# Gaia's Cepheids and RR Lyrae Stars and Luminosity Calibrations Based on Tycho-Gaia Astrometric Solution

## TL;DR

This paper utilizes Gaia DR1 parallaxes and multi-band photometry to calibrate key luminosity relations for Cepheids and RR Lyrae stars, improving distance measurement accuracy in astronomy.

## Contribution

It presents new calibrations of Period-Luminosity and related relations for Cepheids and RR Lyrae stars using Gaia TGAS data and various fitting techniques.

## Key findings

- Calibrated zero points for Cepheid and RR Lyrae luminosity relations.
- Compared different fitting methods in parallax and magnitude space.
- Enhanced precision in stellar distance measurements.

## Abstract

Gaia Data Release 1 contains parallaxes for more than 700 Galactic Cepheids and RR Lyrae stars, computed as part of the Tycho-Gaia Astrometric Solution (TGAS). We have used TGAS parallaxes, along with literature ($V, I, J, {K_\mathrm{s}}, W_1$) photometry and spectroscopy, to calibrate the zero point of the Period-Luminosity and Period-Wesenheit relations of classical and type II Cepheids, and the near-infrared Period-Luminosity, Period-Luminosity-Metallicity and optical Luminosity-Metallicity relations of RR Lyrae stars. In this contribution we briefly summarise results obtained by fitting these basic relations adopting different techniques that operate either in parallax or distance (absolute magnitude) space.