Some Problems with Slow Rotation of CP Stars

Some difficulties in explaining the slow rotation of CP stars are discussed. The most likely hypotheses are (1) a loss of angular momentum involving a magnetic field during “pre-main sequence” evolution and (2) the slow rotation existed from the very start of the creation of these stars. The braking hypothesis is supported by only one property of CP stars— the lower the mass of the star is, the greater the difference between its average rotation velocity vsini and that of normal stars. On the other hand, there is another property— the lower the rotation speeds of CP stars are, the greater their fraction among normal stars. The latter property supports the hypothesis that the lower the initial rotation speed of a star is when it is created, the greater the probability will become chemically peculiar. This property is inherent in chemically peculiar stars both with and without a magnetic field. It is proposed that the cause of the slow rotation of CP stars must be sought in the very earliest phases of their formation, as should the cause of the separation into chemically peculiar magnetic, chemically peculiar nonmagnetic, and normal stars.__________Translated from Astrofizika, Vol. 48, No. 2, pp. 229–245 (May 2005).     

Low-cost volcano surveillance from space: case studies from Etna, Krafla, Cerro Negro, Fogo, Lascar and Erebus

 Satellite data offer a means of supplementing ground-based monitoring during volcanic eruptions, especially at times or locations where ground-based monitoring is difficult. Being directly and freely available several times a day, data from the advanced very high resolution radiometer (AVHRR) offers great potential for near real-time monitoring of all volcanoes across large (3000×3000 km) areas. Herein we describe techniques to detect and locate activity; estimate lava area, thermal flux, effusion rates and cumulative volume; and distinguish types of activity. Application is demonstrated using data for active lavas at Krafla, Etna, Fogo, Cerro Negro and Erebus; a pyroclastic flow at Lascar; and open vent systems at Etna and Stromboli. Automated near real-time analysis of AVHRR data could be achieved at existing, or cheap to install, receiving stations, offering a supplement to conventional monitoring methods. Received: 21 January 1997 / Accepted: 3 April 1997     

Simulations of deep pencil-beam redshift surveys

We create mock pencil-beam redshift surveys from very large cosmological N -body simulations of two cold dark matter (CDM) cosmogonies, an Einstein–de Sitter model ( τ CDM) and a flat model with Ω₀=0.3 and a cosmological constant (ΛCDM). We use these to assess the significance of the apparent periodicity discovered by Broadhurst et al. Simulation particles are tagged as 'galaxies' so as to reproduce observed present-day correlations. They are then identified along the past light-cones of hypothetical observers to create mock catalogues with the geometry and the distance distribution of the Broadhurst et al. data. We produce 1936 (2625) quasi-independent catalogues from our τ CDM (ΛCDM) simulation. A couple of large clumps in a catalogue can produce a high peak at low wavenumbers in the corresponding one-dimensional power spectrum, without any apparent large-scale periodicity in the original redshift histogram. Although the simulated redshift histograms frequently display regularly spaced clumps, the spacing of these clumps varies between catalogues and there is no 'preferred' period over our many realizations. We find only a 0.72 (0.49) per cent chance that the highest peak in the power spectrum of a τ CDM (ΛCDM) catalogue has a peak-to-noise ratio higher than that in the Broadhurst et al. data. None of the simulated catalogues with such high peaks shows coherently spaced clumps with a significance as high as that of the real data. We conclude that in CDM universes, the regularity on a scale of ∼130  h ⁻¹ Mpc observed by Broadhurst et al. has a priori probability well below 10⁻³.     

Star formation, massive stars, and super star clusters in nearby galaxies

The Square Kilometer Array (SKA) will enable studies of star formation in nearby galaxies with a level of detail never before possible outside of the Milky Way. Because the earliest stages of stellar evolution are often inaccessible at optical and near-infrared wavelengths, high spatial resolution radio observations are necessary to explore extragalactic star formation. The SKA will have the sensitivity to detect individual ultracompact HII regions out to the distance of nearly 50 Mpc, allowing us to study their spatial distributions, morphologies, and populations statistics in a wide range of environments. Radio observations of Wolf-Rayet stars outside of the Milky Way will also be possible for the first time, greatly expanding the range of conditions in which their mass loss rates can be determined from free-free emission. On a vastly larger scale, natal of super star clusters will be accessible to the SKA out to redshifts of nearly z 0.1. The unprecedented sensitivity of radio observations with the SKA will also place tight constraints on the star formation rates as low as 1M yr⁻¹ in galaxies out to a redshift of z 1 by directly measuring the thermal radio flux density without assumptions about a galaxy’s magnetic field strength, cosmic ray production rate, or extinction.     

An Historical Overview

Studies in extragalactic astronomy, galactic structure and the late stages of stellar evolution provide ample motivation for surveys of fields in the Galactic Halo. Apart from white dwarfs, blue stars had been regarded as luminous objects confined to star-forming regions in the Galactic Plane; finding them at high galactic latitudes attracted immediate interest, because their luminosities were intermediate between those of white dwarfs and blue Main Sequence stars. The study of blue stars away from the Galactic Plane was initiated by Greenstein; in due course effective temperatures (T _e ff), surface gravities (log g) and abundances showed these stars form what appeared to be a blue extension of the known Horizontal Branch (HB) in the Hertzsprung–Russell Diagram. Extended Horizontal Branch (EHB) stars were identified with Extreme Horizontal Branch stars in globular clusters. It was realised that HB and EHB stars must have formed as a consequence of mass-loss on the Giant Branch, either at or before the helium flash. Mass-loss on the Giant Branch leading to the formation of EHB stars was considered more likely for stars in binary systems. The scene was then set for three decades of EHB star research.     

Depositional and post‐depositional history of warm stage deposits at Knocknacran,Co. Monaghan,Ireland: implications for preservation of Irish last interglacial deposits

Organic‐rich deposits, uncovered during overburden removal from mantled gypsum karst at Knocknacran opencast gypsum mine, Co. Monaghan, are the best candidate to date for a last interglacial record in Ireland. The two till and organic‐rich deposits (preserved at different quarry elevations) were emplaced on to a Tertiary dolerite surface during high‐energy flood events and subsequently folded and faulted by movement towards sinkholes in underlying gypsum. Uranium–thorium disequilibrium dating suggests that the organic‐rich deposits in the upper section were hydrologically isolated at ca. 41 ka and those in the lower section at ca. 86 ka. Interpretation of the pollen content, although tentative because of the depositional and post‐depositional history of the material, suggests that the organic material originated in a warm stage possibly warmer than the post‐Eemian interstadials. The unusual setting of preservation may indicate that in situ, last interglacial deposits have generally been removed by erosion in Ireland. Copyright © 2004 John Wiley & Sons, Ltd.     

A comparative study of the zooplankton in two adjacent embayments,Port Phillip and Westernport Bays,Australia

We report on a year's study of spatial and seasonal patterns of zooplankton abundance in Port Phillip and Westernport Bays, July 1982 to August 1983. These two bays, closely adjacent on the southern coast of Victoria, Australia, differ in several respects: Port Phillip is a nearly landlocked bay with a broad basin, while Westernport is an open tidal embayment with extensive mud and seagrass banks. Both bays have a resident zooplankton fauna distinct from that of Bass Strait. Although these resident communities have many species in common, patterns of abundance and dominance are quite different. We found that the holoplankton of Port Phillip was about half copepods, mostly Paracalanus indicus, with 23% Caldocera and 21% larvaceans. Westernport Bay zooplankton was dominated by Acartia tranteri, with no resident cladoceran fauna. Bass Strait species were more often found in Westernport than in Port Phillip Bay, but the resident community of Port Phillip Bay was more similar to that of Bass Strait than to that of Westernport.Although this study was undertaken in an exceptionally dry year, the available historical data show that the overall patterns found in 1982–1983 are typical for these bays. The differences in community composition probably relate to differences in depth profile, predator abundance, and suspended matter between the bays.     

REMOTE SENSING FOREST BIOMASS: AN EVALUATION USING HIGH RESOLUTION REMOTE SENSOR DATA AND LOBLOLLY PINE PLOTS

Eight-year-old Loblolly pine (Pinus taeda) plots located in South Carolina were evaluated using high resolution aircraft multispectral scanner data to determine if biomass could be accurately measured. Sixteen pine plots located on both sandy and clay soils were treated with 0, 180, or 360 kg. (approximately 0, 400, or 800 lb.) of nitrogen per plot. Indices of biomass from remote sensing data were significantly correlated with in situ biomass measurements made in each plot. A ratio of infrared (.9–1.1 μm) and red (.65–.70 μm) channels yielded the best correlation. The indices were not sensitive to differences in soil type (sandy or clay).