These fixed set of detector dark currents originate from a series of dedicated measurements made in revolution 650. Despite these significant advances, some problems still remain to be addressed. These include corrections for line asymmetry, velocity shifts and the grating profile removal. Each of these effects is briefly described below and, where possible, a quantitative estimate of the resulting uncertainty is given. The line profiles observed using AOT LWS04 are generally asymmetric, with the long wavelength wing being higher than the short wavelength one.
Transients are also present in grating spectra.
Various methods for removal of transient effects are being investigated. At present the cause for this discrepancy is not known and is under investigation. In OLP 8.7 the underlying grating profile is not removed. For LWS04, where the FP scans are quite short, the effect should be very small. For LWS03, however, there may be some effect on the slope of the continuum, depending on the extent of the FP scan at each grating position.