcite and tremolite are significantly lower than existing empirical estimates and experimental determinations in the presence of small amounts of fluid, but closely match calculated fractionations by means of the increment method for framework oxygen in tremolite. The small fractionations measured in the direct calcite–tremolite exchange experiments are interpreted by different rates of oxygen isotope exchange between hydroxyl oxygen, framework oxygen and calcite during the solid–solid reactions where significant recrystallization occurs. The three-phase system experiments were accomplished in the presence of a large amount of fluid (CO₂+H₂O) at 500 MPa and 560 °C under conditions of phase equilibrium for 5, 10, 20, 40, 80, 120, 160, and 200 days. The results show that oxygen isotope exchange between minerals and fluid proceeds in two stages: first, through a mechanism of dissolution-recrystallization and very rapidly; second, through a mechanism of diffusion and very slowly. Synthetic calcite shows a greater rate of isotopic exchange with fluid than natural calcite in the first stage. The rate of oxygen diffusion in calcite is approximately equal to or slightly greater than that in tremolite in the second stage. A calculation using available diffusion coefficients for calcite suggests that grain boundary diffusion, rather than volume diffusion, has been the dominant mechanism of oxygen transport between the fluid and the mineral grains in the later stage.Editorial responsibility: T.L. Grove     

Behavior of the broad Hα component in the Seyfert galaxy NGC 4151 in 1976–2003

Variations in the flux and profile of the broad Hα component in the Seyfert galaxy NGC 4151 are analyzed based on spectral observations acquired from 1976 to spring 2003. The procedure used to distinguish components is described. There is a strong correlation between the flux of the broad Hα component and the U flux of the galactic nucleus. There was an appreciable increase in the intensity of the broad Hα in 1990–2000, with the flux reaching a maximum in 1996. The intensity and shape of an emission feature that appeared in the red wing of the broad Hα component at the end of 2002 are estimated.     

Filaments and the underlying surface from He I and H<Emphasis Type="Italic">α</Emphasis> line observations

Bright bands are observed along filaments in the He I 1083 nm line, while both bright and dark bands are observed along Hα 656.3 nm filaments. The range of brightness variations near He I filaments is 1.005–1.10 times the unperturbed brightness, with an average of 1.031 ± 0.01, while this range is 0.91–1.5 times the unperturbed brightness for Hα filaments. The physical state of the matter in these bands is investigated. Computations of the band brightness have been carried out for various chromospheric models, aimed at explaining the observed features of the bands. Two types of models are considered: with temperature or density variations in the upper chromosphere, and with temperature variations in the middle and lower chromosphere. In the first type of model, the brightness in the He I line is changed, but the Hα brightness is not. In the second type of model, only the Hα brightness is changed. Using the variations of the chromospheric parameters and both types of models, we obtained various combinations of band brightnesses in the He I line and in Hα. The brightnesses of regions were estimated by calculating the profiles of the He I and Hα lines in the corresponding models in a non-LTE approximation. A comparison of the observed and calculated quantities indicates that the enhancement in the brightness in the He I line is due to a decrease in temperature or density in the upper chromosphere (where the temperatures are about 10 000–24 000 K). The enhancement and dimming of the brightness in Hα are due to an increase or decrease of the temperature in the middle and lower chromosphere (where the temperatures are 6000–9000 K) by 800–1000 K. The dependence of the band brightness on distance from the center of the solar disk is also considered. The brightness in the He I line increases from the center to the limb by 2–4%. Computations of the center–limb brightness variaions correspond to the observed results.     

“Blind passes” and the production of green security through violence on the Guatemalan border

Guatemalan protected areas have been sites for genocidal massacres, drug trafficking landing strips, and remilitarized “states of emergency,” but these activities are rarely considered in relation to conservation practices. This paper employs a political ecology approach to analyze interpellations of transboundary spaces as security threats, arguing that threat narratives produce insecurity in conservation spaces. Instead of assuming the primacy of neoliberalism in producing protected areas as sites of violence in the service of capitalism, the analysis traces the changing meanings of security in relation to Guatemala’s borderlands, from Cold War National Security Doctrine to discourses of citizen security in the twenty-first century Drug War. It is in the unmanned “blind passes” (pasos ciegos) of the Guatemalan–Mexican border, rendered as insecure spaces through the state’s putative absence, that policing paradoxically seeks to ensure “citizen security” through violence.     

The deformation of porous sandstones; are Byerlee friction and the critical state line equivalent?

Certain rock properties that depend on intergranular fracture and frictional sliding appear to be independent of rock type. This relationship is true for the rock-on-rock frictional sliding coefficient. The generalization has been widely applied to geomechanical modelling of upper crustal strength. Porous sandstones can be relatively weak and poorly cohesive, hence susceptible to deformation involving grain fragmentation and pore collapse. The critical state theory is commonly applied to describe such behaviour. Previous work showed that the yield surface is substantially independent of rock type when mean stress and differential stress are normalized by the grain crushing pressure, implying that the critical state line is rock type-independent and equivalent to the frictional sliding criterion. We test these hypotheses using previously published data for a range of porous sandstones augmented by new experimental results on Hollington and Berea sandstones deformed to large strains to define the critical state line over a wide range of pressures for each rock type. Results confirm the rock type-independence of the critical state line and show that it is nearly equivalent to frictional sliding. These relationships point to a simple procedure for estimating approximately the mechanical properties of sandstones based only on petrographic characteristics.     

A contribution to the crystal chemistry of the voltaite group: solid solutions, Mössbauer and infrared spectra, and anomalous anisotropy

Voltaite is a mineral of fumaroles, solfatares, coal-fire gas vents, and acid-mine drainage systems. The nominal composition is K₂Fe₅ ²⁺Fe₃ ³⁺Al(SO₄)₁₂·18H₂O and the nominal symmetry is cubic, $Fd\overline{3}c$ . The tetragonal (I4₁/acd) superstructure of voltaite is known as the mineral pertlikite. In this study, we investigated 22 synthetic voltaite samples in which Fe²⁺ was partially or completely replaced by Mg, Zn, Mn, or Cd, by single-crystal and powder X-ray diffraction (both in-house and synchrotron). Two samples contained NH₄ ⁺ instead of K⁺. The structure of voltaite is based on a framework defined by kröhnkite-like heteropolyhedral chains which host both M³⁺ and M²⁺ in octahedral coordination. Unit cell dimensions of the end-members scale almost linearly with the size of M²⁺. In the Fe²⁺-Mg-Zn solid solutions, the Fe²⁺-Mg and Fe²⁺-Zn solutions are linear (ideal) in terms of their lattice-parameter variations. The Mg-Zn solid solution, however, is strongly non-ideal. A detailed analysis of the topology of the chains showed that this behavior originates in expansion and contraction of individual M²⁺-O bonds within the chains. In the Mg-Zn solid solution, some of the M²⁺-O bonds expand while none contract. In the other solid solutions, expansion of some M²⁺-O bonds is always compensated by contraction of the other ones. Parts of the nominally cubic crystals are optically anisotropic and their symmetry is found to be tetragonal by single crystal X-ray diffraction measurements. The coexistence of cubic and tetragonal sectors within a single crystal without any detectable difference in their chemical composition is difficult to explain in terms of growth of such composite crystals. Mössbauer and infrared spectra collected on our synthetic crystals conform with previously published data.     

Mesozoic paleogeography and paleoclimates – A discussion of the diverse greenhouse and hothouse conditions of an alien world

The Mesozoic was the time of the break-up of Pangaea, with profound consequences not only for the paleocontinental configuration, but also for paleoclimates and for the evolution of life. Cool greenhouse conditions alternated with warm greenhouse and even hothouse conditions, with global average temperatures around 6–9 °C warmer than the present ones. There are only sparse and controversial evidence for polar ice; meanwhile, extensive evaporitic and desertic deposits are well described. Global sea levels were mainly high, and the content of atmospheric O₂ was varying between 15 and 25%. These conditions make the Mesozoic Earth an alien world compared to present-day conditions. Degassing from volcanism linked to the rifting process of Pangaea and methane emissions from reptilian biotas were climate-controlling factors because they enhanced atmospheric CO₂ concentrations up to 16 times compared to present-day levels. The continental break-up modified paleopositions and shoreline configurations of the landmasses, generating huge epicontinental seas and altering profoundly the oceanic circulation. The Mesozoic was also a time of important impact events as probable triggers for “impact winters”; and for the Era at least nine huge (diameter > 20 km) impact structures are known. This paper presents an abridged but updated overview of the Mesozoic paleogeographic and paleoclimatic variations, characterizing each period and sub-period in terms of paleoclimatic state and main tectonic and climatic events, and provides a brief geologic, stratigraphic, paleoclimatic and taphonomic characterization of dinosaur occurrences as recorded in the Brazilian continental basins.     

Age and isotopic evidence for the origin of the Archæan granitoid intrusives of the Johannesburg Dome,South Africa

Results of RbSr, PbPb and SmNd whole rock, Rbr biotite and PbPb zircon evaporation analyses are presented for certain granitoid rocks from the Johannesburg Dome. These data indicate that the granodiorite, granite and leucosome from migmatite were emplaced ∼ 3090 Ma ago, were genetically related and were derived primarily from a source between ∼ 3300 and ∼ 3500 Ma old. A portion of the granodiorite and granite might have been derived from a source between ∼ 4000 and ∼ 4300 Ma old. The tonalite was emplaced ∼ 3170 Ma ago and was derived from a source between 3.3 and 3.5 Ga old. RbSr biotite-whole rock ages, ranging between about ∼ 2614 and ∼ 2080 Ma, probably reflect complete resetting during differential uplift, erosion and cooling of the granitoid rocks in the Neoarchæan and Palæoproterozoic. If so, they apparently were not influenced by the emplacement of the ∼ 2060 Ma Bushveld Igneous Complex or the ∼ 2000 Ma Vredefort event. The granodiorite, granite and leucosome were emplaced coeval with and may be genetically related to compositionally similar plutonic and volcanic rocks in the Barberton area, Vredefort structure and Dominion Group.     

Solar flare-related eruptions followed by long-lasting occultation of the emission in the He II 304 ? line and in microwaves

Plasma with a temperature close to the chromospheric one is ejected in solar eruptions. Such plasma can occult some part of emission of compact sources in active regions as well as quiet solar areas. Absorption phenomena can be observed in the microwave range as the so-called “negative bursts” and also in the He II 304 ? line. The paper considers three eruptive events associated with rather powerful flares. Parameters of absorbing material of an eruption are estimated from multi-frequency records of a “negative burst” in one event. “Destruction” of an eruptive filament and its dispersion like a cloud over a huge area observed as a giant depression of the 304 ? line emission has been revealed in a few events. One of the three currently known events is considered in this paper. One more of the events considered here is a possible candidate for such events.     

Multicolor photoelectric WBVR observations of the close binary system HZ Her = Her X-1 in 1986–1988. Method and observations

We present results of four-color (WBVR) photoelectric observations of the close binary HZ Her = Her X-1 in 1986–1988. As a rule, the duration of the observations exceeded two 35-day X-ray orbital periods in the 1986–1988 observing seasons. The accuracy and length of the photoelectric observations facilitated multi-faceted studies, which enabled us to define several fine photometric effects in the light curves of the binary more precisely and attempt to interpret them in a model for the matter flow from the optical component to the accretion disk around the neutron star. This model provides a satisfactory explanation for the inhomogeneity of the gas flow and “hot spot,” as well as the existence of distinct “splashes” moving in their own Keplerian orbits around the outer parts of the Keplerian disk. We present series of light curves for all the observing seasons, as well as color-color diagrams that reflect the physics of various photometric effects. The transformation coefficients for each of the instrumental systems for the three observatories at which the observations were carried out are given. Atmospheric extinction was taken into account duringmulti-color observations of the object, with subsequent correction for atmospheric effects with accuracies ranging from 0.003 ^m to 0.005 ^m for air masses up to M(z) = 2.     

Wavelength-dispersive x-ray fluorescence spectrometric determination of tantalum in columbite-tantalite using TaKα and an LiF 420 analysing crystal

The paper proposes a simple, accurate, precise, and rapid method for determining the high atomic number (Z) major-element, tantalum (Z = 73), in the rare mineral, columbite [(Fe,Mn) (Nb,Ta)₂O₆] — tantalite [(Fe,Mn) (Ta,Nb)₂O₆], by wavelength-dispersive x-ray fluorescence spectrometry (WDXRFS). The other major-element in columbite-tantalite is the lower atomic number niobium (Z = 41). The method uses the characteristic radiation, TaKα, and an LiF 420 analysing crystal, to overcome the problems associated with the serious x-ray spectral-line interference of the secondorder NbKα and NbKβ with the first-order TaLα1 and TaLβ1 respectively.     

Pulkovo catalog of relative positions and motions of visual double and multiple stars from photographic observations with the 26-inch refractor in 1960–2007

The results of long-term, uniform, photographic observations of visual double and multiple stars obtained on the Pulkovo 26″ refractor are presented. Relative positions are calculated for 259 pairs of visual double stars in 194 systems, with the relative motions also computed for 127 pairs. Lower limits for the total masses of the systems for which elliptical orbits possible are also found for 48 pairs with reliable parallaxes from the Hipparcos catalog. The accuracies of the three measuring machines used in the reduction of the photographic plates are compared. Component separations measured with different machines can differ by as much as 0.2″, demonstrating the advantages of using uniform observations.     

Becoming a young migrant or stayer seen through the lens of ‘householding’: Households ‘in flux’ and the intersection of relations of gender and seniority

This paper conceptualises migration and staying by young rural Lao in the empirical context of above replacement level fertility as manifestations of ‘householding’ that interacts with other dimensions of householding. Drawing on the framework of the inter-generational contract and by juxtaposing qualitative and quantitative data I show that becoming a young migrant and becoming or remaining a young stayer is shaped by young migrants’ situated agency.The second part of the paper departs from conventional household-based analyses and introduces the notion of ‘households in flux’. This highlights the dynamic interaction between changing external dynamics affecting rural households, and internal dynamics that constantly reconfigure the field of the household. These conceptual readjustments require going beyond inflexible notions of the household, the analytical disconnection between a focus on migrants and stayers in migration research, and static readings of relations of gender and generation. Furthermore, the paper argues that intra-household relations need to be appreciated as gendered relations of relative seniority which are in the process of householding constantly made and remade, among other things, by young dependents through ‘staying’ and ‘leaving’. These conceptual moves help explain the empirical puzzle of why in rural Lao households young women are both the ones most inclined to become a young migrant as well as most inclined to become or remain a young stayer.