Date: 3.11.2026

Felipe Espinoza (CAMK PAN,WAW)

Evolutionary Study of Classical Cepheids in Binary Systems

Abstract:
Classical Cepheids are pulsating stars whose period–luminosity relation makes them fundamental standard candles for the extragalactic distance scale. Their pulsation and evolution also provide stringent tests of stellar theory. Two aspects of their physics remain poorly constrained: the empirical location of the instability strip (IS) and their masses. In this presentation, I will show the empirical IS in the Large and Small Magellanic Clouds, determined using OGLE catalogs and precise reddening maps. Its edges reveal unexpected features that challenge current evolutionary models. To constrain Cepheid masses, I will present the q-PED method for estimating physical parameters of Cepheids in non-eclipsing double-lined binaries. Its first application points to a Cepheid that is most likely a merger product on its first crossing of the IS. I will then show how the method, extended to binary double Cepheids in the LMC, SMC, and Milky Way, pushes the empirical mass range of Cepheids into previously unexplored territory. These systems also hint that binary interactions may play a larger role in Cepheid evolution than commonly assumed. Together, these results provide new empirical benchmarks for models of intermediate-mass stellar evolution and pulsation.