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© Gustavo Medina Toledo

Unveil­ing the Galac­tic History with Pulsat­ing Variable Stars

Gustavo Medina Toledo — Hector Fellow Eva Grebel

This project aims to explore the use of young and old pulsat­ing variable stars to improve our current under­stand­ing of the Milky Way. This will be achieved by perform­ing a novel study of the kinemat­ics, ages and chemi­cal compo­si­tions of Cepheids and RR Lyrae stars which, in spite of being arche­types of differ­ent stellar popula­tions, repre­sent key tracers of the recent star forma­tion and assem­bly history of the Galaxy.

The Milky Way's assem­bly history is still not fully under­stood, and Galac­tic archae­ol­ogy studies strive to recon­struct its forma­tion from present day stellar popula­tions. In that sense, pulsat­ing variable stars are impor­tant since they trace popula­tions in identi­fi­able evolu­tion­ary phases. In this work, I will study Cepheids and RR Lyrae stars, which are young/old variables (respec­tively) commonly used as precise distance indicators.

Super­vised by Hector Fellow Eva Grebel, I will analyze Cepheids in systems formed at the same time and under the same condi­tions. These coeval ensem­bles serve as cosmic labora­to­ries to get indepen­dent estima­tions of the age of the Cepheids they host. To deter­mine the member­ship of these stars to their host clusters, I will use data from the Gaia mission, since it provides kinemat­ics with an unprece­dented preci­sion and high-quality. This work will permit a direct calibra­tion of the Cepheid period-age relation, neces­sary to use them as cosmo­log­i­cal tools in the local universe.

I will also study a selected group of RR Lyrae stars in the outskirts of our Galaxy, which will provide strong constrains of the Galac­tic accre­tion history, and its mass. This will involve using propri­etary spectra of RR Lyrae to deter­mine their kinemat­ics (radial veloc­i­ties) and chemi­cal compo­si­tions. With this I will study their origin and possi­ble connec­tion with Galac­tic substruc­tures, laying the ground­work for future research in the era of large sky surveys.

Enthüllung der Geschichte der Galaxie anhand von pulsationsveränderlichen Sternen

Result of a member­ship deter­mi­na­tion of the stars, includ­ing the cepheid S Normae, to the cluster NGC 6087 using kinematic proper­ties based on Gaia-DR2 proper motions and parallaxes.

Gustavo Medina Toledo

Univer­sity of Heidelberg

Super­vised by

Prof. Dr.

Eva Grebel


Hector Fellow since 2014Disziplinen Eva Grebel