Szemináriumok

The Fundamental Parameters of Very Low Mass Stars

The role of molecular collisions in astronomy: towards non-LTE modelling of interstellar emission lines

Molecular clouds are active star-forming regions in the interstellar medium (ISM) and are therefore of particular interest for understanding the evolution of the early Universe. State-of-the-art ground-based and space telescopes are now providing brand new insights into the chemical composition and structure of matter in these clouds. However, detections in distant environments requires extensive support from both experimental and theoretical techniques. In interstellar clouds, local thermodynamic equilibrium conditions are usually not fulfilled (i.e. non-LTE conditions are present), so collisional and radiative processes compete to populate molecular levels. It is therefore important to explicitly take these processes into account for proper astrophysical modelling of the molecular emission lines detected from the ISM. The correct interpretation of the observations then allows to derive the abundance of the particular species, which also provides important details about the underlying physico-chemical processes. In my talk, I will briefly summarise our recent results on various molecular collision problems and highlight their relevance for astronomy. In particular, I will focus on the importance of accurate state-to-state collisional rate coefficients for radiative transfer astrophysical models.

Susan Pyne
University College London; UK

Weak gravitational lensing with the next generation of galaxy surveys

Weak lensing, the bending of light by the cosmological large-scale structure, has become an essential tool for cosmology. A new generation of very large galaxy surveys, for example the ESA Euclid survey, are just coming on stream. These so-called Stage IV surveys will produce a wealth of very accurate data which is optimised for weak lensing.

I will explain why weak lensing is such a useful technique, explore the current state of the field, and discuss some opportunities and challenges involved in analysing the vast amounts of data from the new surveys. In particular, I will highlight the challenge of controlling systematic uncertainties, especially the intrinsic alignment of galaxies, and discuss some ways of tackling these.

Nuclear reaction studies on radionuclides at LANSCE with a focus on the 56Ni(n,p) reaction for the interest of νp process

For reaching out radioactive isotopes relevant for the νp process nucleosynthesis, a new capability of producing radioactive isotopes at the Isotope Production Facility and performing direct measurements via (n,p) and (n,α) reactions has been commissioned at the Los Alamos Neutron Science Center (LANSCE). To answer the heavy element production puzzles in core-collapse supernova explosions, we studied the 56Ni(n,p) reaction, which has been identified as one of critical reactions during the np process. Using the hotLENZ (radioactive Low Energy NZ) instrument, the cross sections of 56,59Ni(n,p), 56Co(n,p), and 59Ni(n,α) reactions were first directly measured for deducing reaction rates. Updated 56Ni(n,p) and 56Co(n,p) reaction rates were compared with the current rates from REACLIB (Cyburt 2010), and were used in hydrodynamics calculations using the parameters from Wanajo et al. (2011) and Nishimura et al. (2019) along with our parameters. The summary of astrophysical impacts will be discussed in terms of potential further constrains of nuclear physics input to improve our understanding of the np process network calculations. Ongoing efforts on the radioactive 40K, 44Ti, and 26Al measurements and the status of the optimized solenoidal spectrometer development for radioactive nuclear reaction studies at LANSCE will be presented.