Visibility Estimation for the CHARA/JouFLU Exozodi Survey

TL;DR

This paper presents improved methods for estimating and calibrating interferometric visibility in the CHARA/JouFLU exozodi survey, reducing bias and errors, especially for bright stars, with statistical validation.

Contribution

It introduces a median-based estimator for uncalibrated visibility and a calibration method that accounts for calibrator uncertainties and timing, enhancing accuracy over previous approaches.

Findings

Median estimator reduces bias compared to other estimators.

Calibration method decreases bias and errors, notably for bright stars.

Bias and error reduction can reach 20-40%, statistically significant at 95% CL.

Abstract

We discuss the estimation of the interferometric visibility (fringe contrast) for the exozodi survey conducted at the CHARA array with the JouFLU beam combiner. We investigate the use of the statistical median to estimate the uncalibrated visibility from an ensemble of fringe exposures. Under a broad range of operating conditions, numerical simulations indicate that this estimator has a smaller bias compared to other estimators. We also propose an improved method for calibrating visibilities, which not only takes into account the time-interval between observations of calibrators and science targets, but also the uncertainties of the calibrators' raw visibilities. We test our methods with data corresponding to stars that do not display the exozodi phenomenon. The results of our tests show that the proposed method yields smaller biases and errors. The relative reduction in bias and error is generally modest, but can be as high as $\sim 20-40\%$ for the brightest stars of the CHARA data, and statistically significant at the $95\%$ confidence level (CL).