My research centers on theoretical study of compact objects (neutron stars and black holes, pulsars), radiative processes (radiative transfer, stellar atmospheres, effects of strong magnetic fields), astrophysical fluid dynamics and MHD (accretion disks, density waves, binaries, stellar oscillations, gravitational collapse), gravitational waves, atomic physics and condensed matter in astrophysi...

The competition between impact erosion and impact supply of volatiles to planetary atmospheres can determine whether a planet or satellite accumulates an atmosphere. In the absence of other processes (e.g., outgassing), we find either that a planetary atmosphere should be thick, or that there should be no atmosphere at all. The boundary between the two extreme cases is set by the mass and veloc...

Spectroscopic studies of Planetary Nebulae (PNe) and H ii regions have driven much development in atomic physics. In the last few years the combination of a generation of powerful observatories, the development of ever more sophisticated spectral modeling codes, and large efforts on mass production of high quality atomic data have led to important progress in our understanding of the atomic spe...

We present the result of photo-ionizing modelling of the three planetary nebulae (PNe) A 20, A 15 and MeWe 1-3. All three objects are roughly roundish, highly excited and have a high galactic z. The PNe displayed low densities in the shell, but relatively dense halos. A low metallicity and a relative high electron temperature were found. Comparisons with radio observations confirmed the obtaine...

Planetary nebulae (PNe) have the potential to revolutionize our understanding of extragalactic stellar populations. Indeed, in many systems, bright PNe are the only individual objects identifiable from the ground, and, even more often, they are the only stars that are amenable to spectroscopy. We review the ways in which ensembles of PNe can be used to probe the metallicity, age, and history of...

Techniques have been devised for studying quantitatively the effects of air ions on microorganisms suspended in small drops. In smog-contaminated atmospheres moderate concentrations of positive and negative air ions exerted a protective effect on staphylococci by delaying the drop in pH customarily observed and by diminishing the rate of evaporation. In clean air higher concentrations of positi...

The water abundance in a planetary atmosphere provides a key constraint on the planet’s primordial origins because water ice is expected to play an important role in the core accretion model of planet formation. However, the water content of the solar system giant planets is not well known because water is sequestered in clouds deep in their atmospheres. By contrast, short-period exoplanets hav...

We have obtained 1.0—2.5μm spectra at R∼600 of 14 disk dwarfs with spectral types M6 to L7. For four of the dwarfs we have also obtained infrared spectra at R∼3000 in several narrow intervals. In addition, we present new L′ photometry for four of the dwarfs in the sample, which allows improved determinations of their bolometric luminosities. While obtaining the photometry we resolved the L-dwar...

Multi-frequency (X-ray, optical and radio) observations of galaxy clusters indicate that the atmospheres of these cosmic structures consist of a complex structure of thermal (hot and warm) and non-thermal (with different origin and spectra) distribution of electrons (and protons) which is, therefore, far from its modelling as a single, thermal electronic gas. This evidence requires to go beyond...

Processes relevant to Pluto’s atmosphere are discussed, and our current knowledge is summarized, including results of two stellar occultations by Pluto that were observed in 2002. The question of whether other Kuiper belt objects (KBOs) may have bound atmospheres is considered, and observational indicators for KBO atmospheres are described. The definitive detection of a KBO atmosphere could be ...