The Gaia-Asas-Sn Classical Cepheid Sample. I. Sample Selection

We present a well-defined and characterized all-sky sample of classical Cepheids in the Milky Way, obtained by combining two time-domain all-sky surveys: Gaia DR2 (Gaia Collaboration et al. 2018) and All-Sky Automated Survey for Supernovae (ASAS-SN; Shappee et al. 2014). We first use parallax and variability information from Gaia to select similar to 30,000 bright (G < 17) Cepheid candidates with M-K < - 1. We then analyze their ASAS-SN V-band light curves, determining periods and classifying the light curves using their Fourier parameters. This results in similar to 1900 likely Galactic Cepheids, which we estimate to be greater than or similar to 90% complete and pure within our adopted selection criteria. This is the largest all-sky sample of Milky Way Cepheids that has such a well-characterized selection function, needed for population modeling and for systematic spectroscopic follow-up foreseen with Sloan Digital Sky Survey-V. About 130 of these potential Cepheids have not been documented in the literature even as possible candidates.