Interferometric and spectroscopic observations of the BRITE target Delta Cep

TL;DR

This paper combines interferometric and spectroscopic data with hydrodynamical modeling to refine the projection factor of Delta Cep and understand atmospheric velocity gradients in Cepheid variables.

Contribution

It introduces a hydrodynamical model to directly measure atmospheric velocity gradients and semi-theoretically determine correction factors for Cepheid pulsations.

Findings

Refined the projection factor of Delta Cep.

Measured the atmospheric velocity gradient contribution.

Calculated correction factors using hydrodynamical models.

Abstract

We used new HARPS-N spectra to revisitate the projection factor of Delta Cep and to directly measure the specific contribution of the velocity gradient within the atmosphere. By introducing an hydrodynamical model we could also determine the semi-theoretical values of the correction factor between the gas movement and the optical continuum by assuming radiative transfer in plane-parallel or sherically symmetric geometries, respectively.