The Gaia grid of spectro-photometric standard stars

TL;DR

This paper reports on the development of a ground-based grid of about 200 spectro-photometric standard stars with 1% accuracy, designed to calibrate Gaia's data, with initial results showing promising accuracy and ongoing improvements.

Contribution

It introduces a new grid of spectro-photometric standards for Gaia calibration, detailing selection, monitoring, and initial results with high accuracy.

Findings

Achieved ~1% accuracy in flux calibration

Grid contains about half of the final sample

Candidates monitored for constancy within ±5 mmag

Abstract

We describe the preliminary results of a ground-based observing campaign aimed at building a grid of approximately 200 spectro-photometric standard stars (SPSS), with an internal $\simeq 1$\% accuracy (and sub-percent precision), tied to CALSPEC Vega and Sirius systems within $\simeq 1$\%, for the absolute flux calibration of data gathered by {\it Gaia}, the European Space Agency (ESA) astrometric mission. The criteria for the selection and a list of candidates are presented, together with a description of the survey's strategy and the adopted data analysis methods. All candidates were also monitored for constancy (within $\pm 5$ mmag, approximately). The present version of the grid contains about half of the final sample, it has already reached the target accuracy but the precision will substantially improve with future releases. It will be used to calibrate the {\it Gaia} (E)DR3 release of spectra and photometry.