Rameshan Thimmappa (Department of Physics, Villanova University)
Relativistic jets in radio galaxies provide unique laboratories for investigating particle acceleration and shock physics. Here, I present high-resolution X-ray and optical studies of two nearby radio galaxies, Pictor A and M87. In Pictor A, using Chandra observations, the western hotspot was resolved into a thin shock-front structure, revealing energy-dependent offsets between the X-ray/optical and radio emission. The hotspot also exhibits long-term flux variability and spectral steepening downstream of the shock. In addition, an X-ray filament has been detected in the eastern lobe of Pictor A. For M87, multi-epoch Chandra and Hubble observations of knot HST-1 in the jet reveal a correlation between flux and positional offset during its flare around 2005, along with substantial long-term flux variability and apparent superluminal motion. These observations further suggest that the X-ray and UV/optical emission may originate from physically distinct regions. Together, these studies demonstrate how spatially resolved imaging and multi-epoch variability analyses can probe the internal structure, dynamics, and high-energy synchrotron emission of relativistic jets in active galactic nuclei.
Alex Gormaz Matamala (Astronomical Institute of the Czech Academy of Sciences)
Mass loss shapes the evolution and final fates of massive stars through their OB, RSG and WR phases. Revised line-driven wind prescriptions predict weaker winds during the OB phases, spanning ~90% of a massive star's lifetime. We present evolutionary models from the Galactic Centre (Z=0.020) to the Small Magellanic Cloud (Z=0.002), exploring changes in HR diagram tracks, surface rotation and chemical enrichment. At high metallicity, weaker winds retain outer layers and slow surface chemical evolution; at low metallicity, they enhance rotational mixing and accelerate surface enrichment. At the Galactic Centre, reduced early mass loss yields less homogeneous Wolf-Rayet (WR) stars and fewer hydrogen-free WN stars, improving agreement with observations. We derive H, He and CNO abundances for Ofpe/WN9, WNL, WN/C and WC subtypes and propose a revised subtype classification for wind-collision bow shocks to inform accretion models for Sgr A*. We also investigate how self-consistent wind hydrodynamic profiles, replacing the beta-law, modify wind configurations, hydrogen columns and accretion rates in high-mass X-ray binaries. Finally, we examine line-driven wind prescriptions near the Eddington limit. We introduce an O-to-WR wind-transition criterion to replace the classical hydrogen mass-fraction threshold and study its impact in the generation of black holes progenitors of gravitational waves.
