The ongoing Gaia mission will undertake an astrometric, photometric and spectroscopic survey of the Galaxy. The Gaia consortium will use Gaia-only data to classify objects and to estimate their individual astrophysical parameters. However, one can achieve more reliable estimates of stellar parameters by combining Gaia data with data from other spectroscopic and photometric surveys.
The Gaia “hybrid catalog” project will provide an exquisite value-added catalogs of astrophysical parameters for Gaia targets by taking into account the “obvious” non-Gaia data (e.g., SDSS, WISE, Pan-STARRS, APOGEE, PPMXL, SDSS, 2MASS, Tycho). By including spectroscopic indicators of metallicity when available, or infrared photometry, we can reduce the degeneracies between extinction and temperature and improve the estimation of metallicity and surface gravity.
However, the creation of such catalogs comes with significant challenges. First the cross-matching of catalogs with various selection functions, or photometric depths. Second, we must optimize the data analysis to produce the most accurate information given a specific science goal. Finally, the construction of such catalogs will require significant computation power. The current plan is to do this using the local resources at the Max-Planck-Institut für Astronomie, and then each catalog will go through validation and integration processes to finally be released as part of the value-added Gaia data products. From these challenges, it is clear that hybrid catalogs will not be a copy of the Gaia catalog but must be adapted to support very specific science questions.
In the poster we presented, we details in particular two applications
of the Gaia hybrid catalogs. First, we considered the addition of WISE
data to the Gaia information. The WISE data enable us to constrain
not only the amount of extinction through the addition of infrared
data, but also allow us to better classify certain spectral types. For
instance, from the addition of the WISE filters, one can select the
Oxygen-rich Asymptotic Giant Branch (AGBs) stars to find spatial
substructures with particular interstellar medium properties. Breaking through the distance-extinction degeneracies will also help finding large
scale structures in the disk such as streams or spiral arms, especially
when combined with age or metallicity selections for instance.
Second, we presented one aspect of the hybrid catalogs dedicated
to support the analysis of star clusters. Star clusters are not only
calibrators of stellar evolution models but also references to study star
formation in general. We presented one future outcome of the hybrid
catalogs, in which we provide for known star clusters, an assessment of
stellar memberships based on a combination of phase-space, and colormagnitude
distribution fitting. In this application, the assumption that
a cluster is a “simple” population provides a significant advantage when
deriving individual star properties. Eventually one can imagine this
application can be extended to stellar streams.
Hybrid catalogs are meant to be provided along with the Gaia data
releases, and will offer a tremendous source of validation for the Gaia