ISO Observations of Symbiotic Stars

A number of symbiotic stars have been observed with ISO. In addition to a number of emission lines, SWS observations of the symbiotic novae RR Tel and V1016 Cyg reveal prominent, broad 10 & 18 μm silicate dust features. The 10 μm features are similar to the crystalline silicate profiles seen in classical novae. There is some evidence that the silicate brightness in V1016 Cyg varies with Mira-component phase. However, the silicate feature in RR Tel also showed some variation even though observations were made at very similar Mira-component phases. PHT observations of S-type symbiotic stars show the IR emission to be dominated by the red-giant component. However, an excess in the PHT-P filters from 10 to 15 μm is evident in all the stars, and there may be a broad 3.2 μm absorption feature or a broad 3.8 μm emission feature. At this time we have no adequate physical explanations for any of these features. This revised version was published online in August 2006 with corrections to the Cover Date.     

Distant field blue horizontal branch stars – III. Identification of a probable outer halo stream at Galactocentric distance r= 70 kpc

We present FOcal Reducer/low dispersion Spectrograph-1 spectra (from the European Southern Observatory's Very Large Telescope) of a sample of 34 faint  20.0 < g * < 21.1  A-type stars selected from the Sloan Digital Sky Survey Early Data Release, with the goal of measuring the velocity dispersion of blue horizontal branch (BHB) stars in the remote Galactic halo,   R ∼ 80 kpc  . We show that colour selection with  1.08 < u *− g * < 1.40  and  −0.2 < g *− r * < −0.04  minimizes contamination of the sample by less luminous blue stragglers. In classifying the stars we confine our attention to the 20 stars with spectra of signal-to-noise ratio >15 Å⁻¹. Classification produces a sample of eight BHB stars at distances  65–102 kpc  from the Sun (mean 80 kpc), which represents the most distant sample of Galactic stars with measured radial velocities. The dispersion of the measured radial component of the velocity with respect to the centre of the Galaxy is  58 ± 15 km s⁻¹  . This value is anomalously low in comparison with measured values for stars at smaller distances, as well as for satellites at similar distances. Seeking an explanation for the low measured velocity dispersion, further analysis reveals that six of the eight remote BHB stars are plausibly associated with a single orbit. Three previously known outer halo carbon stars also appear to belong to this stream. The velocity dispersion of all nine stars relative to the orbit is only  15 ± 4 km s⁻¹  . Further observations along the orbit are required to trace the full extent of this structure on the sky.     

The electrical structure of the Slave craton

The Slave craton in northwestern Canada, a relatively small Archean craton (600×400 km), is ideal as a natural laboratory for investigating the formation and evolution of Mesoarchean and Neoarchean sub-continental lithospheric mantle (SCLM). Excellent outcrop and the discovery of economic diamondiferous kimberlite pipes in the centre of the craton during the early 1990s have led to an unparalleled amount of geoscientific information becoming available.

Over the last 5 years deep-probing electromagnetic surveys were conducted on the Slave, using the natural-source magnetotelluric (MT) technique, as part of a variety of programs to study the craton and determine its regional-scale electrical structure. Two of the four types of surveys involved novel MT data acquisition; one through frozen lakes along ice roads during winter, and the second using ocean-bottom MT instrumentation deployed from float planes.

The primary initial objective of the MT surveys was to determine the geometry of the topography of the lithosphere–asthenosphere boundary (LAB) across the Slave craton. However, the MT responses revealed, completely serendipitously, a remarkable anomaly in electrical conductivity in the SCLM of the central Slave craton. This Central Slave Mantle Conductor (CSMC) anomaly is modelled as a localized region of low resistivity (10–15 Ω m) beginning at depths of 80–120 km and striking NE–SW. Where precisely located, it is spatially coincident with the Eocene-aged kimberlite field in the central part of the craton (the so-called “Corridor of Hope”), and also with a geochemically defined ultra-depleted harzburgitic layer interpreted as oceanic or arc-related lithosphere emplaced during early tectonism. The CSMC lies wholly within the NE–SW striking central zone defined by Grütter et al. [Grütter, H.S., Apter, D.B., Kong, J., 1999. Crust–mantle coupling; evidence from mantle-derived xenocrystic garnets. Contributed paper at: The 7th International Kimberlite Conference Proceeding, J.B. Dawson Volume, 1, 307–313] on the basis of garnet geochemistry (G10 vs. G9) populations.

Deep-probing MT data from the lake bottom instruments infer that the conductor has a total depth-integrated conductivity (conductance) of the order of 2000 Siemens, which, given an internal resistivity of 10–15 Ω m, implies a thickness of 20–30 km. Below the CSMC the electrical resistivity of the lithosphere increases by a factor of 3–5 to values of around 50 Ω m. This change occurs at depths consistent with the graphite–diamond transition, which is taken as consistent with a carbon interpretation for the CSMC.

Preliminary three-dimensional MT modelling supports the NE–SW striking geometry for the conductor, and also suggests a NW dip. This geometry is taken as implying that the tectonic processes that emplaced this geophysical–geochemical body are likely related to the subduction of a craton of unknown provenance from the SE (present-day coordinates) during 2630–2620 Ma. It suggests that the lithospheric stacking model of Helmstaedt and Schulze [Helmstaedt, H.H., Schulze, D.J., 1989. Southern African kimberlites and their mantle sample: implications for Archean tectonics and lithosphere evolution. In Ross, J. (Ed.), Kimberlites and Related Rocks, Vol. 1: Their Composition, Occurrence, Origin, and Emplacement. Geological Society of Australia Special Publication, vol. 14, 358–368] is likely correct for the formation of the Slave's current SCLM.     

采用SilviScan-3TM研究木材性质的方法及其在气候变化研究中的应用

系统介绍了利用SilviScan-3TM测量细胞结构、木材密度、微纤丝角和划分年轮界线的方法,并以祁连山青海云杉为例,分析青海云杉6个木材性质参数(年轮细胞直径、年轮细胞壁厚、年轮宽度、年轮密度、年轮微纤丝角、年轮弹性模量)与气候因子的关系,以期为利用多个树轮参数研究气候提供参考。结果表明:6个木材性质参数与月平均气温和月降水量都有显著相关的月份,但显著相关的时间段不同,并且微纤丝角和细胞结构参数中包含的气候信息强于常用的年轮宽度和年轮密度。SilviScan-3TM测量木材性质参数的优越性体现在:测量精度高、速度快,能在同一个试样上测量多个参数并能精确定年。     

Micromorphological characteristics of glacimarine sediments: implications for distinguishing genetic processes of massive diamicts

Glacimarine diamicts are produced by diverse processes, and genetic differentiation is often problematic using macro-sedimentological criteria alone. Micromorphology offers a potentially helpful tool in such investigations. Macroscopically massive diamict samples of known glacimarine origin, from the Polar North Atlantic, Antarctica and north Irish Sea, were prepared for micromorphological analysis to (1) identify microstructures unique to different modes of sedimentation and (2) interpret genetic processes from those structures. The samples comprised examples of debris-flow, iceberg-turbate and suspension settling deposits from late Quaternary glacier-influenced marine environments: tidewater glacier, sub- or pro-ice shelf and continental slopes in front of ice stream termini. Results show two significant features of debris-flow sediments: a bimodal grain fabric of near-horizontal and -vertical grains, and laminated clay and silt coatings on sand and pebble grains. Coatings are best developed in sediments with finer grain-size distributions and in debris-flow sediments which have had relatively long run-out distances on trough-mouth fans, suggesting continuous rotation of grains in a buoyant, turbulent aqueous environment. This is significant because it precludes debris-flow delivery by plug flow. The micromorphology of iceberg turbate has not been described previously. It contains structures similar to those described in tills, so that unambiguous identification of these sediments seems unlikely based on micromorphological criteria alone. Suspension sediments range from fine-grained massive diamicts containing microfossils to more heterogeneous coarser sediments characterised by abrupt textural variations, from ice-distal and ice-proximal glacimarine environments respectively. The ice-proximal sediments contain fine vertical lineations marking the trajectories of dropstones through wet matrix. These dropstone tracks have not been reported in previous studies.     

Note on the age and fauna of the Lynton Beds (Lower Devonian) of north Devon

The Lynton Beds represent shallow marine sediments with a restricted fauna dominated by brachiopods. The age indicated by the brachiopod fauna is late Emsian, although the possibility of a younger date for the uppermost horizons cannot be discounted.     

Planetary orbital equations in externally-perturbed systems: position and velocity-dependent forces

The increasing number and variety of extrasolar planets illustrates the importance of characterizing planetary perturbations. Planetary orbits are typically described by physically intuitive orbital elements. Here, we explicitly express the equations of motion of the unaveraged perturbed two-body problem in terms of planetary orbital elements by using a generalized form of Gauss’ equations. We consider a varied set of position and velocity-dependent perturbations, and also derive relevant specific cases of the equations: when they are averaged over fast variables (the “adiabatic” approximation), and in the prograde and retrograde planar cases. In each instance, we delineate the properties of the equations. As brief demonstrations of potential applications, we consider the effect of Galactic tides. We measure the effect on the widest-known exoplanet orbit, Sedna-like objects, and distant scattered disk objects, particularly with regard to where the adiabatic approximation breaks down. The Mathematica code which can help derive the equations of motion for a user-defined perturbation is freely available upon request.     

A method for calculating effective bulk composition modification due to crystal fractionation in garnet-bearing schist: implications for isopleth thermobarometry

Quantitative P–T path determination in metamorphic rocks is commonly based on the variation in composition of growth‐zoned garnet. However, some component of growth zoning in garnet is necessarily the result of an effective bulk composition change within the rock that has been generated by crystal fractionation of components into the core of garnet. Therefore, any quantitative calculation of the P–T regime of garnet growth should be completed using an accurate assessment of the composition of the chemical system from which garnet is growing. Consequently, a method for calculating the extent of crystal fractionation that provides a means of estimating the composition of the unfractionated rock at any stage during garnet growth is developed. The method presented here applies a Rayleigh fractionation model based on measured Mn content of garnet to generate composition v. modal proportion curves for garnet, and uses those curves to estimate the vectors of crystal fractionation. The technique is tested by calculating the precision of the equilibrium between three garnet compositional variables within the chemical system determined to be appropriate for each of a series of microprobe analyses from garnet. Application of the fractionation calculations in conjunction with the P–T estimates based on intersecting compositional isopleths provides a means of calculating P–T conditions of garnet growth that is based on individual point‐analyses on a garnet grain. Such spatially precise and easily obtainable P–T data allow for detailed parallel studies of the microstructural, the P–T, and the chemical evolution of metamorphosed pelites. This method provides a means of studying the dynamics of orogenic systems at a resolution that was previously unattainable.     

Optical and infrared diagnostics of SDSS galaxies in the SWIRE survey

We present the rest-frame optical and infrared colours of a complete sample of  1114 z < 0.3  galaxies from the Spitzer Wide-Area Infrared Extragalactic (SWIRE) Legacy Survey and the Sloan Digital Sky Survey (SDSS). We discuss the optical and infrared colours of our sample and analyse in detail the contribution of dusty star-forming galaxies and active galactic nuclei (AGN) to optically selected red sequence galaxies.
We propose that the optical  ( g − r )  colour and infrared  log( L ₂₄/ L _3.6)  colour of galaxies in our sample are determined primarily by a bulge-to-disc ratio. The  ( g − r )  colour is found to be sensitive to the bulge-to-disc ratio for disc-dominated galaxies, whereas the  log( L ₂₄/ L _3.6)  colour is more sensitive for bulge-dominated systems.
We identify ∼18 per cent (195 sources) of our sample as having red optical colours and infrared excess. Typically, the infrared luminosities of these galaxies are found to be at the high end of star-forming galaxies with blue optical colours. Using emission-line diagnostic diagrams, 78 are found to have an AGN contribution and 117 are identified as star-forming systems. The red  ( g − r )  colour of the star-forming galaxies could be explained by extinction. However, their high optical luminosities cannot. We conclude that they have a significant bulge component.
The number densities of optically red star-forming galaxies are found to correspond to ∼13 per cent of the total number density of our sample. In addition, these systems contribute ∼13 per cent of the total optical luminosity density, and 28 per cent of the total infrared luminosity density of our SWIRE/SDSS sample. These objects may reduce the need for 'dry mergers'.