24 July 2014 Progress toward unprecedented imaging of stellar surfaces with the Navy precision optical interferometer
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Abstract
We present progress on the stellar surface imaging project recently funded by the U. S. National Science Foun- dation. With the unique layout of the Navy Precision Optical Interferometer (NPOI) in combination with data acquisition and fringe-tracking upgrades we expect to be able to substantially exceed the imaging fidelity and resolution of any other interferometer in operation. The project combines several existing advances and infras- tructure at NPOI with modest enhancements. For optimal imaging there are several requirements that should be fulfilled. The observatory should be capable of measuring visibilities on a wide range of baseline lengths and orientations, providing complete Fourier (UV) coverage in a short period of time. It should measure visibility amplitudes with good SNR on all baselines as critical imaging information is often contained in low-amplitude visibilities. It should measure the visibility phase on all baselines. The technologies which can achieve this are the NPOI Y-shaped array with (nearly) equal spacing between telescopes and an ability for rapid configuration. Placing 6-telescopes in a row makes it possible to measure visibilities into the 4th lobe of the visibility function. By arranging the 12 available telescopes carefully we can switch, every few days, between 6 different 6-station chains which provide symmetric coverage in the Fourier plane without moving any telescopes, only by moving beam relay mirrors. The 6-station chains are important to achieve the highest imaging resolution, and switching rapidly between station chains provides uniform coverage. Coherent integration techniques can be used to obtain good SNR on very small visibilities. Coherently integrated visibilities can be used for imaging with standard radio imaging packages such as AIPS. The commissioning of one additional station, the use of new data acqui- sition hardware and fringe tracking algorithms are the enhancements which are making this project a reality. The New Classic data acquisition system, based on a powerful Stratix FPGA and fast Direct Memory Access module, upgrades the existing Classic beam combiner to allow for continuous data recording across all baselines available with 6 telescopes. It also provides the computing power and software environment necessary for im- plementing the 6-station, 5-baseline fringe-tracking algorithms. In separate papers we discuss the New Classic data acquisition system and the fringe-tracking algorithms in greater detail. In this paper we will focus on an overview of the project. We will describe the observation planning, logistics of the observations, and discuss the current status of the project including preliminary results and simulations of expected future results.
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A. M. Jorgensen, A. M. Jorgensen, D. Mozurkewich, D. Mozurkewich, H. R. Schmitt, H. R. Schmitt, G. T. van Belle, G. T. van Belle, D. J. Hutter, D. J. Hutter, J. Clark, J. Clark, J. T. Armstrong, J. T. Armstrong, E. K. Baines, E. K. Baines, K. Newman, K. Newman, M. Landavazo, M. Landavazo, B. Sun, B. Sun, S. R. Restaino, S. R. Restaino, } "Progress toward unprecedented imaging of stellar surfaces with the Navy precision optical interferometer", Proc. SPIE 9146, Optical and Infrared Interferometry IV, 91460A (24 July 2014); doi: 10.1117/12.2055789; https://doi.org/10.1117/12.2055789
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