3.1 Instrument Capabilities

STIS uses two-dimensional detectors operating from the ultraviolet (UV) to the near-infrared (NIR). First-order gratings cover the full spectral range and are designed for spatially resolved spectroscopy using a long slit. The echelle gratings, available only in the UV, are designed to maximize the spectral coverage in single observations of point sources. The STIS Flight Software supports onboard target acquisitions and peakups to place targets on slits. The STIS optics and detectors have been designed to exploit HST's high spatial resolution.

STIS can be used to obtain:

  • Echelle spectroscopy at medium to high spectral resolution (R ~ 30,000–114,0001), covering a broad simultaneous spectral range (Δλ ~ 800 or 200 Å, respectively) between 1150–3100 Å.
  • Spatially resolved, long-slit (or slitless) spectroscopy from the UV to the NIR (1150–10,300 Å) at low to medium spectral resolution (R ~ 500–17,000) in first order.

In addition to these two prime capabilities, STIS also provides:

  • Imaging capability using the solar-blind FUV-MAMA detector (1150–1700 Å), the solar-insensitive NUV-MAMA detector (1150–3100 Å), and the optical CCD (2000–10,300 Å), through a small complement of narrow-band and broad-band filters.
  • Slitless spectroscopy (R ~ 10-500) between 1150–3100 Å.
  • High time-resolution (Δτ = 125 microseconds) imaging and spectroscopy between 1150–3100 Å and moderate-time-resolution (Δτ ~ 20 seconds) CCD imaging and spectroscopy between 2000–10,300 Å.
  • Coronagraphic imaging between 2000–10,300 Å and bar-occulted spectroscopy over the entire spectral range (1150–10,300 Å).
  • Spatially scanned spectra with the STIS CCD (2000–10,300 Å).

Table 4.1 and Table 5.1 provide a full list of gratings for spectroscopy and filters for imaging.

STIS is a versatile instrument that can be used for a broad range of scientific programs. The 50-arcsecond long slit and high quantum efficiency in the optical, provided by the CCD, enables spatially resolved spectroscopy of extended and/or diffuse astronomical sources. This is particularly important for studies of the dynamics of galactic nuclei, the kinematics of active galaxies, and the properties of diffuse galactic nebulae. The wide wavelength coverage of STIS facilitates line-ratio studies; for instance, the low-resolution first-order gratings span the range 1150–10,300 Å in just four exposures. Slitless spectroscopy provides emission-line images of astronomical objects, and coronagraphic imaging and spectroscopy can reveal the nature of extended gaseous regions surrounding bright continuum sources.  Spatial scanning can yield very high-S/N ratio spectra and very reproducible fluxes (in broad or narrow bands) for time series studies (e.g., of exoplanets and their atmospheres).

1 In the past, it was possible to achieve R ~ 200,000 with the 0.1 × 0.03 aperture; however, recently we have seen that the smallest apertures are negatively impacted by degrading focus. The maximum resolution achievable by these small apertures could be affected (see STIS ISR 2017-01 for more information about the degrading focus and Section 12.6 for more information about improving the sampling of the line-spread function).