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Photometric Characteristics of Data from the Hubble Space Telescope Goddard-High Resolution Spectrograph

Published online by Cambridge University Press:  19 July 2016

Dennis C. Ebbets ,
Sara R. Heap  and
Don J. Lindler
Dennis C. Ebbets
Affiliation:
Ball Aerospace Systems Division, P.O. Box 1062 JWF-3, Boulder, CO 80306 USA
Sara R. Heap
Affiliation:
NASA Goddard Space Flight Center, Greenbelt, MD 20771 USA
Don J. Lindler
Affiliation:
Advanced Computer Concepts, Potomac, MD 20854 USA

Abstract

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The G-HRS is one of four axial scientific instruments which will fly aboard the Hubble Space Telescope (ref 1,2). It will produce spectroscopic observations in the 1050 A ≤ λ ≤ 3300 A region with greater spectral, spatial and temporal resolution than has been possible with previous space-based instruments. Five first order diffraction gratings and one Echelle provide three modes of spectroscopic operation with resolving powers of R = λ/ΔΔ = 2000, 20000 and 90000. Two magnetically focused, pulse-counting digicon detectors, which differ only in the nature of their photocathodes, produce data whose photometric quality is usually determined by statistical noise in the signal (ref 3). Under ideal circumstances the signal to noise ratio increases as the square root of the exposure time. For some observations detector dark count, instrumental scattered light or granularity in the pixel to pixel sensitivity will cause additional noise. The signal to noise ratio of the net spectrum will then depend on several parameters, and will increase more slowly with exposure time. We have analyzed data from the ground based calibration programs, and have developed a theoretical model of the HRS performance (ref 4). Our results allow observing and data reduction strategies to be optimized when factors other than photon statistics influence the photometric quality of the data.

Type
I. Spectrographs, Detectors, Fourier Transform Spectroscopy, and Radial Velocities
Information
Symposium - International Astronomical Union , Volume 132: The Impact of Veryhigh S/N Spectroscopy on Stellar Physics , 1988 , pp. 35 - 38
Copyright
Copyright © Kluwer 1988 

References

1. Brandt, J.C. et al., “The High Resolution Spectrograph For The Space Telescope”, in The Space Telescope Observatory, Hall, D.N.B. ed., NASA CP2244, p. 76, 1982.Google Scholar
2. Ebbets, D.C., “High Resolution Spectrograph Instrument Handbook”, Space Telescope Science Institute, 1985.Google Scholar
3. Ebbets, D.C. and Garner, H.W., “Dead-time Effects in Pulse Counting Digicon Detectors”, Proceedings of SPIE, Vol. 627, Instrumentation in Astronomy VI, 1986, p 638.Google Scholar
4. Ebbets, D.C., “The Effects of Scattered Light and Detector Response Non-Uniformities on Signal to Noise Characteristics of HRS Data”, Proceedings of the Eighth Workshop on the Vacuum Ultraviolet Radiometric Calibration of Space Experiments, Boulder, 1987.Google Scholar