Performing a query

A query can be performed

  • by coordinates and a radius search
  • by target name
  • by Program ID
  • by AORkey
  • by a list of AORkeys or object names (by uploading an ascii file)

The result page will appear after a few seconds with one or several spectra. Each spectra either corresponds to a given AORkey (single target) or to a pointing (cluster observations).

Understanding the plots

Which background subtraction was used?

The spectrum that is displayed is the best spectrum determined by the CASSIS pipeline. It uses the best background removal method between by nod, by order, or no background subtraction. We refer to the main documentation for more details.

Choice of the wavelength grid

It is possible to change the axes style (linear, log), as well as the wavelength grid choice. The grid is either:

  • Wavesamp interpolation, meaning that the 2 nod spectra were interpolated on the common SSC wavesamp grid, which is also the grid for a tapered column extraction. The final spectrum shown is thus also on the wavesamp grid.
  • Full interleaved sampling, meaning that the 2 nod spectra are calculated for the observed wavelengths rather than an interpolation. The spectrum shown has twice more points than the wavesamp spectrum. It can be used to recover the maximum spectra sampling at the expense of signal-to-noise.
  • Full interleaved sampling -> Wavesamp interpolation, same as above, i.e., the nod spectra are calculated for the observed wavelengths, but the interleaved spectrum is interpolated on the wavesamp table. The interpolation is performed on twice more points than the "Nods->Wavesamp" version of the spectrum.

Again, we refer to the main documentation for details on the wavelength grid. The x-axis of the plots indicates the wavelength grid choice.

Colors, lines, and axes

The title of the plot indicates the version of CASSIS used, the AORkey, the name of the object (given by the observer, and the SIMBAD and NED resolved name if found), and the redshift (if it could be associated unambiguously). The mention "multiple" is indicated if several NED or SIMBAD hits were found at the location of the extracted spectrum and considering the Spitzer/IRS spatial resolution.

The spectrum is shown in different colors for the orders, blue for order 1, green for order 2, and orange for order 3 (only in diagnostics plots).

The error bars are shown in gray. Dark gray bars correspond to systematic errors while light gray bars correspond to the RMS errors.

Vertical lines show the location of the main spectral lines. The top axis gives the rest-frame wavelength if a redshift could be associated.

Advanced use

The bottom bar below each spectrum shows several options:

  • Download PS
  • Download SMART fits
  • Optimal extraction diagnostics
  • VO view

The use of Optimal extraction diagnostics is heavily encouraged as it shows the spectrum in various ways (background subtraction methods, wavelength grids, tapered column versus optimal extraction, etc...)

The "More detail" button gives a precice list of all the FOV IDs (corresponding to one nod position, one order, one module). It provides more information on the calibration, program ID etc... It gives the best background subtraction method per FOV ID as well as the source extent, in units of the point spread function FWHM. If a source is significantly extended, optimal extraction does not provide a reliable flux calibration, and the spectrum may not reflect the spectrum of the entire object. It is advised to check and download the tapered column extraction for these.

List of Acronyms

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