Cause of CHARA MIRC-X visibility discrepancies on E2 baseline

Determine the definitive cause of the intermittent discrepant uncalibrated visibilities observed on CHARA Array MIRC-X baselines including telescope E2 during the April 2021 observations of Polaris, discriminating between potential sources such as E2 delay line cart vibrations at very low tracking speeds and telescope oscillations while pointing near the pole.

Background

During CHARA/MIRC-X observations, the authors observed occasional offsets and excess scatter in uncalibrated visibilities, especially on baselines involving telescope E2 in April 2021. These anomalies appeared between different calibrators and sometimes within a single target data set, often after a brief pause to realign starlight into the fibers.

Despite inspection of the transfer functions and rejection of clearly discrepant data, the root cause remained unidentified. The authors suggest possible instrumental or mechanical origins, including delay line cart vibrations or telescope oscillations near the pole, but emphasize that the definitive cause has not been established.