The quasi-steady state cosmology: Some recent developments

This paper summarises the recent work on the quasi-steady state cosmology. This includes, the theoretical formulation and simple exact solutions of the basic equations, their relationship to observations, the stability of solutions and the toy model for understanding the growth of structures in the universe.     

New models of interstellar gas–grain chemistry – III. Solid CO2

Solid CO₂ is observed to be an abundant interstellar ice component towards both quiescent clouds and active star-forming regions. Our recent models of gas–grain chemistry, appropriate for quiescent regions, severely underproduce solid CO₂ at the single assumed gas density and temperature. In this paper, we investigate the sensitivity of our model results to changes in these parameters. In addition, we examine how the nature of the grain surface affects the results and also consider the role of the key surface reaction between O and CO. We conclude that the observed high abundance of solid CO₂ can be reproduced at reasonable temperatures and densities by models with diffusive surface chemistry, provided that the diffusion of heavy species such as O occurs efficiently.     

HD 9770, a southern active-chromosphere system

The visual triple system HD 9770 (BB Scl) has been the subject of a four-year programme of UVB ( RI )_C photometry and H α échelle spectroscopy. Analysis of the data obtained over that period shows that star B, and probably also star A, of HD 9770 is a binary. The A system comprises a K1V star, which may be in a binary system with another K dwarf. The B system is an eclipsing binary of the BY Dra type in which both stars are chromospherically active. An orbital period of 0.476 525±0.000 013 d has been derived from the light curve in V . Physical parameters derived from analysis of the light curves in UBV ( RI )_C are presented.     

An iterative technique for solving equations of statistical equilibrium

Superlevel partitioning is combined with a simple relaxation procedure to construct an iterative technique for solving equations of statistical equilibrium. In treating an N -level model atom, the technique avoids the N ³ scaling in computer time for direct solutions with standard linear equation routines and also does not fail at large N due to the accumulation of round-off errors. As a consequence, the technique allows detailed model atoms with N ≳10³ , such as those required for iron peak elements, to be incorporated into diagnostic codes for analysing astronomical spectra. Tests are reported for a 394-level Fe  ii ion and a 1266-level Ni  i – iv atom.     

Monte Carlo simulation of scintillation crystal detector for formation element logging

Formation elements logging is a neutron gamma spectroscopy logging technique used to acquire the content of elements and minerals by recording the gamma ray produced by the reaction of neutron and elemental nucleus in the formation. It has a wide usage in discriminating complex lithology and evaluating unconventional reservoir. The Monte Carlo simulation model of formation elements logging tool is established in this paper, with which the effects of tool parameters including the material and length of the scintillation crystal and source spacing on logging responses are modeled. The results show that the energy response of LaBr_3: Ce crystal is better than others, and the detection efficiency increases with the crystal length but decrease with source spacing. The above results may be used as a reference for optimizing the tool structure design.     

A numerical method for the study of shear band propagation in soft rocks

This paper investigates the possibility of interpreting progressive shear failure in hard soils and soft rocks as the result of shear propagation of a pre‐existing natural defect. This is done through the application of the principles of fracture mechanics, a slip‐weakening model (SWM) being used to simulate the non‐linear zone at the tips of the discontinuity. A numerical implementation of the SWM in a computation method based on the boundary element technique of the displacement discontinuity method (DDM) is presented. The crack and the non‐linear zone at the advancing tip are represented through a set of elements, where the displacement discontinuity (DD) in the tangential direction is determined on the basis of a friction law. A residual friction angle is assumed on the crack elements. Shear resistance decreases on elements in the non‐linear zone from a peak value at the tip, which is characteristic of intact material, to the residual value. The simulation of a uniaxial compressive test in plane strain conditions is carried out to exemplify the numerical methodology. The results emphasize the role played by the critical DD on the mechanical behaviour of the specimen. A validation of the model is shown through the back analysis of some experimental observations. The results of this back analysis show that a non‐linear fracture mechanics approach seems very promising to simulate experimental results, in particular with regards to the shear band evolution pattern. Copyright © 2009 John Wiley & Sons, Ltd.     

Massive star formation in galaxies: radiative transfer models of the UV to millimetre emission of starburst galaxies

We present illustrative models for the UV to millimetre emission of starburst galaxies which are treated as an ensemble of optically thick giant molecular clouds (GMCs) centrally illuminated by recently formed stars. The models follow the evolution of the GMCs owing to the ionization-induced expansion of the H  ii regions and the evolution of the stellar population within the GMC according to the Bruzual & Charlot stellar population synthesis models. The effect of transiently heated dust grains/PAHs on the radiative transfer, as well as multiple scattering, is taken into account.
The expansion of the H  ii regions and the formation of a narrow neutral shell naturally explain why the emission from PAHs dominates over that from hot dust in the near- to mid-infrared, an emerging characteristic of the infrared spectra of starburst galaxies.
The models allow us to relate the observed properties of a galaxy to its age and star formation history. We find that exponentially decaying 10⁷–10⁸ yr old bursts can explain the IRAS colours of starburst galaxies. The models are also shown to account satisfactorily for the multiwavelength data on the prototypical starburst galaxy M82 and NGC 6090, a starburst galaxy recently observed by ISO . In M82 we find evidence for two bursts separated by 10⁷ yr. In NGC 6090 we find that at least part of the far-infrared excess may be due to the age of the burst (6.4×10⁷ yr). We also make predictions about the evolution of the luminosity of starbursts at different wavelengths which indicate that far-infrared surveys may preferentially detect older starbursts than mid-infrared surveys.     

On the migration of a system of protoplanets

The evolution of a system consisting of a protoplanetary disc with two embedded Jupiter-sized planets is studied numerically. The disc is assumed to be flat and non-self-gravitating; this is modelled by the planar (two-dimensional) Navier–Stokes equations. The mutual gravitational interaction of the planets and the star, and the gravitational torques of the disc acting on the planets and the central star are included. The planets have an initial mass of one Jupiter mass M _Jup each, and the radial distances from the star are one and two semimajor axes of Jupiter, respectively.
During the evolution a joint wide annular gap is created by the planets. Both planets increase their mass owing to accretion of gas from the disc: after about 2500 orbital periods of the inner planet it has reached a mass of 2.3  M _Jup, while the outer planet has reached a mass of 3.2  M _Jup. The net gravitational torques exerted by the disc on the planets result in an inward migration of the outer planet on time-scales comparable to the viscous evolution time of the disc. The semimajor axis of the inner planet remains constant as there is very little gas left in its vicinity to induce any migration. When the distance of close approach eventually becomes smaller than the mutual Hill radius, the eccentricities increase strongly and the system may become unstable.
If disc depletion occurs rapidly enough before the planets come too close to each other, a stable system similar to our own Solar system may remain. Otherwise the orbits may become unstable and produce systems like υ And.     

Galaxy destruction and diffuse light in clusters

Deep images of the Centaurus and Coma clusters reveal two spectacular arcs of diffuse light that stretch for over 100 kpc, yet are just a few kiloparsecs wide. At a surface brightness of m _b ∼27–28 mag arcsec⁻² , the Centaurus arc is the most striking example known of structure in the diffuse light component of a rich galaxy cluster. We use numerical simulations to show that the Centaurus feature can be reproduced by the tidal debris of a spiral galaxy that has been tidally disrupted by the gravitational potential of NGC 4709. The surface brightness and narrow dimensions of the diffuse light suggest that the disc was corotating with its orbital path past pericentre. Features this prominent in clusters will be relatively rare, although at fainter surface brightness levels the diffuse light will reveal a wealth of structure. Deeper imaging surveys may be able to trace this feature for several times its presently observed extent, and somewhere along the tidal debris, a fraction of the original stellar component of the disc will remain bound, but transformed into a faint spheroidal galaxy. It should be possible to confirm the galactic origin of the Centaurus arc by observing planetary nebulae along its length with redshifts close to that of NGC 4709.