Gaia Data Release 2

Abstract

Context. The Gaia second Data Release (DR2) presents a first mapping of full-sky RR Lyrae stars and Cepheids observed by the spacecraft during the initial 22 months of science operations. Aims. The Specific Objects Study (SOS) pipeline, developed to validate and fully characterise Cepheids and RR Lyrae stars (SOS Cep&RRL) observed by Gaia, has been presented in the documentation and papers accompanying the Gaia first Data Release. Here we describe how the SOS pipeline was modified to allow for processing the Gaia multi-band (G, GBP, and GRP) time-series photometry of all-sky candidate variables and produce specific results for confirmed RR Lyrae stars and Cepheids that are published in the DR2 catalogue. Methods. The SOS Cep&RRL processing uses tools such as the period–amplitude and the period–luminosity relations in the G band. For the analysis of the Gaia DR2 candidates we also used tools based on the GBP and GRP photometry, such as the period–Wesenheit relation in (G, GRP). Results. Multi-band time-series photometry and characterisation by the SOS Cep&RRL pipeline are published in Gaia DR2 for 150 359 such variables (9575 classified as Cepheids and 140 784 as RR Lyrae stars) distributed throughout the sky. The sample includes variables in 87 globular clusters and 14 dwarf galaxies (the Magellanic Clouds, 5 classical and 7 ultra-faint dwarfs). To the best of our knowledge, as of 25 April 2018, the variability of 50 570 of these sources (350 Cepheids and 50 220 RR Lyrae stars) has not been reported before in the literature, therefore they are likely new discoveries by Gaia. An estimate of the interstellar absorption is published for 54 272 fundamental-mode RR Lyrae stars from a relation based on the G-band amplitude and the pulsation period. Metallicities derived from the Fourier parameters of the light curves are also released for 64 932 RR Lyrae stars and 3738 fundamental-mode classical Cepheids with periods shorter than 6.3 days.

Purveyors of fine halos

“…The brightest extratidal star (G = 15.8 mag) shares the same region as the locus of intratidal HB stars. In fact, both Abbas et al (2014) and Clementini et al (2019) list this star as being a pulsating RR Lyrae star of type ab. The former authors provide a distance estimate of 10.99 kpc, whichlacking a proper attached error margin on that value -is hard to compare with the cluster distance of 10.2 kpc, although an association seems feasible.…”

“…A few hundred stars in our analysis fall inside the fundamental mode RR Lyraes' instability strip boundaries provided by Clementini et al (2019), intrinsically making them candidates for possible variability. In order to investigate their periodic alternation, we retrieved their photometry from the time domain Catalina sky survey (CSS, Drake et al 2009).…”

“…7, but for M 3. The approximate color range of the instability strip from Clementini et al (2019) is indicated in the upper left panel by vertical dashed lines and the pulsating variable (see main text) is labeled "RRab". We note that the illustrated color and brightness for the RR Lyrae star are merely mean quantities, which may vary substantially over the pulsation cycle.…”

Probing the Galactic Halo with RR Lyrae Stars. I. The Catalog

“…In the near future, we plan to enlarge our sample by including data from additional spectroscopic surveys, e.g., the GALAH survey (De Silva et al 2015), as well as additional photometrically identified RRLs from the recent time-domain surveys, e.g. the Pan-STARRS1 (Chamber et al 2016;Sesar et al 2017); the Gaia DR2 (Clementini et al 2019). We expect to have precise measurements of metallicities, systemic radial velocities and distances of RRLs for the whole sky.…”

An Extended Theoretical Scenario for Classical Cepheids. I. Modeling Galactic Cepheids in the Gaia Photometric System

“…In this context, the Gaia mission (Gaia Collaboration et al 2016) is producing a 3D-map of 1 billion stars of the Milky Way with unprecedented accuracy. Focusing on pulsating stars, after the recent Data Release 2 (Gaia Collaboration et al 2018;Holl et al 2018), a large sample of Cepheids, observed in three photometric bands (G, G BP and G RP ) complemented with accurate parallaxes and proper motions, is available to the scientific community (Clementini et al 2019;Ripepi et al 2019), and the future releases will provide also radial velocity time series. This important database represents a challenging benchmark for testing the physical and numerical assumptions of current pulsation models.…”