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gaia data release 3 documentation

11.1 Introduction

11.1.1 Astrophysical parameters in Gaia DR3

Author(s): Orlagh L. Creevey, Ulrike Heiter, Frédéric Thévenin

Source characterisation in DR3, based on mean BP/RP and RVS spectra, astrometry and photometry, was performed by the coordination unit 8 (CU8), entitled Astrophysical Parameters. Characterisation implies stellar and extra-galactic class probabilities, object-type labels, and parametrisations with associated uncertainties. We refer to these as 1D data products. It also includes multi-dimensional (MD) data products such as a 2D extinction map and a self-organising map of outliers. All of these products, appearing in 538 unique fields, are found in one of 10 tables in the Gaia DR3 archive, with a subset of these also copied to gaia_source. A synthetic description of the contents of these tables is given in Table 11.1.

These products were produced by the CU8 Astrophysical Parameters Inference System (Apsis) chain which consists of 14 modules, see Section 11.1.2. In comparison, in Gaia DR2, only two modules produced five stellar parameters and uncertainties based on the integrated G, GBP, GRP photometry and astrometry (Teff, AG, E(GBP-GRP), , ), see Andrae et al. (2018). Creevey et al. (2023) presents the overall content of the archive produced by Apsis, while Fouesneau et al. (2023) and Delchambre et al. (2023) focus on the validation of the stellar and non-stellar content, respectively.

The 43 main 1D independent data products in Gaia DR3 comprise stellar atmospheric parameters (Teff, logg, [M/H], [α/Fe], activity index, vsini), binary component parameters (Teff 1, Teff 2, logg 1, logg 2), chemical abundances ([Fe/M], [Fe ii/M], [N/Fe], [Mg/Fe], [Si/Fe], [S/Fe], [Ca/Fe], [Ti/Fe], [Cr/Fe], [Ni/Fe], [Zr/Fe], [Ce/Fe], [Nd/Fe]), equivalent widths of Hα and of a CN line, stellar evolutionary parameters (, , , age, evolutionary stage, absolute G magnitude, gravitational redshift), interstellar medium characterisation parameters (extinction – monochromatic and in G, GBP, GRP bands, colour-excess, diffuse interstellar band characteristics) and distance, classification parameters (class labels from three different modules, class probabilities for 12 different classes from two modules, and a spectral type), quasar and galaxy redshifts, and information on each neuron in the self-organising map from the outlier analysis. Other 1D data products include auxiliary information such as quality flags, bolometric correction and goodness-of-fit indicators. We refer to all of these products collectively as astrophysical parameters (APs).

The MD data products comprise a 2D total galactic extinction map at four HEALPix levels and at the optimal HEALPix level, a table of outlier properties classified as neurons in a self-organising map and the corresponding BP/RP spectra, as well as Markov-Chain Monte Carlo (MCMC) samples for stellar parameters from two of the Apsis modules. An overview of the data products is given in Section 11.1.3.

Table 11.1: Gaia DR3 tables with astrophysical parameters from CU8.
type table name content description
Source-based astrophysical_parameters stellar parameters and source classification
astrophysical_parameters_supp stellar parameters from an alternative method,
data set, or specific library
qso_candidates quasar parameters and class probabilities
galaxy_candidates galaxy parameters and class probabilities
gaia_source subset of stellar parameters and class probabilities
Multi-dimensional oa_neuron_information Self-organising map (SOM) of outlier sources
oa_neuron_xp_spectra Prototype BP/RP spectra corresponding to each SOM neuron
total_galactic_extinction_map 2D extinction map at 4 HEALPix levels
total_galactic_extinction_map_opt 2D extinction map using optimal HEALPix level
mcmc_samples_gspphot MCMC samples from stellar parametriser GSP-Phot
mcmc_samples_msc MCMC samples from binary parametriser MSC