Gaia Data Release 2

Abstract

Context. The second data release of the Gaia mission (DR2) includes an advance catalogue of variable stars. The classifications of these stars are based on sparse photometry from the first 22 months of the mission. Aims. We set out to investigate the purity and completeness of the all-sky Gaia classification results with the help of the continuous light curves of the observed targets from the Kepler and K2 missions, focusing specifically on RR Lyrae and Cepheid pulsators, outside the Galactic bulge region. Methods. We cross-matched the Gaia identifications with the observations collected by the Kepler space telescope. We inspected the light curves visually, then calculated the relative Fourier coefficients and period ratios for the single- and double-mode K2 RR Lyrae stars to further classify them. Results. We identified 1443 and 41 stars classified as RR Lyrae or Cepheid variables in Gaia DR2 in the targeted observations of the two missions and 263 more RR Lyre targets in the full-frame images (FFI) of the original mission. We provide the cross-match of these sources. We conclude that the RR Lyrae catalogue has a completeness between 70–78%, and provide a purity estimate of between 92 and 98% (targeted observations) with lower limits of 75% (FFI stars) and 51% (K2 worst-case scenario). The low number of Cepheids prevents us from drawing detailed conclusions, but the purity of the DR2 sample is estimated to be about 66%.

A catalogue of over 10 million variable source candidates in ZTF Data Release 1

“…Since the largest available homogeneous variable star candidate catalogue includes mainly periodic variables, we compared our catalogue with the GAIA-DR2 RR Lyrae variable candidates list (Gaia Collaboration 2018). Molnár et al (2018) estimated that this catalogue is 70 per cent-78 per cent complete, and has purity of 92 per cent to 98 per cent. The GAIA-DR2 RR Lyr catalogue contains about 56 000 RR Lyr candidates brighter than G mag of 20, and above Declination of −30 deg.…”

Gaia Data Release 2

“…15, generally confirming the expected trend that higher score thresholds increase the completeness to contamination ratio more efficiently than lower score limits. In addition to the SOS module results described in Clementini et al (2019) as part of the Gaia variability pipeline, an independent validation of the RR Lyrae classifications was performed with stars observed in selected K2 fields of the Kepler space telescope (Molnár et al 2018).…”

“…It generally confirms the expected trend that higher score thresholds increase the completeness-to-contamination ratio more efficiently than lower score limits. In addition to the SOS module results described in Clementini et al (2019) as part of the Gaia variability pipeline, an independent validation of a small sample of Cepheid classifications was performed with stars observed in selected K2 fields of the Kepler space telescope (Molnár et al 2018). The set of Gaia DR2 Cepheids in the SOS results has recently been reclassified (Ripepi et al 2019), providing a sample with negligible contamination and more accurate Cepheid subclassifications.…”

“…Belokurov et al 2017;Jacyszyn-Dobrzeniecka & the OGLE Team 2018). In addition to the classification scores and other indications given in this article, subsets of sources with enhanced reliability and sufficient sampling are selected by subsequent pipeline modules (SOS) for some of the variability types, whose detailed analyses and validations are presented in separate articles (Mowlavi et al 2018, for long-period variables, and Clementini et al 2019and Molnár et al 2018.…”

Empirical completeness assessment of the Gaia DR2, Pan-STARRS 1, and ASAS-SN-II RR Lyrae catalogues

“…Completeness rates of the RRLs identified in Gaia DR2 were estimated also in other works that validated such candidates. Molnár et al (2018) compared the RRL candidates in the Gaia DR2 classification (VC) with the ones found in a selection of fields of the Kepler and K2 missions (Borucki et al 2010;Howell et al 2014). These fields covered about 110 deg 2 each and were distributed along the Ecliptic (except for the original Kepler field); they spanned Galactic latitudes |b| < 70 • but excluded the region of the Galactic bulge (as already well resolved in Soszyński et al 2014).…”