Wednesday Colloquium


"Mono-enriched stars and Galactic chemical evolution -- Possible biases in observations and theory"

Camilla J. Hansen (Max Planck Institute for Astronomy, Heidelberg, Germany)

A long sought for goal using chemical abundances is to understand the chemical evolution of the Galaxy and to pin down the nature of the first stars (Pop III). Metal-poor, old, unevolved stars are excellent tracers as they preserve the abundance pattern of the gas they were born from. Here we use a sample of 14 metal-poor stars observed at high resolution with PEPSI/LBT, to derive abundances of 32 elements. In this talk I present well-sampled abundance patterns for all stars obtained under the assumption of 1D, local thermodynamic equilibrium (LTE). To infer the nature of these stars, we compare unevolved cool stars, which have been enriched by a single event (``mono-enriched''), with yield predictions to pin down the mass and energy of the Pop III progenitor. A simple fit may bias our inferred mass and energy just as much as the simple 1D LTE abundance pattern. We therefore pursue with an improved fitting technique considering dilution and mixing and non-LTE corrected abundances. To date only few mono-enriched stars are known. Our sample presents Carbon Enhanced Metal-Poor (CEMP) stars some of which are promising bona fide second generation (mono-enriched) stars. Finally, we explore the predominant donor and formation site of the rapid and slow neutron-capture elements.


"Modifying the Inverse-square law of radiation for close-in exoplanets"

Mradumay Sadh (CAMK, Warsaw)

The inverse square law for calculating irradiance fails to predict the irradiation for planets close to their host stars. This makes it challenging to model the climate of these exoplanets through present GCM models. This talk would be about the attempt to revise the assumptions of this law and estimate correct values of irradiance for such planets with a geometrical analysis. Reference paper -


"How important is bulk viscosity in neutron star mergers?"

Mark Alford (Washington University in Saint Louis)

Neutron star mergers are laboratories for hot and dense nuclear matter. In a merger, the stellar material experiences large changes in temperature and density that happen in milliseconds. This means that mergers probe dynamical properties that may help us uncover the phase structure of ultra-dense matter. I will describe some of these properties, and then focus on the most promising, bulk viscosity. I will explain how bulk viscosity arises and how it might have a significant effect in a merger.

Due to the time difference the talk will be at 4:15 pm.