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).
The following setup parameters are available for the Aperture Spectral Extraction strategy:
- 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 radius: This corresponds to the half-width of the extraction aperture in the cross-dispersion direction, although it is referred to as a "radius." The terminology will be updated at a future date. 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 background region is specified by using the Inner radius and Outer radius parameters for the sky annulus. These parameters correspond to the inner and outer bounds of the sky region in cross-dispersion direction and do not use circular apertures in spite of the terminology that is used. If the option to use the noiselesssky background is selected, the countrate 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.