Wednesday Colloquium


"Time-dependent modeling of particle acceleration and cooling in blazars"

Anton Dmytriiev (North-West University, South Africa)

Flaring states of blazars are ideally suited to study the extreme physics of relativistic outflows. A thorough understanding of particle acceleration and cooling mechanisms operating in blazar jets can be achieved via physical modeling of varying multi-band flaring emission from radio up to gamma-ray range. The majority of the numerical codes developed for this task use a simplified continuous-loss description for the inverse Compton particle cooling. Such an approximation is however no longer valid in the Klein-Nishina (KN) regime. In our study, we explore the importance of non-continuous Compton cooling losses and their effect on the blazar electron spectrum and broad-band spectral energy distribution (SED) for typical physical conditions during blazar gamma-ray flares. We find that the non-continuous cooling can lead to a significant modification of the shape of the electron spectrum and SED, especially during flaring states of FSRQs characterized by high Compton dominance.


"Proto-neutron star evolution and neutrino interactions in hot and dense matter"

Micaela Oertel (LUTH, Meudon)

Neutrinos play an important role in compact star astrophysics: neutrino-heating is one of the main ingredients in core-collapse supernovae, neutrino-matter interactions determine the composition of matter in binary neutron star mergers and have among others a strong impact on conditions for heavy element nucleosynthesis and neutron star cooling is dominated by neutrino emission except for very old stars. Many works in the last decades have shown that in dense matter medium effects considerably change the neutrino-matter interaction rates, whereas many astrophysical simulations use analytic approximations which are often far from reproducing more complete calculations. In this talk I will present a scheme which allows to incorporate improved rates into simulations and show as an example results for the evolution of a proto-neutron star.


"Evolution of massive stars with new hydrodynamic wind models"

Alex Gormaz-Matamala (CAMK, Warsaw)

We present evolutionary models for a set of massive stars, introducing a new prescription for the mass loss rate obtained from hydrodynamic calculations in which the wind velocity profile and the line-acceleration are obtained in a self consistently way. Evolutionary models with the new recipe for mass loss retain more stellar mass through their evolution, which is expressed in larger radii and consequently more luminous tracks over the Hertzsprung-Russell diagram. Also, models with self-consistent winds predict a weaker braking in the rotational velocity and a more marked drift redwards of the evolutionary tracks across the HRD, as a direct consequence of the differences in the stellar angular momentum loss and in the rotational mixing. Together with the prediction of higher masses at the end of main sequence, self-consistent tracks also predicts a distribution of rotational velocities for Galactic O-type stars more in agreement with the diagnostics of recent surveys. Other hypothetical implications, such as the masses of Ofpe stars at the Galactic Centre or the contribution of the isotope Al-26 to the ISM, are open to discussion.



Hélio Perottoni



Anish Amarsi (Department of Physics and Astronomy, Uppsala University)


"Combining binary and asteroseismic information in stellar modelling"

Cole Johnston (Radboud University, Nijmegen, NL)

Large-scale high-precision space-based photometric missions have revealed that most stars are variable either through intrinsic (spots, pulsations) or external (eclipses) mechanisms. Fortunately, we can leverage the characteristics of this variability in order to learn something about stars. For instance, spots provide information on stellar rotation, pulsations reveal the interior structure of stars, and eclipses provide the opportunity to obtain highly precise estimates of the fundamental stellar parameters. Fortuitously, it is clear that many stars display multiple forms of variability. To this end, I will discuss my work in jointly modelling pulsating and eclipsing binary variables to cross-calibrate stellar evolutionary models at all masses across the Hertzsprung-Russell diagram.



Marcin Kuźniak (CAMK, AstroCent, Warsaw)



Alberto Martinez-Garcia (Instituto de Astrofísica de Canarias)



Philipp Kempski (Princeton University)



Jacek Ksawery Osinski (AstroCent/CAMK, Warsaw)