A Hamiltonian theory for an elastic earth: First order analytical integration

In this article an approximate analytical integration is performed of the Hamiltonian corresponding to the rotational motion of an Earth whose elastic mantle is deformed by rotation and lunisolar attraction, using Deprit's perturbation method for the first order. Besides the usual terms, this Hamiltonian includes the perturbation of the kinetic energy and the elastic energy produced with the deformation, as well as their causes, the tidal and the centrifugal potential; these new terms have already been studied for the tidal deformation in previous articles (Getino and Ferrándiz, 1990a, 1990b). The effects of the deformation due to the centrifugal potential are studied in this article, following the same method as that used for the tidal deformation. Numerical tables of the periodic perturbations corresponding to the nutation in obliquity and longitude are obtained. As for the secular effects, a theoretical value of 457 days is obtained for Chandler's period.     

Self-consistent solutions of the semi-classical back-reaction equations with cosmological constant spatial curvature and perfect fluid

Exact solutions of the semi-classical Einstein equations with cosmological constant for conformally invariant free quantum fields in a general Robertson-Walker metric are found when a classical perfect fluid is present. There exist a one-parameter family of time-symmetric bouncing solutions that avoid the singularity and a one-parameter family which does not have particles horizons. The de Sitter solution is found to be stable, while the Einstein universe is unstable.     

Stability of the inflation in R2 cosmology with massless conformal quantum fields

A semiclassical higher-derivative theory of gravity is investigated for conformally invariant free quantum fields in homogeneous and isotropic spacetime with no cosmological constant nor classical source. In the spatially flat case the stability of the de Sitter solution is studied. Moreover, the Minkowski solution is found to be unstable.Fellow of the Consejo Nacional de Investigaciones Científicas y Técnicas.     

Results from the Eso Large Program on Transneptunian Objects and Centaurs

BVRI photometry of 107 TNOs and Centaurs establishes the range of spectral gradients to be between –5 to 55%/100 nm (with one exception). A cluster of very red Cubewanos is firmly identified in orbits of low inclination and eccentricity beyond 40 AU from the Sun. Further correlations between surface colours and dynamical parameters (inclination and perihelion distance) are suggested for Cubewanos and scattered disk objects, but lack complete confidence for their reality. Plutinos and Centaurs do not show any clear correlation between surface colours and orbital parameters. We present in this paper 12 spectra obtained in the visible region and nine of them for which we obtained also near infrared spectra up to 2.4 microns. A few other objects have been observed, but the data are still under reduction and analysis. The principal reported results obtained are: (i) a wide range of visible slopes; (ii) evidence for surface variations on 2001 PT₁₃; and (iii) possible detection of few percent of water ice (1999 TC_36}, 2000 EB₁₇₃, 1999 DE₉, 2001 PT₁₃, 2000 QC₂₄₃, 1998 SG₃₅).     

A Complete Microjansky Radio Survey

The Phoenix Deep Survey is an ongoing multi-wavelength survey of a 2^° diameter field aimed at studying the properties of the sub-mJy and μJy radio population. Here, we present the latest 1.4 GHz observations of this field. The new data, reaching a 5 σ flux level of 45 μJy at the centre of a 50′ diameter field, comprise more than 700 sources with flux densities less than 1 mJy (187 of which have S_1.4 < 100 μJy). This provides one of the deepest radio (1.4 GHz) surveys currently available. The 1.4 GHz source counts are presented and show a flattening down to the 50 μJy level. At flux densities around 300 μJy there are indications that the sources detected may exhibit higher clustering than those observed at higher flux levels. This suggests that deep radio surveys could be useful for studies of large-scale structure but it also presents a warning for the representativity of sources in deep pencil-beam radio surveys. The study of the optical counterparts of the μJy population seems to indicate that the median R magnitude starts to decrease below 100 μJy. Spectroscopic classification of a sample of sources in this survey confirms the trend for an increasing fraction of star-forming galaxies over other systems down to ～ 100 μJy.     

Remote sensing observations of biological material by LANDSAT along a tidal thermal front and their relevancy to the available field data

Two images recorded on two successive summer days by LANDSAT satellite over the western approaches to the English Channel show bright pattern of complex shape the origin of which is puzzling. Among the wavelength bands available on LANDSAT's multispectral scanner, these patterns are apparent only in the green region of the spectrum, and they are located towards the stratified side of a well marked tidal thermal front. Spectral signature analysis and available knowledge on hydrography and plankton in the area are used to derive a proposed interpretation. Phytoplankton would accordingly be the best candidate for being responsible for the observed patterns.     

A new method for the analysis of apsidal motions in eclipsing binaries

In this paper, a new method for the determination of apsidal motion parameters in eccentric eclipsing binaries is presented. A sequential procedure has been followed throughout allowing an automatized on-line computation of the elements and their accuracies as well as a more realistic fit to the observed times of minima. A determination of individual mean errors for the parameters of fit give us the possibility to compare the results with available theoretical models of stellar structure. In the procedure, we have introduced a determination of preliminary elements by means of Fourier transform and extended the practical equations to terms up to the fifth power of the eccentricity. An application to the well-known case of the eclipsing binary GL Car has been made. Our analysis shows an apsidal motion period of 25.3 years with a value of 0.152 for the orbital eccentricity.     

Elimination of the nodes in problems ofn bodies

In application of the Reduction Theorem to the general problem ofn (>-3) bodies, a Mathieu canonical transformation is proposed whereby the new variables separate naturally into (i) a coordinate system on any reduced manifold of constant angular momentum, and (ii) a quadruple made of a pair of ignorable longitudes together with their conjugate momenta. The reduction is built from a binary tree of kinetic frames Explicit transformation formulas are obtained by induction from the top of the tree down to its root at the invariable frame; they are based on the unit quaternions which represent the finite rotations mapping one vector base onto another in the chain of kinetic frames. The development scheme lends itself to automatic processing by computer in a functional language.     

On the detectability of H2S in Jupiter

The influence of hydrogen sulfide, a still-undetected key molecule for the Jovian atmospheric chemistry in the infrared spectrum, was investigated. Synthetic spectra including various vertical distribution profiles of H₂S have been computed and compared with observational data for Jupiter in the 2- to 15-cm^?1 and 1160- to 1200-cm^?1 spectral ranges. No firm conclusion about the presence of H₂S can be drawn from the latter spectral region because of large uncertainties in gaseous opacities. In the microwave range, H₂S is found to be a possible candidate to explain the measurements. Constraints to its vertical distribution which would imply a significant supersaturation in the troposphere are derived. Physical and chemical processes involving H₂S in the atmosphere are discussed in the light of this hypothesis.