Galactic Calibration of the Tip of the Red Giant Branch

Indications from Gaia data release 2 (DR2) are that the tip of the red giant branch (TRGB, a population II standard candle related to the helium flash in low mass stars) is close to -4 in absolute I magnitude in the Cousins photometric system. Our sample is high latitude southern stars from the thick disk and inner halo, and our result is consistent with longstanding findings from globular clusters, whose distances were calibrated with RR Lyrae stars. As the Gaia mission proceeds, there is every reason to think an accurate Galactic geometric calibration of TRGB will be a significant outcome.Comment: to appear in PAS

Globular Cluster Distances from RR Lyrae Stars

The most common methods to derive the distance to globular clusters using RR Lyrae variables are reviewed, with a special attention to those that have experienced significant improvement in the past few years. From the weighted average of these most recent determinations the absolute magnitude of the RR Lyrae stars at [Fe/H]=-1.5 is Mv = 0.59 +/- 0.03 mag, corresponding to a distance modulus for the LMC (m-M)o = 18.48 +/- 0.05.Comment: 19 pages, 2 Postscript figures, Latex, uses svmult.cls. To be published in ``Stellar Candles'', Lecture Notes in Physics (http://link.springer.de/series/lnpp) Text update in Sect. 2.2, 2.4 and Table

RR Lyrae stars in the Andromeda satellite galaxies

In this contribution we summarize results on the search for variable stars and the study of the resolved stellar populations in four dwarf spheroidal satellites of the Andromeda galaxy that we have observed with the Large Binocular Cameras (LBC) at the Large Binocular Telescope (LBT)

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

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. Running the adopted Bayesian model on a simulated dataset we show that the high metallicity dependence is not caused by the method, but likely arises from the actual distribution of the data and the presence of a zero-point offset in the Gaia parallaxes. We infer a zero-point offset of $-0.057$ mas, with the Gaia DR2 parallaxes being systematically smaller. We find the RR Lyrae absolute magnitude in the $V$, $G$, $K_{\rm s}$ and $W1$ bands at metallicity of [Fe/H]=$-1.5$ dex and period of P = 0.5238 days, based on Gaia DR2 parallaxes to be $M_V = 0.66\pm0.06$ mag, $M_G = 0.63\pm0.08$ mag, $M_{K_{\rm s}} = -0.37\pm0.11$ mag and $M_{W1} = -0.41\pm0.11$ mag, respectively.Comment: 18 pages, 21 figures, 4 tables. Accepted for publication in MNRA