Single Baseline Phases in Optical Interferometry

Details Single Baseline Phases in Optical Interferometry Single Baseline Phases in Optical Interferometry

Dec 2006

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006aas...20917303j&link_type=abstract

2007 AAS/AAPT Joint Meeting, American Astronomical Society Meeting 209, #173.03; Bulletin of the American Astronomical Society,

Statistics

Scientific paper

One of the critical tasks ahead for optical interferometry is to improve the determination of parameters for astronomical objects. The SNR of the squared visibilities in marginal data can be greatly improved with coherent integration, but this helps only to a point: once the SNR exceeds some threshold, the accuracy is limited by calibration uncertainties rather than by photon statistics. The phase normally used in optical interferometry is the sum of the phases of the complex visibilities (the baseline phases) around a triangle of baselines. This closure phase is immune to all non-source effects, including the calibration effects that normally affect squared visibilities. However, only one closure phase is produced from the three baseline phases, and its uncertainty is worse than the uncertainty on the baseline phases. Additionally, the closure phase is only one phase determination whereas the corresponding baseline phases represent three separate phase measurements. We propose using the baseline phases to circumvent the limitations of squared visibilities and closure phases. Baseline phases are also immune to the normal calibration effects, so their SNR is entirely determined by photon statistics. Our approach is to coherently integrate [e.g., Jorgensen SPIE 2004, 2006, AJ 2005 (submitted)] to improve the SNR of the complex visibilities, and then to extract phases for single baselines. This technique depends on spectrally dispersing the fringes so the group delays can be determined. Unlike closure phases, baseline phases contain effects of the atmosphere, fringe-tracking errors, and internal instrument dispersion. We have shown that these effects can be measured and subtracted, leaving only the source phase. In this presentation we will demonstrate how to work with baseline phases and how they can used to model different sources and extract high-precision parameters.

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