  We present an overview of the Specific Objects Study (SOS) pipeline developed
within the Coordination Unit 7 (CU7) of the Gaia Data Processing and Analysis
Consortium (DPAC), the coordination unit charged with the processing and
analysis of variable sources observed by Gaia, to validate and fully
characterise Cepheids and RR Lyrae stars observed by the spacecraft. We
describe how the SOS for Cepheids and RR Lyrae stars (SOS Cep&RRL) was
specifically tailored to analyse Gaia's G-band photometric time-series with a
South Ecliptic Pole (SEP) footprint, which covers an external region of the
Large Magellanic Cloud (LMC). G-band time-series photometry and
characterization by the SOS Cep&RRL pipeline (mean magnitude and pulsation
characteristics) are published in Gaia Data Release 1 (Gaia DR1) for a total
sample of 3,194 variable stars, 599 Cepheids and 2,595 RR Lyrae stars, of which
386 (43 Cepheids and 343 RR Lyrae stars) are new discoveries by Gaia. All 3,194
stars are distributed over an area extending 38 degrees on either side from a
point offset from the centre of the LMC by about 3 degrees to the north and 4
degrees to the east. The vast majority, but not all, are located within the
LMC. The published sample also includes a few bright RR Lyrae stars that trace
the outer halo of the Milky Way in front of the LMC.
