How accurate is the level of the flux in the grism spectra?
The extraction aperture for grism extractions is 10 arcsec (full width). In GR2 (2006) and later data releases, the PSF is modeled and a correction is applied so that the level of the spectra is accurate for unresolved sources (within the limits of the photon, calibration, and model errors). No adjustment is made for resolved (non-gaussian PSF) sources, and there will be a significant reduction in the level of the spectra for large sources (greater than about 6 arcseconds). In addition, the spectral calibration error is estimated to be on the order of 5 to 10% in the middle of the grism orders, somewhat larger near the edge of each order.
