Gaia Data Release 3

External calibration of BP/RP low-resolution spectroscopic data

¹ INAF – Osservatorio di Astrofisica e Scienza dello Spazio di Bologna, Via Gobetti 93/3, 40129 Bologna, Italy
² Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA, UK
³ Max-Planck-Institute for Astronomy, Königstuhl 17, 69117 Heidelberg, Germany
⁴ INAF – Osservatorio Astrofisico di Arcetri, Largo E. Fermi, 5, 50125 Firenze, Italy
⁵ Space Science Data Center – ASI, Via del Politecnico SNC, 00133 Roma, Italy
⁶ Institut de Ciències del Cosmos (ICC), Universitat de Barcelona (IEEC-UB), c/ Martí i Franquès, 1, 08028 Barcelona, Spain
⁷ INAF – Osservatorio Astronomico di Padova, Vicolo Osservatorio 5, 35122 Padova, Italy
⁸ INAF – Osservatorio Astronomico di Roma, Via Frascati 33, 00078 Monte Porzio Catone, Roma, Italy
⁹ School of Physics & Astronomy, University of Leicester, Leicester LE9 1UP, UK
¹⁰ Leiden Observatory, Leiden University, Niels Bohrweg 2, 2333 CA Leiden, The Netherlands
¹¹ Institute for Astronomy, School of Physics and Astronomy, University of Edinburgh, Royal Observatory, Blackford Hill, Edinburgh EH9 3HJ, UK
¹² INAF – Osservatorio Astronomico d’Abruzzo, Via Mentore Maggini, 64100 Teramo, Italy
¹³ Institut d’Astrophysique et de Géophysique, Université de Liège 19c, Allée du 6 Août, 4000 Liège, Belgium
¹⁴ Royal Observatory of Belgium, 3 Avenue Circulaire, 1180 Brussels, Belgium
¹⁵ Kavli Institute for Cosmology, Institute of Astronomy, Madingley Road, Cambridge CB3 0HA, UK
¹⁶ IAC – Instituto de Astrofisica de Canarias, Via Láctea s/n, 38200 La Laguna SC, Tenerife, Spain
¹⁷ Ruder Bošković Institute, Bijenička Cesta 54, Zagreb, Croatia
¹⁸ STFC, Rutherford Appleton Laboratory, Harwell, Didcot OX11 0QX, UK
¹⁹ Department of Artificial Intelligence, Universidad Nacional de Educación a Distancia, c/ Juan del Rosal 16, 28040 Madrid, Spain

Received: 27 April 2022
Accepted: 23 May 2022

Abstract

Context.Gaia Data Release 3 contains astrometry and photometry results for about 1.8 billion sources based on observations collected by the European Space Agency (ESA) Gaia satellite during the first 34 months of its operational phase (the same period covered by Gaia early Data Release 3; Gaia EDR3). Low-resolution spectra for 220 million sources are one of the important new data products included in this release.

Aims. In this paper, we focus on the external calibration of low-resolution spectroscopic content, describing the input data, algorithms, data processing, and the validation of the results. Particular attention is given to the quality of the data and to a number of features that users may need to take into account to make the best use of the catalogue.

Methods. We calibrated an instrument model to relate mean Gaia spectra to the corresponding spectral energy distributions (SEDs) using an extended set of calibrators: this includes modelling of the instrument dispersion relation, transmission, and line spread functions. Optimisation of the model is achieved through total least-squares regression, accounting for errors in Gaia and external spectra.

Results. The resulting instrument model can be used for forward modelling of Gaia spectra or for inverse modelling of externally calibrated spectra in absolute flux units.

Conclusions. The absolute calibration derived in this paper provides an essential ingredient for users of BP/RP spectra. It allows users to connect BP/RP spectra to absolute fluxes and physical wavelengths.