CASSIS: The Cornell Atlas of Spitzer/Infrared Spectrograph Sources. II.
  High-resolution observations
  The Infrared Spectrograph (IRS) on board the Spitzer Space Telescope observed
about 15,000 objects during the cryogenic mission lifetime. Observations
provided low-resolution (R~60-127) spectra over ~5-38um and high-resolution
(R~600) spectra over ~10-37um. The Cornell Atlas of Spitzer/IRS Sources
(CASSIS) was created to provide publishable quality spectra to the community.
Low-resolution spectra have been available in CASSIS since 2011, and we present
here the addition of the high-resolution spectra. The high-resolution
observations represent approximately one third of all staring observations
performed with the IRS instrument. While low-resolution observations are
adapted to faint objects and/or broad spectral features (e.g., dust continuum,
molecular bands), high-resolution observations allow more accurate measurements
of narrow features (e.g., ionic emission lines) as well as a better sampling of
the spectral profile of various features. Given the narrow aperture of the two
high-resolution modules, cosmic ray hits and spurious features usually plague
the spectra. Our pipeline is designed to minimize these effects through various
improvements. A super sampled point-spread function was created in order to
enable the optimal extraction in addition to the full aperture extraction. The
pipeline selects the best extraction method based on the spatial extent of the
object. For unresolved sources, the optimal extraction provides a significant
improvement in signal-to-noise ratio over a full aperture extraction. We have
developed several techniques for optimal extraction, including a differential
method that eliminates low-level rogue pixels (even when no dedicated
background observation was performed). The updated CASSIS repository now
includes all the spectra ever taken by the IRS, with the exception of mapping
observations.
