GaiaData Release 3

Abstract

Gaia Data Release 3 provides novel flux-calibrated low-resolution spectrophotometry for 220 million sources in the wavelength range 330 nm ≤ λ ≤ 1050 nm (XP spectra). Synthetic photometry directly tied to a flux in physical units can be obtained from these spectra for any passband fully enclosed in this wavelength range. We describe how synthetic photometry can be obtained from XP spectra, illustrating the performance that can be achieved under a range of different conditions -for example passband width and wavelength range-as well as the limits and the problems affecting it. Existing top-quality photometry can be reproduced within a few per cent over a wide range of magnitudes and colour, for wide and medium bands, and with up to millimag accuracy when synthetic photometry is standardised with respect to these external sources. Some examples of potential scientific application are presented, including the detection of multiple populations in globular clusters, the estimation of metallicity extended to the very metal-poor regime, and the classification of white dwarfs. A catalogue providing standardised photometry for 2.2 × 10 8 sources in several wide bands of widely used photometric systems is provided (Gaia Synthetic Photometry Catalogue; GSPC) as well as a catalogue of 10 5 white dwarfs with DA/non-DA classification obtained with a Random Forest algorithm (Gaia Synthetic Photometry Catalogue for White Dwarfs; GSPC-WD).

GaiaData Release 3

“…Red curves represent the median (P 50 ) of the distributions. Residuals as a function of G magnitude reveal a magnitude-dependent term at the faint end (at G 16): as discussed by Montegriffo et al (2022a), this trend in residuals is interpreted as the result of a systematic overestimation of background in Gaia BP and RP spectra, which causes the actual BP and RP fluxes to be slightly underestimated. This effect was already revealed by Evans et al (2018) by their comparison between Gaia DR2 photometry and external data, where the hockey stick term was first used to describe the observed feature, and by Riello et al (2021), who compared G-band photometry and synthetic G photometry computed on ECS (see their Fig.…”

“…The comparison with Hipparcos photometry demonstrates the excellent degree of spatial homogeneity of the synthetic photometry with a relative accuracy of less than 2.7 mmag over 90% of the entire sky. Additional validation by comparison with a large data set of reliable external photometry is provided in Montegriffo et al (2022a). Finally, caution must be exercised when using the spectra of very bright sources because ofv the presence of saturation, especially for sources brighter than G 4.…”

“…The availability of calibrated low-resolution SEDs means various applications are possible, such as performing wide-and medium-band synthetic photometry in any photometric system whose passbands are fully enclosed in the 330 − 1050 nm wavelength range covered by Gaia BP and RP spectra. The science verification paper by Montegriffo et al (2022a) is dedicated to this specific application. Here, we use this technique for the validation of our calibrations because it allows comparisons with completely independent reference data.…”

Reconciling astronomical distance scales with variable red giant stars

“…We collected V − and I−band photometric observations from OGLE -III (m I,OGLE , m V,OGLE ) photometric maps (for non-variable stars) and from published time-series of LPVs. We further collected G−band mean magnitudes, integrated G Rp spectrophotometry, and synthetic photometry in Johnson-Cousins (m V,syn and m I,syn ) and HST ACS/WFC magnitudes (m F606W,syn and m F814W,syn ) based on Gaia DR3 XP spectra [35,36], cf. Sect.…”

“…A.1. Specifically, we used the standardized Gaia synthetic magnitudes from table gaiadr3.source (labeled GSPC) and applied residual zero-point offsets determined by Montegriffo et al [36] with respect to photometric standards (∼ ±0.002 mag). We added the dispersion of the calibration checks (∼ 0.014 mag) to the photometric uncertainties in quadrature.…”