https://arxiv.org/abs/1811.05301

Abstract: The source detection sensitivity of Gaia is reduced near sources. To characterise this contrast sensitivity is important for understanding the completeness of the Gaia data products, in particular when evaluating source confusion in less well resolved surveys, such as in photometric monitoring for transits. Here, we statistically evaluate the catalog source density to determine the Gaia Data Release 2 source detection sensitivity as a function of angular separation and brightness ratio from a bright source. The contrast sensitivity from 0.4 arcsec out to 12 arcsec ranges in DG = 0-14 mag. We find the derived contrast sensitivity to be robust with respect to target brightness, colour, source density, and Gaia scan coverage.

https://arxiv.org/abs/1811.04302

The nearest extreme velocity stars among Gaia DR2 high proper motion stars

Among about 1.8 million Gaia DR2 high proper motion stars with μ>60 mas/yr and moderately significant parallaxes (ϖ>3σϖ), we have selected 109 high-speed star candidates with Galactic rest frame tangential velocities (corrected for solar motion) vt,g>700 km/s, well above the local Galactic escape velocity. After applying various Gaia DR2 astrometric quality criteria, only 39 candidates remained, including all three hypervelocity runaway white dwarfs (HVR WDs) found by Shen et al. (2018) but no additional such candidates (falling in the same region of the colour-magnitude diagram).

https://arxiv.org/abs/1810.09489

OGLE Collection of Galactic Cepheids

We present here a new major part of the OGLE Collection of Variable Stars - OGLE Collection of Galactic Cepheids. The new dataset was extracted from the Galaxy Variability Survey images - a dedicated large-scale survey of the Galactic disk and outer bulge conducted by the OGLE project since 2013.
The OGLE collection contains 2718 Cepheids of all types - classical, type II and anomalous. It more than doubles the number of known Galactic classical Cepheids. Due to the long-term monitoring and large number of epochs the selected sample is very pure, generally free from contaminating stars of other types often mimicking Cepheids. Its completeness is high at 90% level for classical Cepheids - tested using recent samples of Galactic Cepheids: ASAS-SN, ATLAS, Gaia DR2 and Wise catalog of variable stars. Our comparisons indicate that the completeness of the two latter datasets, Gaia DR2 and Wise catalog, is very low, at < 10% level in the magnitude range of the OGLE GVS survey (10.8 < I < 19.5 mag). Both these samples are severely contaminated by non-Cepheids (the purity is 67% and 56%, respectively).
We also present several interesting objects found in the new OGLE Collection - multi-mode pulsators, a first Galactic candidate for eclipsing system containing Cepheid, a binary Cepheid candidate.

https://arxiv.org/abs/1805.02079

Gaia Data Release 2: Specific characterisation and validation of all-sky Cepheids and RR Lyrae stars

Multiband time series photometry and characterisation by the SOS Cep&RRL pipeline are published in Gaia DR2 for 150,359 such variables (9,575 classified as Cepheids and 140,784 as RR Lyrae stars) distributed all over the sky. The sample includes variables in 87 globular clusters and 14 dwarf galaxies. To the best of our knowledge, as of 25 April 2018, variability of 50,570 of these sources (350 Cepheids and 50,220 RR Lyrae stars) is not known in the literature, hence likely they are 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 3,738 fundamental-mode classical Cepheids with period shorter than 6.3 days.

https://arxiv.org/abs/1805.02035

Gaia Data Release 2: The first Gaia catalogue of long-period variable candidates

Gaia DR2 provides a unique all-sky catalogue of 550'737 variable stars, of which 151'761 are long-period variable (LPV) candidates with G variability amplitudes larger than 0.2 mag (5-95% quantile range). About one-fifth of the LPV candidates are Mira candidates, the majority of the rest are semi-regular variable candidates. For each source, G, BP , and RP photometric time-series are published, together with some LPV-specific attributes for the subset of 89'617 candidates with periods in G longer than 60 days.

https://arxiv.org/abs/1804.09365

Gaia DR2 contains celestial positions and the apparent brightness in G for approximately 1.7 billion sources. For 1.3 billion of those sources, parallaxes and proper motions are in addition available. The sample of sources for which variability information is provided is expanded to 0.5 million stars.