X‐rays from young stars: A summary of highlights from the XMM‐Newton Extended Survey of the Taurus Molecular Cloud (XEST)

The XMM‐Newton Extended Survey of the Taurus Molecular Cloud (XEST) is a survey of the nearest large star‐forming region, the Taurus Molecular Cloud (TMC), making use of all instruments on board the XMM‐Newton X‐ray observatory. The survey, presently still growing, has provided unprecedented spectroscopic results from nearly every observed T Tauri star, and from ≈50% of the studied brown dwarfs and protostars. The survey includes the first coherent statistical sample of high‐resolution spectra of T Tauri stars, and is accompanied by an U ‐band/ultraviolet imaging photometric survey of the TMC. XEST led to the discovery of new, systematic X‐ray features not possible before with smaller samples, in particular the X‐ray soft excess in classical T Tauri stars and the Two‐Absorber X‐ray (TAX) spectra of jet‐driving T Tauri stars. This paper summarizes highlights from XEST and reviews the key role of this large project. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Angular velocity glitches of the Vela pulsar in a model with “centrifugal buoyancy” of vortices

The forces acting on the solid crust of a differentially rotating neutron star are examined when a nonuniform excess of chemical potential exists. The resultant of the external forces, a stress force, is expressed in terms of a centrifugal buoyancy force and the deformation of the star’s crust under the action of this force is calculated. It is shown that there is a region within the star where the resulting stresses lead to fracture of the crust when the difference in the angular velocities of the superfluid and normal components reaches a critical value. The “centrifugal buoyancy” mechanism for generating a glitch is used to estimate the parameters of glitches in the Vela pulsar. __________ Translated from Astrofizika, Vol. 50, No. 2, pp. 183–197 (May 2007).     

Evolution of the Radial Abundance Gradient and Cold Gas of the Galactic Disk

In order to understand the forming mechanism of the radial abun- dance gradient of the Galactic disk and the evolution of cold gas, we have con- structed a chemical evolution model of the Galactic disk, in which the star for- mation law concerned with molecular hydrogens is adopted, and the evolution of mass surface density is calculated for the molecular and atomic hydrogens separately, then the model predictions and the observed radial distributions of some physical quantities are compared. The result indicates that the model prediction is sensitive to the adopted infall timescale, the model which adopts the star formation law concerned with the molecular hydrogens can agree well with the major observed properties of the Galactic disk, especially can obtain naturally the radial oxygen abundance gradient of the Galactic disk, and the radial surface density profile of cold gas. The assumption of instantaneous or non-instantaneous recycling approximation has a small effect on the evolution of cold gas, especially in the case of rather low gas density.     

Simultaneous optical polarimetry and X-ray observations of the magnetic CV CP Tuc (AX J2315−592)

CP Tuc (AX J2315–592) shows a dip in X-rays which lasts for approximately half the binary orbit and is deeper in soft X-rays compared with hard X-rays. It has been proposed that this dip is due to the accretion stream obscuring the accretion region from view. If CP Tuc were a polar, as has been suggested, then the length of such a dip would make it unique amongst polars since in those polars in which a dip is seen in hard X-rays the dip lasts for only 0.1 of the orbit. We present optical polarimetry and RXTE observations of CP Tuc which show circular polarization levels of ∼10 per cent and find evidence for only one photometric period. These data confirm CP Tuc as a polar. Our modelling of the polarization data implies that the X-ray dip is due to the bulk of the primary accretion region being self-eclipsed by the white dwarf. The energy dependence of the dip is due to a combination of this self-eclipse and also the presence of an X-ray temperature gradient over the primary accretion region.     

The Glarus thrust: excursion guide and report of a field trip of the Swiss Tectonic Studies Group (Swiss Geological Society, 14.–16. 09. 2006)

This excursion guide results form a field trip to the Glarus nappe complex organized by the Swiss Tectonic Studies Group in 2006. The aim of the excursion was to discuss old and recent concepts related to the evolution of the Glarus thrust. The major aspects were (i) the interplay between deformation, fluid flow and geochemical alteration, (ii) episodic versus continuous deformation and fluid flow, and (iii) the link between large-scale structures, microstructures, and geochemical aspects. Despite 150 years of research in the Glarus nappe complex and the new results discussed during the excursion, there exist controversies that still are unsolved.     

Wavelet domain Bayesian denoising of string signal in the cosmic microwave background

An algorithm is proposed for denoising the signal induced by cosmic strings in the cosmic microwave background. A Bayesian approach is taken, based on modelling the string signal in the wavelet domain with generalized Gaussian distributions. Good performance of the algorithm is demonstrated by simulated experiments at arcminute resolution under noise conditions including primary and secondary cosmic microwave background anisotropies, as well as instrumental noise.     

The population of pulsars with interpulses and the implications for beam evolution

The observed fraction of pulsars with interpulses, their period distribution and the observed pulse width versus pulse period correlation are shown to be inconsistent with a model in which the angle α between the magnetic axis and the rotation axis is random. This conclusion appears to be unavoidable, even when non-circular beams are considered. Allowing the magnetic axis to align from a random distribution at birth with a time-scale of  ∼7 × 10⁷ yr  can, however, explain those observations well. The time-scale derived is consistent with that obtained via independent methods. The probability that a pulsar beam intersects the line of sight is a function of the angle α and therefore beam evolution has important consequences for evolutionary models and for estimations of the total number of neutron stars. The validity of the standard formula for the spin-down rate, which is independent of α, appears to be questionable.