The JWST ETC Aperture Spectral Extraction strategy is used for spectroscopic modes, including slit spectroscopy with NIRSpec and MIRI, and slitless spectroscopy modes (NIRISS wide field slitless spectroscopy, NIRCam wide field slitless spectroscopy, and MIRI low-resolution spectroscopy).
- Aperture location:
- The aperture may be centered on any desired source within the scene used for the slitless spectroscopy calculation. The drop-down menu is populated with a list of the sources available in the scene from which the selection can be made. For fixed slit spectroscopy, if there are multiple sources located within the slit along the cross-dispersion direction, they may be selected from the drop-down menu.
- The aperture can be chosen to be at any desired location within the slit along the cross-dispersion direction by specifying the Y-offset in arcsec from the slit center.
- Aperture Half-Height: This corresponds to the half-height of the extraction aperture in the cross-dispersion direction. The spectral extraction is performed over the full extent of the specified extraction aperture.
- Perform Background Subtraction Using: As in the case of imaging, there is an option to perform background subtraction using the background estimated from a background region specified by the user, or using a noiseless sky background. The latter may be preferred when the scene has other sources that may contribute a non-uniform background to the aperture. The effect of non-uniform backgrounds may be estimated by performing two calculations; with and without the background contamination from within the other sources in the scene.
The Sky sample region is specified by using the Start region and End region parameters. These parameters correspond to the inner and outer bounds of the sky region in cross-dispersion direction. If the option to use the noiseless sky background is selected, the count rate corresponding to the sky background chosen under the Backgrounds tab is used for background subtraction. Note that when a background region is specified, it also includes contamination from other overlapping regions when multiple sources are present, extended emission if present, or extended profiles that contribute to the background extraction aperture. When the background subtraction is performed, the contamination and sky contribution are subtracted. When the noiseless sky background is opted for background subtraction, the contamination is not subtracted from the extracted source flux.
- Wavelength of Interest: This specifies the wavelength at which the scalar quantities are reported in the reports.