Appendix B:
Legacy Instruments
In this appendix...
Several instruments have been removed from HST after years of successful operation (see Section 2.1). The observations from these instruments in the HST Data Archive form a rich source of information for Archival Research. We therefore provide here a brief description of these instruments. Further details may be found in the most recent HST Instruments Handbooks for these instruments or in the HST Data Handbook (see Section 1.2).
B.1 Space Telescope Imaging Spectrograph (STIS)
STIS was an extremely versatile instrument. It used two-dimensional detectors operating from the far-ultraviolet to the near-infrared (1150–11,000Å) in support of a broad range of spectroscopic capabilities. STIS was used to obtain spatially resolved, long-slit (or slitless) spectroscopy of the 1150–10,300Å range at low to medium spectral resolutions (R ~ 500 to 17,000) with first-order gratings. Echelle spectroscopy at medium and high resolutions (R ~ 30,000 and 110,000) covering broad spectral ranges of Dl ~ 800Å and 200Å, respectively, was available in the ultraviolet (1150–3100Å). STIS was also used for deep optical and solar-blind ultraviolet imaging.
The three 1024 x 1024 pixel detectors supporting spectroscopy and imaging applications were the following:
- A solar-blind CsI (FUV) Multi-Anode Microchannel Array (MAMA) with a plate scale of 0.024"/pixel and a 25" x 25" FOV which operated from 1150Å to 1700Å.
- A Cs2Te (NUV) MAMA with a plate scale of 0.024"/pixel and a 25" x 25" FOV operated from 1600Å to 3100Å.
- A CCD with a plate scale of 0.05"/pixel and a 52" x 52" FOV operated from ~ 2000Å to 11,000Å.
The MAMA detectors could be used in ACCUM or TIME-TAG modes, with the latter supporting time resolutions down to 125 micro-sec, and the CCD was able to cycle in ~ 20 sec when using small subarrays. The CCD and the MAMAs also provided coronagraphic spectroscopy in the visible and ultraviolet. Coronagraphic CCD imaging was also supported.
The STIS received between ~30% and 70% of the total observing time per HST Cycle during Cycles 7 through 12. The huge and diverse archive of STIS observations constitutes a unique source of high-resolution spectroscopic data in the ultraviolet and spatially-resolved spectroscopic data at ultraviolet and optical wavelengths.
A major closeout effort to improve the quality, accessibility, and homogeneity of STIS data is currently underway at STScI. Details on the closeout efforts are available at:
B.2 Faint Object Camera (FOC)
The FOC was designed to provide high-resolution images of small fields. It consisted of two independent optical relays that magnified the input beam by a factor of four (f/96) and two (f/48). A variety of filters, prisms (for slitless spectroscopy), and polarizers could be placed in the optical beam. The f/48 relay also had a longslit spectrograph. The FOC photocathodes limited the wavelength range from 1200 to 6000Å.
When corrected by COSTAR, the field of view (FOV) and pixel size of the f/96 camera were 7" x 7" (512 x 512 format) and 0.014" x 0.014", respectively; a field of 14" x 14" could be used with the 512 x 1024 pixel format and a rectangular pixel size of 0.028" x 0.014". Without COSTAR in the beam, the corresponding parameters for the f/96 camera were: 11" x 11" FOV in the 512 x 512 format with pixel size 0.0223" x 0.0223", and full-format field of 22" x 22" with 0.0446" x 0.0223" pixels. The corresponding values for the (little used) f/48 camera were twice those of the f/96 camera.
The f/96 camera was the primary FOC imaging workhorse. High voltage instabilities limited the use of the f/48 relay to mainly long-slit spectroscopy after the installation of COSTAR.
Most of the FOC data in the archive are unique because the spatial resolution of the FOC is greater than that of any current (or planned) HST instrument. Also, the UV sensitivity was significantly higher than WFPC2, but less than STIS, although a larger variety of filters was available. Finally, the polarizers in the f/96 relay had very low instrumental polarization and excellent polarizing efficiencies.
A major reprocessing of the entire FOC science archive has been completed by ST-ECF, CADC, and STScI. This effort substantially improves the data quality and homogeneity. For more information about the reprocessed data, contact the Archive Hotseat archive@stsci.edu. A similar reprocessing of the non-science data is currently underway. The science data can be retrieved currently through the High Level Science Product pages at MAST http://archive.stsci.edu/hlsp/index.html.
B.3 Faint Object Spectrograph (FOS)
The FOS (now in the Smithsonian National Air and Space Museum in Washington, D.C.) performed low and moderate resolution spectroscopy (R ~ 250 and 1300) in the wavelength range 1150 to 8500Å. A variety of apertures of different sizes and shapes were available which could optimize throughput and spectral or spatial resolution. Ultraviolet linear and circular spectropolarimetric capability was also available.
The low resolution mode had two gratings and a prism, and the R = 1300 mode had six gratings to cover the entire spectral range. The photon-counting detectors consisted of two 512-element Digicons, one which operated from 1150 to 5500Å (FOS/BLUE), and the other from 1620 to 8500Å (FOS/RED).
Most FOS data were acquired in accumulation and rapid-readout modes; periodic and image modes were used infrequently. Time resolutions as short as 30 msec were feasible. The electron image was magnetically stepped through a programmed pattern during the observations which provided for oversampling, compensation for sensitivity variations along the Digicon array, sky measures and/or measurement of orthogonally polarized spectra. Normally, data were read out in intervals that were short compared to the exposure time.
The FOS received about 20–25% of the total HST observing time over Cycles 1–6, studying a large and diverse range of science topics. Due to the polarimetric and large dynamic range capabilities, a substantial fraction of these data is and will remain unique.
A major reprocessing of the entire FOS archive, which has substantially improved the data quality and homogeneity, has been completed at the Space Telescope-European Coordinating Facility. Contact the Archive Hotseat at archive@stsci.edu if you are interested in obtaining the reprocessed data.
B.4 Goddard High Resolution Spectrograph (GHRS)
The GHRS had two, 500-element Digicon detectors, which provided sensitivity from 1100 to 1900Å (Side 1—solar blind) and 1150 to 3200Å (Side 2); these detectors offered photon-noise limited data if an observing strategy was undertaken to map out photocathode response irregularities with the FP-SPLIT option. Signal-to-noise ratios of 100 or more were routinely achieved, and upwards of 1000 on occasion.
The GHRS modes included a first order grating covering 1100–1900Å at R ~ 2,500 (285Å bandpass), four first order holographic gratings with very low scattered light covering 1150–3200Å at R ~ 25,000 (27–45Å bandpass), and cross-dispersed echelles at R ~ 80,000 over 1150–3200Å (6–15Å bandpass).
The GHRS had two apertures: the 2.0" Large Science Aperture (LSA), and 0.25" Small Science Aperture (SSA); post-COSTAR the aperture projections were reduced to 1.74" and 0.22", respectively. The SSA projected to one resolution element; thus, even pre-COSTAR data taken with this aperture had the designed spectral resolution, albeit at reduced throughput.
Some data were acquired at time resolutions as short as 50 milli-seconds in a Rapid Readout mode. Most observations were acquired in accumulation mode, which provided for oversampling, compensation for sensitivity variations along the Digicon array, and simultaneous monitoring of detector backgrounds. Routine observations of the onboard Pt-Ne emission line lamp provided data with well calibrated wavelengths.
The GHRS received about 20–25% of the total HST observing time over Cycles 1 through 6, resulting in a large and diverse range of high quality science data. Due to the high signal-to-noise ratio and large dynamic range capabilities in the far ultraviolet, much of this data is unique.
A major reprocessing of the entire GHRS science archive has been completed by ST-ECF, CADC, and STScI. This effort substantially improves the data quality and homogeneity. A similar reprocessing of the non-science data is currently underway. Contact the Archive Hotseat at archive@stsci.edu if you are interested in obtaining the reprocessed data. The science data can be retrieved currently through the High Level Science Products page at MAST.
B.5 High Speed Photometer (HSP)
The HSP was designed to take advantage of the lack of atmospheric scintillation for a telescope in orbit, as well as to provide good ultraviolet performance. Integrations as short as 10 ms were possible over a broad wavelength range (1200 to 8000Å), and polarimetry was also possible. Observations were carried out through aperture diameters of 1.0" with the visual and ultraviolet detectors, and 0.65" with the polarimetry detector.
HSP had a large variety of fixed aperture/filter combinations distributed in the focal plane; selection was accomplished by moving the telescope so as to place the target in the desired aperture behind the desired filter.
The HSP detectors consisted of four image-dissector tubes and one photomultiplier tube. A variety of ultraviolet and visual filters and polarizers was available. This instrument was used for only a relatively small fraction (5%) of HST observing in Cycles 1 to 3, since the HSP science program was among the more severely compromised by spherical aberration. Only limited instrument expertise is available at STScI in support of HSP Archival Research. The extremely high speed with which some HSP data was acquired remains unmatched by past, current, or planned HST capabilities.
B.6 Wide Field and Planetary Camera 1 (WF/PC)
The WF/PC had two configurations; in both, the FOV was covered by a mosaic of four charge-coupled devices (CCDs). Each CCD had 800 ¥ 800 pixels and was sensitive from 1150 to 11,000Å. However, internal contaminants on the camera optics limited normal operation to the range from 2840 to 11,000Å.
In the Wide Field Camera (low-resolution) configuration, the FOV was 2.6' x 2.6', with a pixel size of 0.10". In the Planetary Camera (high-resolution) configuration, the FOV was 1.1' x 1.1' and the pixel size was 0.043". A variety of filters was available. The WF/PC received about 40% of the observing time on HST in Cycles 1 to 3, resulting in a large and diverse range of science data. All WF/PC data were severely affected by the spherical aberration. Unique and valuable data exist in the archive, but in terms of photometric accuracy, and especially image quality, data taken after the first servicing mission with (e.g., with the WFPC2) are superior.
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