Hubble Space Telescope Primer for Cycle 11

4.5 Space Telescope Imaging Spectrograph (STIS)

---

STIS uses two-dimensional detectors operating from the ultraviolet to the near infrared (1150-11,000 Å) in support of a broad range of spectroscopic capabilities. STIS can be used to obtain spatially resolved, long-slit (or slitless) spectroscopy of the 1150-10,300 Å range at low to medium spectral resolutions (R ~ 500 to 17,000) with first-order gratings. Echelle spectroscopy at medium and high (R ~ 30,000 and 110,000) resolutions covering broad spectral ranges of ~ 800 or 200 Å, respectively, is available in the ultraviolet (1150-3100 Å). STIS can also be used for deep optical and solar-blind ultraviolet imaging.

The three 1024 x 1024 pixel detectors supporting spectroscopy and imaging applications are as follows.

• A solar-blind CsI (FUV) Multi-Anode Microchannel Array (MAMA) with a plate scale of 0.024"/pixel and a 25" x 25" FOV is available from 1150 to 1700 Å.
• A Cs₂Te (NUV) MAMA with a plate scale of 0.024"/pixel and a 25" x 25" FOV is available from 1600 to 3100 Å.
• A CCD with a plate scale of 0.05"/pixel and a 52" x 52" FOV is available from ~2000 to 11,000 Å.

The MAMA detectors support time resolutions down to 125 micro-sec in TIME-TAG mode, and the CCD can be cycled in ~20 sec with use of small subarrays. The CCD and the MAMAs also provide coronographic spectroscopy in the visible and ultraviolet. Coronographic CCD imaging is also supported.

4.5.1 Charge Transfer Efficiency (CTE) Performance

The STIS CCD is undergoing a gradual deterioration in performance due to exposure to the space radiation environment. This has lead to gradually decreasing CTE-which is worst for observations of faint targets-and an increasing number of hot pixels. Both of these effects primarily degrade CCD spectroscopy. At present, the degradation is significant, and will continue to get worse. Optical spectroscopy at high spatial resolution on HST has a finite lifetime-shorter than the planned life of the observatory. Therefore, we urge observers who require this scientific capability for their research to propose for it now and not wait until future cycles.

4.5.2 Increased MAMA Dark Rates following SM3B

Following the installation of the ACS during SM3B, temperatures in the aft shroud are expected to rise significantly. This will cause the backgrounds in the STIS MAMA detectors to be significantly higher. Users should expect dark count rates in both the FUV and NUV MAMAs to be comparable to the highest values currently seen: 30 global cts/s in the FUV MAMA (primarily concentrated in the "glow" region in the upper left quadrant), and 2000 global cts/s in the NUV MAMA.