Optical interferometry and Gaia parallaxes for a robust calibration of the Cepheid distance scale

TL;DR

This paper introduces the SPIPS modeling tool that combines multiple observational techniques, including Gaia parallaxes, to improve the calibration of the Cepheid distance scale and extend its applicability to distant Cepheids.

Contribution

The development of the SPIPS model integrating optical interferometry, radial velocities, photometry, and Gaia data for robust Cepheid calibration is a novel approach.

Findings

SPIPS enables precise projection factor calibration.

Application to RS Pup demonstrates model effectiveness.

Gaia parallaxes improve Cepheid distance measurements.

Abstract

We present the modeling tool we developed to incorporate multi-technique observations of Cepheids in a single pulsation model: the Spectro-Photo-Interferometry of Pulsating Stars (SPIPS). The combination of angular diameters from optical interferometry, radial velocities and photometry with the coming Gaia DR2 parallaxes of nearby Galactic Cepheids will soon enable us to calibrate the projection factor of the classical Parallax-of-Pulsation method. This will extend its applicability to Cepheids too distant for accurate Gaia parallax measurements, and allow us to precisely calibrate the Leavitt law's zero point. As an example application, we present the SPIPS model of the long-period Cepheid RS Pup that provides a measurement of its projection factor, using the independent distance estimated from its light echoes.