Welcome

• Konrad Schmidt (HZDR)

Room: online

Introduction to observational schools in 2022

• Andreas Korn (Uppsala University, Sweden)

Room: online We will provide a brief overview on the planned CHETEC-INFRA Observation School and the planned NPA School in 2022, both schools including observation sessions with the Nordic Optical Telescope (NOT).

Tools and techniques for modelling stellar spectra in 1D/LTE

• Bertrand Plez (University of Montpellier, France)

Room: online First lecture

Moderated questions

• Camilla J. Hansen (TU Darmstadt, Germany)

Room: online

Tools and techniques for modelling stellar spectra beyond 1D/LTE

• Andy Gallagher (Leibnitz Institute for Astrophysics, Germany)

Room: online Second lecture

Moderated questions

• Arūnas Kučinskas (Vilnius University, Lithuania)

Room: online

Tracing the slow neutron capture process in AGB stars using Ba star abundances

• Borbála Cseh (Konkoly Thege Miklós Astronomical Institute, Hungary)

Room: online Barium (Ba) stars are polluted by material enriched in the slow neutron capture (s-process) elements synthesized in the interior of their former asymptotic giant branch (AGB) companion star, which is now a white dwarf. By comparing AGB nucleosynthesis models with different s-process elemental abundances derived from the largest homogeneous set of Ba giant star observations we can reach a better understanding of the s process in AGB stars. All the computed hs-type (La, Ce, and Nd) to ls- type (Y and Zr) element ratios show a clear increasing trend with decreasing metallicity. This trend is predicted by low-mass AGB models in which 13C is the main neutron source. We selected a sample of 28 Ba stars for which both self-consistent spectroscopic observation and analysis are available and stellar mass determinations, via positioning the star on the HR diagram and comparing with evolutionary tracks. For this sample stars we considered both previously (Y, Zr, Ce, and Nd) and recently derived (Rb, Sr, Nb, Mo, Ru, La, Sm, and Eu) elemental abundances. Then, we performed a detailed comparison of these s-process elemental abundances to different AGB nucleosynthesis models from the Monash and the FRUITY theoretical data sets. We simplified the binary mass transfer by calculating dilution factors to match the [Ce/Fe] value of each star when using different AGB nucleosynthesis models, and we then compared the diluted model abundances to the complete Ba star abundance pattern. Our comparison confirms that low mass (with initial masses roughly in the range 2–3 MSun), non-rotating AGB stellar models with 13C as the main neutron source are the polluters of the vast majority of the considered Ba stars, although some stars may represent the signature of a physical (e.g., mixing) and/or nucleosynthetic process that is not represented in the set of models considered here.

Moderated questions

• Andreas Korn (Uppsala University, Sweden)

Room: online

Evidence for rotation and mixing in a sample of young massive giant stars

• Linda Lombardo (Observatoire de Paris, France)

Room: online In the search of a sample of metal-poor bright giant stars using Strömgren photometry, we serendipitously found a sample of 26 young (ages younger than 1 Gyr) metal-rich giants, with masses between 2.5 and 6 solar masses. Ten of these stars also rotate rapidly (vsini > 10 km/s). The high stellar masses suggest that these stars were of spectral type A to B when on the main sequence. This evolutionary stage is not very well characterised by observations so far because of the short time spent by stars in this phase. The discovery of this sample of giant stars therefore allows us to study this evolutionary stage directly, and to compare their abundance pattern to that of main-sequence A and B stars. Moreover, it is an opportunity for testing the predictions of stellar evolutionary models in terms of the evolution of chemical abundances and rotational velocities. In this talk I will present how we derived the chemical abundances for 16 elements (C, N, O, Mg, Al, Ca, Fe, Sr, Y, Ba, La, Ce, Pr, Nd, Sm, and Eu) taking into account the effect of stellar rotation. I will also present the results we obtained and how they compare to the predictions of stellar evolution models.

Moderated questions

• Andreas Korn (Uppsala University, Sweden)

Room: online

Round table discussion Room: online Questions that were compiled in the chat during and after lectures and breakout session will be answered and discussed.