AAS 198th Meeting, June 2001
Session 61. Optical Interferometry I - CHARA
Display, Wednesday, June 6, 2001, 10:00am-7:00pm, Exhibit Hall

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[61.03] The Two-Beam IR Beam Combiner at the CHARA Array

J. Sturmann, T. A. ten Brummelaar (Georgia State University CHARA), S. T. Ridgway (NOAO and Georgia State University CHARA), H. A. McAlister, M. A. Shure, L. Sturmann, N. H. Turner (Georgia State University CHARA)

The two-beam combination and IR detection system serves as a test and commissioning instrument during the integration phase of the CHARA Array. This two-beam IR system is capable of providing new and interesting astronomical data by combining the light from any two of the six telescopes in the array.

Fringes are produced using a classical Michelson interferometer, and are imaged to single element InSb nitrogen cooled detectors. After a dichroic split, data are collected simultaneously in H and K bands around 1.6 and 2.2 microns. There are four detectors, two for each wavelength band. The low-pass filtered detector signals are digitized and recorded individually.

During data collection, a real time display of the raw or band-pass filtered data is available. We are also able to see the fringes in real time by displaying sums and differences of the channels. In one arm of the interferometer, a mirror is mounted on a piezoelectric translation stage, which is driven by a saw tooth periodic voltage typically of 1 Hz. With this dithering mirror, we are able to sweep back and forth through the fringes, which allows a high rate of data acquisition for good statistics, and provides a simple means of fringe tracking.

The CHARA Array, a six-telescope O/IR interferometric array operated by Georgia State University was funded by the National Science Foundation, the W. M. Keck Foundation, the David and Lucile Packard Foundation, and the Georgia State University.

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