Jagbir S. Hooda

Jet propagation and the asymmetries of CSS radio sources

As Compact Steep Spectrum radio sources have been shown to be more asymmetrical than larger sources of similar powers, there is a high probability that they interact with an asymmetric medium in the central regions of the host elliptical galaxy. We consider a simple analytical model of the propagation of radio jets through a reasonable asymmetric environment and show that they can yield the range of arm-length and luminosity asymmetries that have been observed. We then generalize this to allow for the effects of orientation, and quantify the substantial enhancements of the asymmetries that can be produced in this fashion. We present two-dimensional and three-dimensional simulations of jets propagating through multi-phase media and note that the results from the simulations are also broadly consistent with the observations.

Tomographic Separation of Composite Spectra. V. The Triple Star System 55 Ursae Majoris

We present moderate-resolution spectra obtained with the Georgia State University Multi-Telescope Telescope of 55 UMa, a triple system consisting of a 2.55 day spectroscopic binary and a third star in a 1873 day orbit (detected by speckle interferometry). We observed the spectral lines of all three stars, and we present radial velocity curves for both the close and wide orbits. We also present new speckle interferometric measurements and a revised solution of the astrometric (wide) orbit. The spectrum of each star was reconstructed using Doppler tomography, and we measured ratios of Fe I and Fe II lines in both the reconstructions and model synthetic spectra to estimate the stellar effective temperatures. These temperatures correspond to spectral types of A1 V and A2 V for the close pair and A1 V for the distant third star. We show that the metallic lines of the close pair are systematically strong, and we suggest that both objects are moderate Am stars. All the components have masses close to 2 M☉, and continued spectroscopic and astrometric observations will yield precise masses and absolute magnitudes.

Radio jet interactions with massive clouds

Three-dimensional simulations of light hydrodynamic jets are computed using the Zeus-3D code. We employ parameters corresponding to moderate to high power radio jets emerging through a galactic atmosphere or halo, and eventually crossing a tilted pressure matched interface with a hotter intracluster medium. These simulations aim the jets so that they hit massive dense clouds within the galactic halo. Such clouds are set up with radii several times that of the jet, and nominally correspond to giant molecular cloud complexes or small cannibalized galaxies. We find that powerful jets eventually disperse the clouds, but that, for the off-center collisions considered, non-axisymmetric instabilities are induced in those jets. Those instabilities grow faster for lower Mach number jets, and can produce disruptions substantially sooner than occurred in our earlier work on jets in the absence of collisions with massive clouds. Such interactions could be related to some Compact Steep Spectrum source morphologies. Very weak jets can be effectively halted by reasonably massive clouds, and this may have relevance for the paucity of radio jets in spiral galaxies. Slow, dense jets may be bent, yet remain stable for fairly extended times, thereby explaining some Wide-Angle-Tail and most “dog-leg” morphologies.