Binary Cepheids from optical interferometry

¹ Universidad de Concepción, Departamento de Astronomía, Casilla 160-C, Concepción, Chile
² LESIA, Observatoire de Paris, CNRS UMR 8109, UPMC, Université Paris Diderot, 5 place Jules Janssen, 92195 Meudon, France
³ European Southern Observatory, Alonso de Córdova 3107, Casilla 19001, Santiago 19, Chile
⁴ Astronomy Department, University of Michigan, 1034 Dennison Bldg, Ann Arbor, MI 48109-1090, USA
⁵ Warsaw University Observatory, Al. Ujazdowskie 4, 00-478 Warsaw, Poland

Abstract

Classical Cepheid stars have been considered since more than a century as reliable tools to estimate distances in the universe thanks to their Period-Luminosity (P-L) relationship. Moreover, they are also powerful astrophysical laboratories, providing fundamental clues for studying the pulsation and evolution of intermediate-mass stars. When in binary systems, we can investigate the age and evolution of the Cepheid, estimate the mass and distance, and constrain theoretical models. However, most of the companions are located too close to the Cepheid (∼1–40 mas) to be spatially resolved with a 10-meter class telescope. The only way to spatially resolve such systems is to use long-baseline interferometry. Recently, we have started a unique and long-term interferometric program that aims at detecting and characterizing physical parameters of the Cepheid companions, with as main objectives the determination of accurate masses and geometric distances.