Theoretical astrophysics and plasma physics at RPC

Abstract:

An extension of Schwarzschild's galaxy-building technique is presented that, for the first time, enables one to build Schwarzschild models with known distribution functions (DFs). The new extension makes it possible to combine a DF that depends only on classical integrals with orbits that respect non-classical integrals. With such a combination, Schwarzschild's orbits are used only to represent the difference between the true galaxy DF and an approximating classical DF. The new method is used to construct a dynamical model of the inner Galaxy. The model is based on an orbit library that contains 22168 regular orbits. The model aims to reproduce the three-dimensional mass density of Binney, Gerhard & Spergel (1997), which was obtained through deprojection of the COBE surface photometry, and to reproduce the observed kinematics in three windows - namely Baade's Window and two off-axis fields. The model fits essentially all the available data within the innermost 3 kpc. The axis ratio and the morphology of the projected density contours of the COBE bar are recovered to good accuracy within corotation. The kinematic quantities - the line-of-sight streaming velocity and velocity dispersion, as well as the proper motions when available - are recovered, not merely for the fitted fields, but also for three new fields. The dynamical model deviates most from the input density close to the Galactic plane just outside corotation, where the deprojection of the surface photometry is suspect. The dynamical model does not reproduce the kinematics at the most distant window, where disk contamination may be severe.

Abstract:

We consider several protostellar systems in which either a precessing jet or at least two misaligned jets have been observed. We assume that the precession of jets is caused by tidal interactions in noncoplanar binary systems. For Cep E, V1331 Cyg, and RNO 15-FIR, the inferred orbital separations and disk radii are in the range 4-160 AU and 1-80 AU, respectively, consistent with those expected for pre-main-sequence stars. Furthermore, we assume or use the fact that the source of misaligned outflows is a binary and evaluate the length scale over which the jets should precess as a result of tidal interactions. For T Tau, HH1 VLA 1/2, and HH 24 SVS63, it may be possible to detect a bending of the jets rather than "wiggling." In HH 111 IRS and L1551 IRS5, wiggling may be detected on the current observed scale. Our results are consistent with the existence of noncoplanar binary systems in which tidal interactions induce jets to precess.

Abstract:

The deprojection of the surface brightness distribution of an axisymmetric galaxy does not have a unique solution unless the galaxy is viewed precisely edge-on. I present an algorithm that finds the full range of smooth axisymmetric density distributions consistent with a given surface brightness distribution and inclination angle, and use it to investigate the effects of this non-uniqueness on the line-of-sight velocity profiles (VPs) of two-integral models of both real and toy discy galaxies viewed at a range of inclination angles. Photometrically invisible face-on discs leave very clear signatures in the minor-axis VPs of the models (Gauss-Hermite coefficients h4 ≳ 0.1), provided the disc-to-bulge ratio is greater than about 3 per cent. I discuss the implications of these hitherto neglected discs for dynamical modelling.