Calibrating the surface brightness – color relation for late-type red giants stars in the visible domain using VEGA/CHARA interferometric observations

¹ Université Côte d’Azur, Observatoire de la Côte d’Azur, CNRS, Laboratoire Lagrange, France
e-mail: Nicolas.Nardetto@oca.eu
² Univ. Grenoble Alpes, CNRS, IPAG, 38000 Grenoble, France
³ Departamento de Astronomía, Universidad de Concepción, Casilla 160-C, Concepción, Chile
⁴ Nicolaus Copernicus Astronomical Center, Polish Academy of Sciences, ul. Bartycka 18, 00-716 Warszawa, Poland
⁵ Unidad Mixta Internacional Franco-Chilena de Astronomía (CNRS UMI 3386), Departamento de Astronomía, Universidad de Chile, Camino El Observatorio 1515, Las Condes, Santiago, Chile
⁶ European Southern Observatory, Alonso de Córdova 3107, Casilla 19001, Santiago 19, Chile
⁷ LESIA (UMR 8109), Observatoire de Paris, PSL, CNRS, UPMC, Univ. Paris-Diderot, 5 place Jules Janssen, 92195 Meudon, France
⁸ Osservatorio Astronomico di Brera, Via E. Bianchi 46, 23807 Merate, Italy
⁹ Université de Lyon, Université Lyon 1, Ecole Normale Supérieure de Lyon, CNRS, Centre de Recherche Astrophysique de Lyon UMR5574, 69230, Saint-Genis-Laval, France
¹⁰ Georgia State University, PO Box 3969, Atlanta GA 30302-3969, USA
¹¹ CHARA Array, Mount Wilson Observatory, 91023 Mount Wilson CA, USA

Received: 7 February 2020
Accepted: 14 May 2020

Abstract

Context. The surface brightness – color relationship (SBCR) is a poweful tool for determining the angular diameter of stars from photometry. It was for instance used to derive the distance of eclipsing binaries in the Large Magellanic Cloud (LMC), which led to its distance determination with an accuracy of 1%.

Aims. We calibrate the SBCR for red giant stars in the 2.1 ≤ V − K ≤ 2.5 color range using homogeneous VEGA/CHARA interferometric data secured in the visible domain, and compare it to the relation based on infrared interferometric observations, which were used to derive the distance to the LMC.

Methods. Observations of eight G–K giants were obtained with the VEGA/CHARA instrument. The derived limb-darkened angular diameters were combined with a homogeneous set of infrared magnitudes in order to constrain the SBCR.

Results. The average precision we obtain on the limb-darkened angular diameters of the eight stars in our sample is 2.4%. For the four stars in common observed by both VEGA/CHARA and PIONIER/VLTI, we find a 1σ agreement for the angular diameters. The SBCR we obtain in the visible has a dispersion of 0.04 magnitude and is consistent with the one derived in the infrared (0.018 magnitude).

Conclusions. The consistency of the infrared and visible angular diameters and SBCR reinforces the result of 1% precision and accuracy recently achieved on the distance of the LMC using the eclipsing-binary technique. It also indicates that it is possible to combine interferometric observations at different wavelengths when the SBCR is calibrated.