Wednesday Colloquium


"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.


"The chemodynamical nature of the stellar overdensities in the Milky Way"

Hélio Perottoni (University of São Paulo, Brazil and CAMK, Warsaw)

Over the past two decades, several stellar structures have been discovered both near the Galactic plane and in the halo. Some of the most intriguing of these structures are stellar overdensities, which are tenuous and spatially extended clouds of stars. Those stellar overdensities are identified as stellar count excesses in a given region of the sky when compared to other Galactic halo fields. Their nature has been debated since their discovery between an in situ and an ex-situ origin, although it seems that a consensus has finally been reached. In spite of this, there are still open questions regarding their characterization and how and when they formed. In this talk, I will discuss the nature of halo stellar overdensities and the characterization of disk stellar overdensities. I will present (i) a historical overview of these structures; (ii) the results from chemodynamical analyses our group performed for several of them.


"Carbon, oxygen, and iron abundances with 3D non-LTE models"

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

Spectroscopic analyses of stellar chemical compositions are model-dependent, and shortcomings in the models often limit the accuracy of the final results. For late-type stars like our Sun, two of the main problems in present-day methods are that they assume the stellar atmosphere is a) one-dimensional (1D) and hydrostatic, and b) satisfies local thermodynamic equilibrium (LTE). We can relax these assumptions simultaneously by performing detailed 3D non-LTE radiative transfer post-processing of 3D radiative-hydrodynamic model stellar atmospheres. I shall briefly describe this approach, and then illustrate its impact on carbon, oxygen, and iron abundances in late-type stars, and thereby on our understanding of stars and of the Galaxy.


"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.