Determining the incidence rate of magnetic $δ$ Scuti candidates with CoRoT

Abstract

$δ$ Scuti stars are pulsating stars constituting the $δ$ Scuti instability strip in the Hertzsprung-Russell (HR) diagram, which consists of A and F stars. They are in the transition region between high-mass hot stars and low-mass solar-like stars, making understanding their magnetic properties essential to painting a complete picture of magnetism across the HR diagram. Also, discovering magnetic stars allows for magneto-asteroseismology, which can be used to determine the internal rotation profile, internal magnetic field strength, and the efficiency of mixing and transport processes more accurately than classical asteroseismology. To date, surface magnetic fields have been detected in 13 $δ$ Scuti stars. However, the overall incidence rate of magnetism in these stars remains unknown. Fossil magnetic fields are detected in 10% of OBA stars. We investigated the incidence rate of surface magnetic fields among $δ$ Scuti stars using photometric data from the CoRoT space mission. We analyzed long-duration light curves of $\sim$ 1750 $δ$ Scuti stars to search for rotational modulation - a photometric signature that indicates chemical or temperature spots at the stellar surface, usually caused by magnetic fields. We identified 147 rotational variables that we designate as magnetic candidates, thus potentially increasing the known population of magnetic $δ$ Scuti stars drastically and suggesting an incidence rate of fossil magnetic fields in $δ$ Scuti stars similar to the incidence rate in OBA stars in general. Our analysis also revealed a few $δ$ Scuti -- $γ$ Dor hybrid stars in the sample. We determined the rotation periods and projected rotation velocities of the magnetic candidates in order to select suitable targets for follow-up spectropolarimetric observations aimed at confirming and characterizing their magnetic fields.