Dwarfs or Giants? Stellar Metallicities and Distances from ugrizG Multiband Photometry

Abstract

We present a new fully data-driven algorithm that uses photometric data from the Canada-France-Imaging-Survey (CFIS; u), Pan-STARRS 1 (PS1; griz), and Gaia (G) to discriminate between dwarf and giant stars and to estimate their distances and metallicities. The algorithm is trained and tested using the SDSS/SEGUE spectroscopic dataset and Gaia photometric/astrometric dataset. At [Fe/H]< −1.2, the algorithm succeeds in identifying more than 70% of the giants in the training/test set, with a dwarf contamination fraction below 30% (with respect to the SDSS/SEGUE dataset). The photometric metallicity estimates have uncertainties better than 0.2 dex when compared with the spectroscopic measurements. The distances estimated by the algorithm are valid out to a distance of at least ∼ 80 kpc without requiring any prior on the stellar distribution, and have fully independent uncertainities that take into account both random and systematic errors. These advances allow us to estimate these stellar parameters for approximately 12 million stars in the photometric dataset. This will enable studies involving the chemical mapping of the distant outer disc and the stellar halo, including their kinematics using the Gaia proper motions. This type of algorithm can be applied in the Southern hemisphere to the first release of LSST data, thus providing an almost complete view of the external components of our Galaxy out to at least ∼ 80 kpc. Critical to the success of these efforts will be ensuring well-defined spectroscopic training sets that sample a broad range of stellar parameters with minimal biases. A catalogue containing the training/test set and all relevant parameters within the public footprint of CFIS is available online.

Photo-astrometric distances, extinctions, and astrophysical parameters for Gaia DR2 stars brighter than G = 18

“…Although methods explicitly tailored to detect metal-poor star candidates from combined broad-and narrow-band colours can be expected to perform much better (e.g. Beers et al 1985;Youakim et al 2017;Da Costa et al 2019;Thomas et al 2019;Arentsen et al 2020;Chiti et al 2021;Huang et al 2021a), our approach yields a large number of metal-poor star candidates for possible follow-up observations with multi-object spectroscopic surveys such as 4MOST (de Jong et al 2019;Chiappini et al 2019;Helmi et al 2019). The two top panels (showing Aitoff projections of the sky in ecliptic coordinates) highlight the long tidal tails of the Sagittarius dSph galaxy, also called the Sgr stream (e.g.…”

Photo-astrometric distances, extinctions, and astrophysical parameters for Gaia EDR3 stars brighter than G = 18.5

“…Although methods explicitly tailored to detect metal-poor star candidates from combined broad-and narrow-band colours can be expected to perform much better (e.g. Beers et al 1985;Youakim et al 2017;Da Costa et al 2019;Thomas et al 2019;Arentsen et al 2020;Chiti et al 2021;Huang et al 2021a), our approach yields a large number of metal-poor star candidates for possible follow-up observations with multi-object spectroscopic surveys such as 4MOST (de Jong et al 2019;Chiappini et al 2019;Helmi et al 2019). The two top panels (showing Aitoff projections of the sky in ecliptic coordinates) highlight the long tidal tails of the Sgr dSph galaxy, also called the Sgr stream (e.g.…”

The Mass and Age Distribution of Halo White Dwarfs in the Canada-France Imaging Survey

“…Given that half of our sample have masses consistent with a thin disk origin, it is useful to first check whether their kinematics could be consistent with such a population. We use the dwarf/giant catalogue presented in Thomas et al (2019) combined with radial velocities from LAMOST (Cui et al 2012;Zhao et al 2012) as a reference catalog for other disk and halo stars. We use this information to calculate the 3D velocities in spherical coordinates and present them in Figure 12 as the black contours.…”