RR Lyrae stars as standard candles in the Gaia Data Release 2 Era

Understand

We present results from the analysis of 401 RR Lyrae stars (RRLs) belonging to the field of the Milky Way (MW).

• For a fraction of them multi-band ($V$, $K_{\rm s}$, $W1$) photometry, metal abundances, extinction values and pulsation periods are available in the literature and accurate trigonometric parallaxes measured by the Gaia mission alongside Gaia $G$-band time-series photometry have become available with the Gaia second data release (DR2) on 2018 April 25.
• Using a Bayesian fitting approach we derive new near-, mid-infrared period-absolute magnitude-metallicity ($PMZ$) relations and new absolute magnitude-metallicity relations in the visual ($M_V - {\rm [Fe/H]}$) and $G$ bands ($M_G - {\rm [Fe/H]}$), based on the Gaia DR2 parallaxes.
• We find the dependence of luminosity on metallicity to be higher than usually found in the literature, irrespective of the passband considered.