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The Goddard High Resolution Spectrograph: In-Orbit Performance



S R. Heap, J L. Linsky


The in-orbit performance of the Goddard High Resolution Spectrograph onboard the Hubble Space Telescope (HST) is presented. This report covers the pre-COSTAR period, when instrument performance was limited by the effects of spherical aberration of the telescope's primary mirror. The digicon detectors provide a linear responce to count rates spanning over six orders of magnitude, ranging from the normal background flux of 0.01 counts diode-1s-1 to values larger than 104 counts diode-1s-1. Scattered light in the echelle mode is more complex in origin, but it also can be accurately removed. Data has been obtained over a wavelength range from below 1100 A to 3300 A, at spectral resolutions as high as (R=λ/Δ}λ=90,0000). The wavelength scale is influenced by specturograph temperature, outgassing of the optical bench, and interaction of the magnetic field within the detector with the earth's magnitude field. Models of these effects lead to a default wavelength scale with an accuracy better than 1 diode, corresponding to 3 km s-1 in the echelle mode. With care, the wavelength scale can be determined to an accuracy of 0.2 diodes. Calibration of the instument sensitivity functions is ties into the HST flux calibration through observations of spectrophotometric stand stars. The measurements of vignetting and the echelle blaze function provide relative photometric precision to about 5% or better. The effects of fixed-pattern noise have been investigated, and techniques have been devised for recognizing and removing ir from the data. The ultimate signal-to-noise ratio achievable with the spectrograph is essentially limited only by counting statistics, and values approaching 1000: 1 have been obtained.
Publications of the Astronomical Society of the Pacific


astronomical instruments, Hubble Space Telescope, ultraviolet spectroscopy


Heap, S. and Linsky, J. (2021), The Goddard High Resolution Spectrograph: In-Orbit Performance, Publications of the Astronomical Society of the Pacific (Accessed April 14, 2024)
Created October 12, 2021