Rovibrational excitation of HD in collisions with atomic and molecular hydrogen

We have computed cross-sections and rate coefficients for rovibrational transitions in HD, induced by collisions with atomic and molecular hydrogen. We employed fully quantum-mechanical methods and the potential of Boothroyd et al. for H–HD, and that of Schwenke for H₂–HD. The rate coefficients for vibrational relaxation v =1→0 of HD are compared with the corresponding values for H₂. The influence of vibrationally excited channels on the rate coefficients for rotational transitions within the v =0 vibrational ground state of HD is shown to be small at T =500 K, where T is the kinetic temperature. The rate coefficients, for 100 T 2000 K, are available from http://ccp7.dur.ac.uk/.     

Astrophysical applications of a boundary integral method for fluid dynamics

A boundary integral formulation for the dynamics of incompressible, inviscid, self-gravitating bodies is described. The method is applied to several problems of astrophysical interest: spheroidal equilibria (Maclaurin and Jeans), oscillations, and a simple version of tidal encounter and breakup.     

On accretion flow penetration of magnetospheres

We address the problem of plasma penetration of astrophysical magnetospheres, an important issue in a wide variety of contexts, ranging from accretion in cataclysmic variables to flows in protostellar systems. We point out that under well-defined conditions, penetration can occur without any turbulent mixing (driven, for example, by Rayleigh–Taylor or Kelvin–Helmholtz instabilities) caused by charge polarization effects, if the inflowing plasma is bounded in the direction transverse to both the flow velocity and the magnetic field. Depolarization effects limit the penetration depth, which nevertheless can, under specific circumstances, be comparable to the size of the magnetosphere. We discuss the effect of ambient medium on plasma propagation across the stellar magnetic field and determine the criteria for deep magnetosphere penetration. We show that, under conditions appropriate to magnetized white dwarfs in AM Her type cataclysmic variables, charge polarization effects can lead to deep penetration of the magnetosphere.     

A 20 cm2 CCD mosaic camera for a dark matter search part I : Mechanics,optics and cryogeny

A 20cm ² CCD mosaic camera has been especially built to search for dark galactic halo objects by the gravitational microlensing effect. The sensitive area is made of 16 edge-buttable CCDs developped by Thomson-CTS, with 23×23 µm ² pixels. The 35 kg camera housing and mechanical equipment is presented. The associated electronics and data acquisition system are described in a separate paper. The camera resides at the focal plane of a 40 cm, f/10, Ferson reflector. The instrument has been in operation since December 1991 at the La Silla Observatory (ESO).