Gaia data release 1: Principles of the photometric calibration of the G band

TL;DR

This paper details the calibration process of Gaia's G band photometry for Data Release 1, including models, methods, and results, establishing a foundation for precise stellar measurements in our galaxy.

Contribution

It introduces the calibration model and pipeline for Gaia G band photometry, linking it to absolute flux scales for the first data release.

Findings

Successful application of the calibration pipeline to DR1 data

Provision of absolute zero points and transformations to other systems

Identification of calibration elements and models used

Abstract

Context. Gaia is an ESA cornerstone mission launched on 19 December 2013 aiming to obtain the most complete and precise 3D map of our Galaxy by observing more than one billion sources. This paper is part of a series of documents explaining the data processing and its results for Gaia Data Release 1, focussing on the G band photometry. Aims. This paper describes the calibration model of the Gaia photometric passband for Gaia Data Release 1. Methods. The overall principle of splitting the process into internal and external calibrations is outlined. In the internal calibration, a self-consistent photometric system is generated. Then, the external calibration provides the link to the absolute photometric flux scales. Results. The Gaia photometric calibration pipeline explained here was applied to the first data release with good results. Details are given of the various calibration elements including the mathematical formulation of the models used and of the extraction and preparation of the required input parameters (e.g. colour terms). The external calibration in this first release provides the absolute zero point and photometric transformations from the Gaia G passband to other common photometric systems. Conclusions. This paper describes the photometric calibration implemented for the first Gaia data release and the instrumental effects taken into account. For this first release no aperture losses, radiation damage, and other second-order effects have not yet been implemented in the calibration.