Final tidal evolution of orbit-orbit resonances

In this paper we describe a model for the tidal evolution of an orbit-orbit resonance between two satellites of the same planet. We let the system evolve till infinity or until the resonance is destroyed. We find that there are asymptotic values for the eccentricities and inclinations. We list the possible final stages that a resonance can achieve, we give a few examples, and finally we discuss the limitations of the model and its possible applications to real systems.     

Chemo-spectrophotometric evolution of spiral galaxies – IV. Star formation efficiency and effective ages of spirals

We study the star formation history of normal spirals by using a large and homogeneous data sample of local galaxies. For our analysis we utilize detailed models of chemical and spectrophotometric galactic evolution, calibrated on the Milky Way disc. We find that star formation efficiency is independent of galactic mass, while massive discs have, on average, lower gas fractions and are redder than their low-mass counterparts; put together, these findings convincingly suggest that massive spirals are older than low-mass ones. We evaluate the effective ages of the galaxies of our sample and we find that massive spirals must be several Gyr older than low-mass ones. We also show that these galaxies (having rotational velocities in the 80–400 km s⁻¹ range) cannot have suffered extensive mass losses, i.e. they cannot have lost during their lifetime an amount of mass much larger than their current content of gas+stars.     

The minimum orbital period in thermal time-scale mass transfer

We show that the usual picture of supersoft X-ray binary evolution as driven by conservative thermal time-scale mass transfer cannot explain the short orbital periods of RX J0537.7–7034 (3.5 h) and 1E 0035.4–7230 (4.1 h). Non-conservative evolution may produce such periods, but requires very significant mass loss, and is highly constrained.     

The effects of Population III stars on the chemical and photometrical evolution of ellipticals

We have studied the effects of a hypothetical initial generation containing very massive stars [   M > 100 M_⊙  , pair-creation supernovae] on the chemical and photometric evolution of elliptical galaxies. To this purpose, we have computed the evolution of a typical elliptical galaxy with luminous mass of the order of  10¹¹ M_⊙  and adopted chemical evolution models already tested to reproduce the main features of ellipticals. We have tested several sets of yields for very massive zero-metallicity stars: these stars should produce quite different amounts of heavy elements than lower-mass stars. We found that the effects of Population III stars on the chemical enrichment is negligible if only one or two generations of such stars occurred, whereas they produce quite different results from the standard models if they continuously formed for a period not shorter than 0.1 Gyr. In this case, the results are at variance with the main observational constraints of ellipticals such as the average  [〈α/ Fe〉_*]  ratio in stars and the integrated colours. Therefore, we conclude that if Population III stars ever existed they must have been present for a very short period of time and their effects on the following evolution of the parent galaxy must have been negligible. This effect is minimum if a more realistic model with initial infall of gas rather than the classic monolithic model is adopted. Ultimately, we conclude that there is no need to invoke a generation of very massive stars in ellipticals to explain their chemical and photometric properties.     

Partial derivatives of surface wave phase velocities for flat anisotropic models

Summary. Surface wave behaviour in flat anisotropic structures is first illustrated by performing an exact computation on a simple two-layer model. The variational procedure of Smith & Dahlen is then used to compute the partial derivatives of surface wave phase velocities with respect to the elastic parameters in more realistic earth models. Linear relationships between the partial derivatives for a general anisotropic structure and those for a transversely isotropic structure are derived. When considering waves propagating in a fixed direction, there are only four independent derivatives for Rayleigh waves, and two for Love waves. To avoid the lack of resolution in an inverse method, we propose to use physically constrained models. These results are illustrated by using a model with hexagonal symmetry and a symmetry axis oriented either vertically or horizontally. Quasi-Love- and quasi-Rayleigh-wave partial derivatives are computed for both axis orientations. Modes up to the second overtone and periods ranging between 45 and 130 s have been considered. Finally, anomalies of phase velocity are computed in an oceanic model made of 1/6 oriented olivine crystals with horizontal or vertical preferred orientations of the a -axis.     

Evolution of Polytropic Reimann Disks in Halos

The equilibrium of elliptical Riemann disks with a polytropic equation of state and their evolution under the influence of viscosity and gravitational radiation inside spheroidal halos with a relative surface mass density k. The evolutionary trajectory of a disk inside a halo with k<0.5, which is analogous to the evolution of an isolated disk, differs from that of a disk inside a denser halo.     

青藏块体东北缘地壳水平运动状态

应用青藏块体东北缘1999～2003年多期GPS观测资料，计算了不同时段GPS点水平运动速率。通过分析发现：甘青块体可分为东部块体和西部块体，东、西部块体的运动状态存在明显的差异；受2001年11月14日昆仑Ms8．1地震的影响，震后地壳运动状态发生了明显的改变。