MIRC closure phase studies for high precision measurements

To date, about 17 hot Jupiters have been directly detected by photometric and/or spectroscopic observations. Only 2 of them, however, are non-transiting hot Jupiters and the rest are all transiting ones. Since non-transiting hot Jupiter systems are analogs of high contrast binaries, optical/infrared long baseline interferometers can resolve them and detect the planets if highly stable and precise closure phase measurements are obtained. Thus, this is a good opportunity for optical/infrared interferometers to contribute to the field of exoplanet characterization. To reach this goal, detailed calibration studies are essential. In this paper, we report the first results of our closure phase calibration studies. Specifically, we find strong closure phase drifts that are highly correlated with target positions, i.e., altitude and azimuth angle. The correlation is stronger with altitude. Our experiments indicate that the major cause of the drifts is probably longitudinal dispersion. We are able to find a strategy with multiple approaches to reduce this effect, and are able to model the closure phase drift with a quadratic function of both altitude and azimuth. We then use this model to calibrate the drifts, and test this new calibration scheme with the high contrast binary ε Per. Although we can find a better orbital solution with this new method, we have also found difficulties to interpret the orbit of ε Per, which may stem from possible mis-calibrations or the influence of the third component in the system. More investigations are definitely necessary to address this issue and to further confirm our calibration strategy.