Stellar capture by an accretion disc

Long-term evolution of a stellar orbit captured by a massive galactic center via successive interactions with an accretion disc has been examined. An analytical solution describing evolution of the stellar orbital parameters during the initial stage of the capture was found. Our results are applicable to thin Keplerian discs with an arbitrary radial distribution of density and rather general prescription for the star-disc interaction. Temporal evolution is given in the form of quadrature which can be carried out numerically.Comment: Letter to MNRAS, 5 pages and 3 figures; also available at http://otokar.troja.mff.cuni.cz/user/karas/au_www/karas/papers.ht

Emission Line Profiles from Self-Gravitating Thin Disks

We have constructed general relativistic models of a stationary, axially symmnetric, Keplerian thin disk around a rotating black hole. We computed profiles of a spectral line, emitted in the inner region of the disk. In our models we have taken into account also the self-gravity of the disk. The aim of this work is to study gravitational effects on the line profiles in connection with the X-ray features observed in spectra of active galactic nuclei. In some cases, the calculated profiles are clearly affected by the disk gravity but relativistic dragging effects are found to be negligible.Comment: 26 pages, 8 figures, uuencoded postscript file, to appear in The Astrophysical Journal, Part I. Printed version available upon request from the author

Orbital Perturbations of the Galilean Satellites During Planetary Encounters

The Nice model of the dynamical instability and migration of the giant planets can explain many properties of the present Solar System, and can be used to constrain its early architecture. In the jumping-Jupiter version of the Nice model, required from the terrestrial planet constraint and dynamical structure of the asteroid belt, Jupiter has encounters with an ice giant. Here we study the survival of the Galilean satellites in the jumping-Jupiter model. This is an important concern because the ice-giant encounters, if deep enough, could dynamically perturb the orbits of the Galilean satellites, and lead to implausible results. We performed numerical integrations where we tracked the effect of planetary encounters on the Galilean moons. We considered three instability cases from Nesvorny & Morbidelli (2012) that differed in the number and distribution of encounters. We found that in one case, where the number of close encounters was relatively small, the Galilean satellite orbits were not significantly affected. In the other two, the orbital eccentricities of all moons were excited by encounters, Callisto's semimajor axis changed, and, in a large fraction of trials, the Laplace resonance of the inner three moons was disrupted. The subsequent evolution by tides damps eccentricities and can recapture the moons in the Laplace resonance. A more important constraint is represented by the orbital inclinations of the moons, which can be excited during the encounters and not appreciably damped by tides. We find that one instability case taken from Nesvorny & Morbidelli (2012) clearly fails this constraint. This shows how the regular satellites of Jupiter can be used to set limits on the properties of encounters in the jumping-Jupiter model, and help us to better understand how the early Solar System evolved.Comment: The Astronomical Journal, in pres