Interferometric Survey of Stellar Parameters: Limb darkening study with the Pipeline for Interferometric Measurements of Stars

Abstract

Accurate and unbiased determination of stellar parameters is of importance in many astrophysical domains. We therefore present an improved method to estimate stellar parameters, based on interferometric observations and stellar atmosphere models, as well as spectroscopic and photometric data. We estimate he fundamental stellar parameters by fitting a model of intensity profiles to interferometric data over a large spectral window and combining them with spectroscopic and photometric observations as an additional constraint on the fitting. We present results obtained with this method using observations from the Center for High Angular Resolution Astronomy (CHARA) and archival data from the Very Large Telescope Interferometer (VLTI). Based on discrete grids of one-dimensional stellar atmosphere models, we have developed an algorithm that trains artificial neural networks (ANNs) to estimate the spectrum and intensity profile of a star over the three photometric bands: R, H, and K. ANNs cover effective temperatures (T_ ranging from 4500–7000 K for dwarf stars and 2500–8000 K for giant stars, with surface gravities (łog g) ranging from 3.0–5.0 dex and -0.5–3.5 dex, respectively, and 12 viewing angles. A ̧hi^2 minimisation algorithm based on trained functions permitted us to simultaneously fit the observational spectrum and interferometric complex visibilities. As a result, consistent and precise stellar parameters, such as teff, łogg, and angular diameter (þeta), can be estimated. We fitted ι Psc (F7V) and δ Ari (G9.5IIIb) observed with SPICA, MIRC-X, and MYSTIC at the CHARA Array and on archival data of α Cen A and B (G2V and K1V) from VLTI/PIONIER with the Pipeline for Interferometric Measurements of Stars. For angular diameter estimations, when fitting with a one-dimensional stellar atmosphere model, we reached a precision of 0.5%. For teff and radius, we obtained a precision of approximately 1%, while we obtained a precision of 5% for łogg. Through evolutionary models, we further show how these constraints can improve the mass and age determination, as they attain a precision of approximately 2% for mass and 5-10% for age. This paper demonstrates the first results from the model fitting approach using interferometric data from different instruments combined with spectroscopic observations.