Infrared–red cores in nearby elliptical galaxies

We present the Spitzer Space Telescope Infrared Array Camera observations for a sample of local elliptical galaxies to study later stages of active galactic nucleus (AGN) activity. A sample of 36 elliptical galaxies is selected from the Palomar spectroscopic survey. We detect nuclear non-stellar infrared emission in nine of them. There is unambiguous evidence of circumnuclear dust in these nine galaxies in their optical images. We also find a remarkable correlation between the infrared excess emission and the nuclear radio/X-ray emission, suggesting that infrared excess emission is tightly related to nuclear activity. The possible origin of infrared excess emission from hot dust heated by the central AGN is supported by the spectral indices of the infrared excess emission.     

A search for high-redshift molecular absorption lines towards millimetre-loud, optically faint quasars

We describe initial results of a search for redshifted molecular absorption towards four millimetre-loud, optically faint quasars. A wide frequency bandwidth of up to 23 GHz per quasar was scanned using the Swedish–ESO Submillimetre Telescope at La Silla. Using a search list of commonly detected molecules, we obtained nearly complete redshift coverage up to   z _abs= 5  . The sensitivity of our data is adequate to have revealed absorption systems with characteristics similar to those seen in the four known redshifted millimetre-band absorption systems, but none were found. Our frequency-scan technique nevertheless demonstrates the value of wide-band correlator instruments for searches such as these. We suggest that a somewhat larger sample of similar observations should lead to the discovery of new millimetre-band absorption systems.     

A genetic algorithm for the non-parametric inversion of strong lensing systems

We present a non-parametric technique to infer the projected mass distribution of a gravitational lens system with multiple strong-lensed images. The technique involves a dynamic grid in the lens plane on which the mass distribution of the lens is approximated by a sum of basis functions, one per grid cell. We used the projected mass densities of Plummer spheres as basis functions. A genetic algorithm then determines the mass distribution of the lens by forcing images of a single source, projected back on to the source plane, to coincide as well as possible. Averaging several tens of solutions removes the random fluctuations that are introduced by the reproduction process of genomes in the genetic algorithm and highlights those features common to all solutions. Given the positions of the images and the redshifts of the sources and the lens, we show that the mass of a gravitational lens can be retrieved with an accuracy of a few percent and that, if the sources sufficiently cover the caustics, the mass distribution of the gravitational lens can also be reliably retrieved. A major advantage of the algorithm is that it makes full use of the information contained in the radial images, unlike methods that minimize the residuals of the lens equation, and is thus able to accurately reconstruct also the inner parts of the lens.     

On the mode of propagation of light

Starting from the fundamental assumptions of the special theory of relativity which do not take into consideration gravitational effects the isotropic propagation of light and how to check experimentally the mode of propagation have been analyzed.     

The yield of ionization in critical ionization velocity space experiments

We compare the conditions in laboratory and space critical ionization velocity (CIV) experiments. One significant difference that comes to light is the rapid expansion of the neutral cloud in space experiments, which does not take place in the laboratory. This has important ramifications for the ultimate ionization yield if there is a time delay in the ignition of the CIV discharge. We find that a simple kinetic model implies that the delay time of CIV ignition is a critical factor in determining the ultimate yield of the experiment. Although the delay time is difficult to calculate precisely, we provide some estimates that predict low CIV yield for typical space experimental geometries, densities and expansion rates. We examine the possibility of the variation of experimental conditions to maximize yield, but find that natural limitations in the design of space experiments may lead to low yields in the best of circumstances. This implies that experiments to date neither prove nor disprove the relevance of the CIV process to cosmology.     

Eruptions of comet Hale-Bopp at 6.5 AU

The prodigious output of dust and CO observed in comet Hale-Bopp at a heliocentric distance of 6.5 AU is strongly suggestive of high-pressure release of material from liquified subsurface domains rather than thermal evaporation from a sunlit patch of frozen CO.     

Meteoroid orbital characteristics by radar surveilence

H.F. radars are a powerful diagnostic for examining the orbits and spatial characteristics of the dust-meteoroid complex. Data on those properties are essential in realistic studies of the dynamics of small bodies in the solar system. An outline is here presented of the various programmes and their techniques employed in radar operations over the last 40 years. The particular value and contribution of radar facilities and comparisons with other methods is emphasised. Some of the features of the only current routine survey are discussed and, to illustrate to power of the system, examples of the types of data presentation are given.     

Circumstellar dynamics and transfer

This paper is both a review and a presentation of new models. Observation and modelization of circumstellar envelopes of early type or late type stars are now quickly evolving because of new techniques and facilities for observations, and increased power of computers. More and more complex physical phenomena involved in mass driving can now be modelized, at many different size scales. While most of models were previously based on informations derived from spectrophotometric data only or on measurements concerning objects observed with no spatial resolution, observations at much increased angular resolution can provide constraints on models of these phenomena. Theory and modelization must take this new situation into account. Two approaches are possible and effectively used. On the one hand, dynamical/physical self consistent models can be built; on the other hand, elaborate semi-empirical models including complicated distributions of matter with asymmetries (3D models) can be built and fitted for direct comparison with results of High Angular Resolution Measurements. Adding such constraints to classical constraints leads to a new insight in the physics of circumstellar matter and, through it, of stellar and interstellar evolution. Two examples have been chosen, in which new models are presented and assuming or not spherical symmetry is carefully discussed:

?Circumstellar matter around evolved stars

?Shock waves propagating in the circumstellar matter around evolved stars.

     

Search for Water in Martian Soil Using Global Neutron Mapping by the Russian HEND Instrument Onboard the US 2001 Mars Odyssey Spacecraft

We present the first results of the global neutron mapping of Mars by the Russian High-Energy Neutron Detector (HEND) onboard the US 2001 Mars Odyssey spacecraft. Global neutron maps of Mars in various spectral ranges allow the content of water ice and adsorbed and bound water in a near-surface layer of the planet 1 to 2 m in thickness to be estimated. Huge regions of permafrost with a high (several tens of percent by weight) content of water ice are shown to be present in the north and the south of Mars. The continuous observations of Mars for 12 months, from February 18, 2002, through February 8, 2003, are indicative of significant seasonal variations on Mars where the transition from northern winter to northern summer occurred.     

The Influence of Reactive Torques on Comet Nucleus Rotation

Reactive torques, due to anisotropic sublimation on a comet nucleus surface, produce slow variations of its rotation. In this paper the secular effects of this sublimation are studied. The general rotational equations of motion are averaged over unperturbed fast rotation around the mass center (Euler-Poinsot motion) and over the orbital comet motion. We discuss the parameters that define typical properties of the rotational evolution and discover different classifications of the rotational evolution. As an example we discuss some possible scenarios of rotational evolution for the nuclei of the comets Halley and Borrelly.