Seminarium odbywa się w środy o 11:15 w warszawskim oddziale Centrum Astronomicznego lub w wersji online na platformie Zoom. Językiem wykładowym jest angielski; seminarium prowadzi dr Stanisław Bajtlik (bajtlik@camk.edu.pl). Zapraszamy również osoby spoza Centrum Astronomicznego. W sprawie szczegółów technicznych prosimy kontaktować się e-mailowo z dr. Stanisławem Bajtlikiem.
Thibault Boulet (Institute of Astrophysics and Space Sciences, University of Porto, Portugal)
Understanding the Milky Way's formation and evolution requires precise stellar age determination across its components. Recent advances in asteroseismology, spectroscopy, stellar modeling, and machine learning, along with all-sky surveys, have provided reliable stellar age estimates. We aim to furnish accurate age assessments for the Main Red Star Sample within the APOGEE DR17 catalogue. Leveraging asteroseismic age constraints, we employ machine learning to achieve this goal. We explore optimal non-asteroseismic stellar parameters, including Teff, L, [C/N], [Mg/Ce], [α/Fe], U(LSR), and 'Z' vertical height from the Galactic plane, to predict ages via categorical gradient boost decision trees. Our model, trained on merged samples from TESS and APOKASC-2 catalogs, achieves a median fractional age error of 20.8%, with a relative difference between the learning curves of 4.77%. For stars older than 3 Gyr, the error ranges from 7% to 23%; for those between 1 and 3 Gyr, it is 26% to 28%; and for stars younger than 1 Gyr, it is 43%. Applied to 125,445 stars, our analysis confirms the flaring of the young Galactic disc and reveals an age gradient among the youngest Galactic plane stars. We also identify two groups of metal-poor ([Fe/H] < -1 dex) and young (Age < 2 Gyr) stars exhibiting peculiar chemical abundances and halo kinematics. One of these groups is likely a remnant of the third gas infall episode that started around 2.7 Gyr ago.
Journal Club odbywa się w poniedziałki o 11:00 w Sali Seminaryjnej warszawskiego Centrum Astronomicznego. Językiem wykładowym jest angielski; spotkania prowadzą Angelos Karakonstantakis, Gergely Hajdu i Fatemeh Kayanikhoo.