Precise calibration of the dependence of surface brightness–colour relations on colour and class for late-type stars

Abstract

Context. Surface brightness–colour relations (SBCRs) are used to derive the stellar angular diameters from photometric observations. They have various astrophysical applications, such as the distance determination of eclipsing binaries or the determination of exoplanet parameters. However, strong discrepancies between the SBCRs still exist in the literature, in particular for early and late-type stars. Aims. We aim to calibrate new SBCRs as a function of the spectral type and the luminosity class of the stars. Our goal is also to apply homogeneous criteria to the selection of the reference stars and in view of compiling an exhaustive and up-to-date list of interferometric late-type targets. Methods. We implemented criteria to select measurements in the JMMC Measured Diameters Catalog. We then applied additional criteria on the photometric measurements used to build the SBCRs, together with stellar characteristics diagnostics. Results. We built SBCRs for F5/K7–II/III, F5/K7–IV/V, M–II/III and M–V stars, with respective rms of σFV = 0.0022 mag, σFV = 0.0044 mag, σFV = 0.0046 mag, and σFV = 0.0038 mag. This results in a precision on the angular diameter of 1.0%, 2.0%, 2.1%, and 1.7%, respectively. These relations cover a large V − K colour range of magnitude, from 1 to 7.5. Our work demonstrates that SBCRs are significantly dependent on the spectral type and the luminosity class of the star. Through a new set of interferometric measurements, we demonstrate the critical importance of the selection criteria proposed for the calibration of SBCR. Finally, using the Gaia photometry for our samples, we obtained (G − K) SBCRs with a precision on the angular diameter between 1.1% and 2.4%. Conclusions. By adopting a refined and homogeneous methodology, we show that the spectral type and the class of the star should be considered when applying an SBCR. This is particularly important in the context of PLATO.

The surface brightness–colour relations based on eclipsing binary stars and calibrated withGaiaEDR3

“…In Fig. 9 we plot our fit and a few calibrations based on interferometric measurements of stellar angular diameters (Kervella et al 2004;Challouf et al 2014;Boyajian et al 2014;Salsi et al 2020). The calibrations based on the interferometry have precision of about 2-3% for dwarfs in the colour range of our sample.…”

The SAPP pipeline for the determination of stellar abundances and atmospheric parameters of stars in the core program of the PLATO mission

“…Many SBCRs exist in the literature, but all of them are empirical and are calibrated on interferometric measurements (see Nardetto 2018 andSalsi et al 2020 for a short review) or on Galactic eclipsing binaries (Graczyk et al 2017(Graczyk et al , 2019. For example, Pietrzyński et al (2019) derived the distance to the Large Magellanic Cloud with a precision of 1 % using eclipsing binaries as distance indicators.…”

“…A 0.03 mag error in the K band magnitude causes an 80 K uncertainty in T eff and a 2 % uncertainty on the radius. The results also depend on the spectral type and luminosity class (Salsi et al 2020). Additionally, the method cannot be used for stars that show a significant activity level, have a companion(s), are flattened due to rotation (Challouf et al 2014(Challouf et al , 2015, and show signatures of wind and/or circumstellar shells.…”

“…In this work, we employ the SBCR relationships from Salsi et al ( 2021), which were derived for F5-K7 IV/V stars using the methodology described in Salsi et al (2020). The relationships are based on a careful selection of the interferometric data, suitable sample selection (no activity), and a homogeneous set of 2MASS photometry.…”

Precise calibration of the dependence of surface brightness–colour relations on colour and class for late-type stars (Corrigendum)

“…In the original paper, Salsi et al (2020), there is a mistake in the calculation of the uncertainty on the angular diameter estimate. Equation (8) should be written as follows:…”