CALPRODUCT-NS-001: NISP-S 0th Order Centroid SED Dependence Calibration¶
Parent requirement¶
Scheduling¶
Once.
An immediate calibration during PV is not required; it can be built up over time as the wide survey grows and sources with very different SEDs are mapped at different positions in the focal plane.
Time-critical¶
No.
Objective¶
The 0th-order in the spectra images has a double-peaked, peanut-like shape - that also varies across the field of view - for two reasons:
The prism in the grism introduces some dispersive power even in 0th-order, resulting in a ~10 pixel long spectrogram;
The grating in the grism is blazed for a specific wavelength in the spectral domain, resulting in near zero transmission at this wavelength in all non-1st-order spectrograms (and conversely maximum transmission at this same wavelength in the 1st order).
In the calibration procedure, the reference 0th-order position is derived from the mean of the 2 single-peak positions. The main impact of the source SED is to change the ratio of the 2 peaks, and therefore the inferred mean value. To a lesser degree, it also affects the single peak positions, likely at the sub-pixel level, only. These impacts must be quantified, calibrating the SED dependence of the 0th order centroid position.
Fulfilled by¶
Data volume¶
No dedicated observations needed.
Processing input¶
Ground Processing Input Data: All calibration products to run the standard science pipeline (BPM, darks, flat, nonlinearity etc), astrometric reference catalog (Gaia).
Data Description: No dedicated observations needed!
Processing method¶
The necessary color information can be extracted from the NISP-P photometry directly, or directly from the grism spectra.
Processing output¶
Relationship between infrared SED and 0th order centroid metrics.
The calibration product can be built up over time as the wide survey grows and sources with very different SEDs are mapped at different positions in the focal plane.
Required accuracy, constraints¶
accurate 0th order centroid measurements, color information retrieved for 0th order sources
Processing tools¶
L1 science pipeline, source position measurements, color/SED information for sources with good SNR 0th order spectra. Since it is not well known what to expect in terms of SED dependence, this analysis requires considerable human intervention, to quantify the effect and to decide to what extent a calibration and / or correction is needed.
Quality control parameters¶
DataModel: https://gitlab.euclid-sgs.uk/
Contact person¶
NISP-S instrument scientist.