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Paper: The ASTRA Spectrophotometer: Design and Overview
Volume: 364, The Future of Photometric, Spectrophotometric, and Polarimetric Standardization
Page: 255
Authors: Adelman, S.J.; Gulliver, A.F.; Smalley, B.; Pazder, J.S.; Younger, P.F.; Boyd, L.J.; Epand, D.; Younger, T.
Abstract: The ASTRA Cassegrain Spectrophotometer and its automated 0.5-m f/16 telescope will soon be working together at the Fairborn Observatory near Nogales, Arizona. Scientific observations are expected to begin in 2007. We provide an overview of this project and review the design of the system. A separate paper in these Proceedings presents details of the data reduction and flux calibrations. The Nogales site averages 150 photometric nights per year. ASTRA should observe stars whose declinations are in the range +80° to −35°.

In an hour the system should obtain S/N = 200 observations of stars as faint as 9.5 mag after correction for instrumental errors. Vega will require about 25 seconds for observation and CCD readout. Usually the telescope will find its next target in less than a minute. A small CCD camera finds and centers the target and a second then guides on the zeroth order spectrum. The spectrophotometer uses both a grating and a cross-dispersing prism to produce spectra from both the first and the second orders simultaneously. The square 30 arc second sky fields for each order do not overlap. The resolution is 7 Å in second and 14 Å in first order. The wavelength range is approximately λλ3300–9000. We are initially using about 10 minutes/hour to observe Vega and secondary standard candidates.

Our scientific CCD is electronically cooled to −50° C with a water recirculation system heat sink. The same 4° C recycling water system provides thermal stabilization of the instrument. Our flat fielding system uses a second 0.5-m telescope to produce a collimated beam from a 100 μm pinhole illuminated by a quartz halogen lamp. When the two telescopes point at one another this “artificial star” is focused by the ASTRA telescope which is then rocked to expose the image from the top to the bottom of the entrance aperture.

A LINUX HP server at The Citadel will have databases of ASTRA observations. Each observing request has its own priority and observing window, ASTRA can observe standard stars at a regular rate throughout the night, any accessible target at a given time, and variable stars. ASTRA will produce considerable high quality data.

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