Dual-field interferometry uses a bright reference star for real-time fringe tracking, allowing a second beam combiner to record long coherent integrations on a fainter off-axis science target. At the Center for High Angular Resolution Astronomy (CHARA) Array, we implement this mode using the six-telescope MIRC-X and MYSTIC beam combiners in the H and K bands, respectively. We first demonstrated this capability in summer 2025 on the hierarchical triple $\alpha$~Piscium. MIRC-X tracked component A in the $H$ band, while MYSTIC observed component B in the K band, resolving the 7~mas Ba--Bb subsystem and measuring the relative astrometry of the 1.85~arcsec A--B pair with an uncertainty of 234~$\mu$as. Here, we describe subsequent phase-tracking testing, preliminary sensitivity simulations, and planned instrumental upgrades aimed at extending this mode to faint off-axis science targets.
N. Anugu, J. Monnier, D. Gies et al.· Optical and Infrared Interfe...· 0 citations
Estimations of stellar angular diameters can be determined based on the surface brightness-colour relation (SBCR) and photometry. In the context of the PLATO space mission, the SBCR is considered to be an independent empirical alternative for estimating the stellar radii of FGK stars.
We implemented a homogeneous approach, not only for calibrating the SBCR for FGK-IV/V stars, but also for determining their fundamental parameters. This made it possible to reliably place the stars on the Hertzsprung-Russell (HR) diagram and to study their impact on the SBC relations.
We performed interferometric observations of 18 quiescent FGK-IV/V stars in the Gaia magnitude range of . For the first time, we used three different interferometric instruments operating in the , , and bands to measure the polychromatic limb-darkened angular diameters. In parallel, by using public domain spectra, we were able to estimate the stellar parameters (T_ . 3.088 łeq G łeq 5.498 R H K łog g, and Z) by using the open Python tool iSpec
We achieved an average accuracy of 2.3% for the limb-darkened angular diameters based on polychromatic observations. However, we observed that our SBCR relation does not follow the calibration of the SBC relations in Gaia found in the literature. Furthermore, we found that the łog g and Z parameters have no impact on this relationship. Given the characteristics of our sample of quiescent stars, it constitutes an ideal set of targets for conducting a new SBCR calibration within the framework of the PLATO space mission. In this context, we report a SBCR calibration with σ_ RMS = 0.012, 0.009, and 0.009 in the G, G_ BP , and G_RP Gaia bands, respectively.
This work is part of a series of papers reporting the first results obtained using a polychromatic approach to measure angular diameters, employing a fully homogeneous methodology for determining the fundamental parameters of stars and measuring the limb-darkened angular diameters
R. I. Ibañez Bustos, D. Mourard, N. Nardetto et al.· Astronomy & Astrophysics· 0 citations
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