Based on the success of four-telescope imaging with the Michigan Infrared Combiner (MIRC) on the CHARA
Array, our Michigan-based group will now upgrade our system to combine all six CHARA telescope simultaneously.
In order to make this observationally efficient, we have had to improve a number of subsystems and
commission new ones, including the new CHAMP fringe tracker, the introduction of photometric channels, the
upgrading of the realtime operating systems, and the obvious hardware and software upgrades of the control
system and the data pipeline. Here we will discuss the advantages of six-telescope operation, outline our upgrade
plans and discuss our current progress.
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.
Although direct direction of light from hot Jupiters has recently been achieved by measurements from the
Spitzer Space Telescope and the Hubble Space Telescope, information on those hot Jupiters are still not enough
to break all the model degeneracies and provide detailed conclusions. More detections that can measure the
astrometric orbits and flux variations of hot Jupiters, especially in the near-IR, are necessary. One promising
way to reach this goal is to use precision closure phase measurements obtained with ground-based long baseline
optical interferometers. Here we present our preliminary closure phase studies on the nearby hot Jupiter system
υ And b using CHARA-MIRC. Our data analysis shows our closure phase precisions are at ~ 0.4σ and ~ 0.6σ
level of the required signal for detections for the short and long triangles of CHARA respectively. In order to
make real detections, we have several improvements in the future to increase the signal-to-noise of the data. Once
these improvements are realized, our goal of directly detecting light from υ And b will be feasible to achieve.
We report the first scientific results from the Michigan Infrared Combiner (MIRC), including the first resolved
image of a main-sequence star besides the Sun. Using the CHARA Array, MIRC was able to clearly resolve the
well-known elongation of Altair's photosphere due to centrifugal distortion, and was also able to unambiguously
image the effect of gravity darkening. In this report, we also show preliminary images of the interacting binary
β Lyr and give an update of MIRC performance.
The Michigan Infrared Combiner (MIRC) has been designed for two primary goals: 1) imaging with all six CHARA telescopes simultaneously in the near-infrared, 2) direct detection of "hot Jupiter" exoplanets using precision closure phases. In September 2005, MIRC was commissioned on-sky at the CHARA Array on Mt. Wilson, CA, successfully combining light from 4 telescopes simultaneously. After a brief overview of MIRC features and design philosophy, we provide detailed description of key components and present results of laboratory tests. Lastly, we present first results from the commissioning run, focusing on engineering performance. We also present remarkable on-sky closure phase results from the first night of recorded data with the best-ever demonstrated closure phase stability and precision (ΔΦ = 0.03 degrees).
We present a formal comparison of the performance of algorithms used for synthesis imaging with optical/infrared long-baseline interferometers. Five different algorithms are evaluated based on their performance with simulated test data. Each set of test data is formatted in the OI-FITS format. The data are calibrated power spectra and bispectra measured with an array intended to be typical of existing imaging interferometers. The strengths and limitations of each algorithm are discussed.