Lake District pioneers – the earliest footprints on land

New evidence reveals that the first arthropods colonized dry land over 450 million years ago, more than 20 million years before the appearance of vascular plants. Traditionally, it was thought that animals only emerged on to land after plants had become established, thus providing a plentiful new food source. The earliest known terrestrial trace fossils occur in volcanogenic sediments from the English Lake District. The trace fossils are thought to have been made on land by a small millipede-like creature. These rocks contain no other fossils.     

Fast quadratic power spectrum estimators and the E–B decomposition

We describe a fast, quadratic power spectrum estimator for cosmic microwave background polarization fields, based on heuristically-weighted correlation functions. The method can handle real-world effects such as inhomogeneous or correlated noise, and arbitrary sky cuts. A significant feature is that the electric and magnetic polarization powers are separated exactly in the mean, even for observations covering only a small region of the sky, and with a negligible increase in computational cost. The method is illustrated with simulations for a large-area survey, and a future, deep magnetic-polarization survey.     

High resolution spectra of galaxies

We present inversion techniques which aim at recovering the composite nature and the kinematics of a stellar population from its high resolution absorption line spectrum. The originality of the combined inversion is its potential to recover both the stellar content and the kinematics simultaneously. These techniques use new synthetic high resolution spectra produced by PéGASE and minimization algorithms. We apply them to mock data representing the bulge and disk population of the inner region of spiral galaxies. This revised version was published online in August 2006 with corrections to the Cover Date.     

Mars atmospheric escape and evolution; interaction with the solar wind

This tutorial deals with the question of atmospheric escape on Mars. After a brief introduction describing the general context of Mars escape studies, we will present in Section 2 a simplified theory of thermal escape, of both Jeans and hydrodynamic types. The phenomenon of hydrodynamic escape, still hypothetical and not proved to have ever existed on terrestrial planets, will be treated with the help of two well known examples: (i) the isotopic fractionation of xenon in Mars and Earth atmospheres, (ii) the paradox of missing oxygen in Venus atmosphere. In Section 3, a simplified approach of non-thermal escape will be developed, treating in a specific way the different kinds of escape (photochemical escape, ion sputtering, ion escape and ionospheric outflow). As a matter of illustration, some calculations of the relative contributions of these mechanisms, and of their time evolutions, will be given, and the magnitude of the total amount of atmosphere lost by non-thermal escape will be estimated. Section 4 will present the state of knowledge concerning the constraints derived from Mars isotopic geochemistry in terms of past escape and evolution. Finally, a few conclusions, which are more interrogations, will be proposed.     

Second-order theory of the rotation of an artificial satellite

This work presents the expansion of the second-order of an analytical theory of the attitude evolution of an artificial satellite perturbed by given torques. The first-order of the theory has already been presented by the author in Celestial Mechanics39 (1986) 309–327. It is a theory that is valid under very general conditions including slow rotation and inequal axes of inertia. The present theory is suitable for any internal or external disturbing forces producing the torques. A formal solution is expanded in the second-order according to powers of a small parameter characteristic of the order of magnitude of the disturbing torques. These torques are expanded in Fourier series and the theory applies whatever is the length of these series. The coefficients of the solution are given by an iterative formation law. The comparison of the results with a numerical integration based upon a HIPPARCOS model shows that the second order has brought an improvement to the theory by at least one order of magnitude over the results of the first order.     

Stellar kinematics and populations of early-type galaxies with the SAURON and OASIS integral-field spectrographs

We summarise the results and achievements of integral-field spectroscopy of early-type galaxies, observed as part of a survey using both the SAURON and OASIS spectrographs. From the perspective of integral-field spectroscopy, these otherwise smooth and featureless objects show a wealth of structure, both in their stellar kinematics and populations. We focus on the stellar content, and examine properties on both kiloparsec scales with SAURON, and scales of 100’s of parsecs with OASIS. These complementary studies reveal two types of kinematically distinct components (KDCs), differing primarily in their intrinsic sizes. In previous studies, KDCs and their host galaxies have generally been found to be unremarkable in other aspects. We show that large KDCs, typical of the well-studied cases, indeed show little or no age differences with their host galaxy. The KDCs detected with the higher spatial-resolution of OASIS are intrinsically smaller and include, in contrast, a significant fraction of young stars. We speculate on the relationship between KDCs and their host galaxies, and the implications for young populations in early-type galaxies.     

Scaling aspects of river flow routing

Scaling aspects of river flow routing are studied by comparing two flow routing schemes, one designed for use in coupled general circulation models (GCMs) and operated at large spatial scales (～350 km), and the other designed for use in typical hydrological applications at small spatial scales (～25 km). The same runoff data are used as input into the two routing schemes, and comparisons are made between mean annual, mean monthly and daily streamflow simulated at four locations within the Mackenzie River Basin. The results suggest that for the purpose of realistically modelling monthly streamflow at the mouth of the rivers in GCMs, flow routing at large spatial scales gives similar results. However, the amplitude of the annual streamflow cycle is slightly but characteristically larger, when routing is performed at large spatial scales. Flow routing at large spatial scales also results in overestimation of high flows, while low flows are underestimated. Copyright © 2001 John Wiley & Sons, Ltd.