Exploiting the Gaia EDR3 photometry to derive stellar temperatures

¹ Dipartimento di Fisica e Astronomia Augusto Righi, Università degli Studi di Bologna, Via Gobetti 93/2, 40129 Bologna, Italy
e-mail: alessio.mucciarelli2@unibo.it
² INAF – Osservatorio di Astrofisica e Scienza dello Spazio di Bologna, Via Gobetti 93/3, 40129 Bologna, Italy
³ University of Groningen, Kapteyn Astronomical Institute, 9747 AD Groningen, The Netherlands

Received: 1 April 2021
Accepted: 3 June 2021

Abstract

We present new colour–effective temperature (T_eff) transformations based on the photometry of the early third data release (EDR3) of the ESA/Gaia mission. These relations are calibrated on a sample of about 600 dwarf and giant stars for which T_eff has previously been determined with the infrared flux method from dereddened colours. The 1σ dispersion of the transformations is of 60–80 K for the pure Gaia colours (BP−RP)₀, (BP−G)₀, and (G−RP)₀, improving to 40–60 K for colours including the 2MASS K_s-band, namely (BP−K_s)0, (RP−K_s)₀, and (G−K_s)₀. We validate these relations in the most challenging case of dense stellar fields, where the Gaia EDR3 photometry could be less reliable, providing guidance for the safe use of Gaia colours in crowded environments. We compare the T_eff from the Gaia EDR3 colours with those obtained from standard (V−K_s)₀ colours for stars in three Galactic globular clusters of different metallicity, namely NGC 104, NGC 6752, and NGC 7099. The agreement between the two estimates of T_eff is excellent, with mean differences of between –50 and +50 K, depending on the colour, and with 1σ dispersions around the mean T_eff differences of 25–50 K for most of the colours and below 10 K for (BP−K_s)₀ and (G−K_s)₀. This demonstrates that these colours are analogous to (V−K_s)₀ as T_eff indicators.