From the inner to outer Milky Way: a photometric sample of 2.6 million red clump stars

Large pristine samples of red clump stars are highly sought after given that they are standard candles and give precise distances even at large distances. However, it is difficult to cleanly select red clumps stars because they can have the same T-eff and log g as red giant branch stars. Recently, it was shown that the asteroseismic parameters, Delta P and Delta v, which are used to accurately select red clump stars, can be derived from spectra using the change in the surface carbon to nitrogen ratio ([C/N]) caused by mixing during the red giant branch. This change in [C/N] can also impact the spectral energy distribution. In this study, we predict the Delta P, Delta v, T-eff, and log g using 2MASS, AIIWISE, Gaia, and Pan-STARRS data in order to select a clean sample of red clump stars. We achieve a contamination rate of similar to 20 per cent, equivalent to what is achieved when selecting from T-eff and log g derived from low-resolution spectra. Finally, we present two red clump samples. One sample has a contamination rate of similar to 20 per cent and similar to 405 000 red clump stars. The other has a contamination of similar to 33 per cent and similar to 2.6 million red clump stars that includes similar to 75 000 stars at distances >10 kpc. For vertical bar b vertical bar > 30 deg, we find 15 000 stars with contamination rate of similar to 9 per cent. The scientific potential of this catalogue for studying the structure and formation history of the Galaxy is vast, given that it includes millions of precise distances to stars in the inner bulge and distant halo where astrometric distances are imprecise.