NIRSpec Performance Reports

The NIRSpec Performace Reports (NPR) included on this page cover issues related to the JWST/NIRSpec performances. More technical topics are addressed in NIRSpec Technical Notes available here. Documents listed in this page do not contain ITAR restricted or proprietary information.


TITLE: High-Resolution Modelling of the Spectral MSA Leakage
AUTHORS: A. Deshpande
TITLE: Assessing the Impact of the MSA Leakage on IFU Observations
AUTHORS: A. Deshpande
TITLE: The spectral calibration of JWST/NIRSpec: accuracy of the in- strument model for the OTIS test cycle
AUTHORS: Giovanna Giardino, Nora Luetzgendorf
TITLE: Mimicking the observation of an exoplanet transit:  analysis of a 3-hour exposure acquired at ISIM-CV3 and assessment of systematic effects
AUTHORS: Giovanna Giardino, Stephan Birkmann, Pierre Ferruit
TITLE: The spectral calibration of JWST/NIRSpec: accuracy of the instrument model for the ISIM-CV3 test cycle
AUTHORS: Giovanna Giardino, Nora Luetzgendorf
NPR-2015-002 TITLE: The accuracy of NIRSpec wavelength calibration – part 2: using the CAA sources as wavelength reference
AUTHORS: Giovanna Giardino, Pierre Ferruit
ABSTRACT: In this document we report the results of NIRSpec wavelength calibration performed using only the instruments internal sources: REF and LINES. We demonstrate that using these sources as reference the wavelength calibration for the six gratings can be achieved at a level of accuracy similar to that obtained with the external Argon source, using the simplified model optimization approach outlined in NPR-2014-004. Additionally we use the LINES sources to perform the wavelength calibration for the prism.
NPR-2014-005 TITLE: Flat-field reference files for observations through NIRSpec's fixed slits
AUTHORS: Guido De Marchi, Giovanna Giardino
ABSTRACT: This report describes the approach to remove from observations through NIRSpec's fixed slits the artefacts caused by variations in the pixel-to-pixel sensitivity of the detectors and by changes in the instrument response in the optical path (i.e. the flat-field correction). We present the flat-field reference files to be used in the data reduction pipeline for this purpose and describe how they were obtained from data collected during the second NIRSpec ground calibration campaign in 2013.
NPR-2014-004 TITLE: The accuracy of NIRSpec wavelength calibration: different strategies for the optimization of the instrument parametric model
AUTHORS: Giovanna Giardino, Pierre Ferruit

In this document we report on the accuracy of the wavelength calibration for NIRSpec that has been achieved using the method of optimizing the instrument parametric model for the second cycle (Cycle 2B) of NIRSpec Performance and Calibration Campaign, undertaken at IABG (Germany), in mid 2013. Using the external Argon lamp data, and applying the same optimization strategy that was used for the fit of the parametric model for Cycle 2A, results in a typical wavelength accuracy of better than 1/20 of a resolution element, for all gratings. This level of accuracy is very similar to that achieved for Cycle 2A, even though the number of spectral reference points available for Cycle 2B was less than a fourth of those for Cycle 2A. We explored also a simplified optimization approach, that only tries to optimize the alignment angles of the mirror and the dispersers at the Grating Wheel, reducing the number of
model free parameters by a factor of 10. We found that a similar level of accuracy in imaging positions and wavelength calibration can be achieved with this approach, as long as the position of quadrant 1 of the Micro Shutter Array is adjusted by a few micron, with respect to its Cycle 2A position. Finally, in view of developing a calibration strategy for when the instrument will be in space, a comparison between the accuracy of the models obtained using data from the NIRSpec internal calibration lamp CAA/REF and from the Argon source is also presented.

NPR-2014-003 TITLE: The wavelength stability of the CAA sourcs across two test
cycles of NIRSpec FM2
AUTHORS: G. Giardino
ABSTRACT: The NIRSpec calibration assembly (CAA) houses eleven sources to be used for the instrument calibraton and monitoring. In this document, we analyse the wavelength stability of the absorption lines of the REF source and of the emission features of the LINE1/2/3 sources of the CAA, across the two thermal cycles that NIRSpec underwent for Calibration and Performance Verification. To perform this analysis, an accurate parametric model of NIRSpec optical properties had to be derived for each of the two test cycles. We conclude that the lines of the REF source are stable in wavelength within 0.01 nm while those of the LINE sources are stable within 0.02-0.04 nm.
NPR-2013-011 TITLE: Optical Throughput of the NIRSpec Instrument
ABSTRACT: This report aims to demonstrate that the NIRSpec instrument meets all its requirements related to optical throughput. Using a series of exposures obtained during the first cryogenic calibration campaign in February 2011, and illuminated by different calibrated optical stimuli, we measure the end-to-end throughput of the NIRSpec optical train. Our results indicate that NIRSpec meets or exceeds all throughput requirements.
NPR-2013-009 TITLE: Status of the NIRSpec Focal Plane Array # 104 after the second (FM2) cyro campaign
AUTHORS: M. Sirianni
ABSTRACT: The Focal Plane Assembly 104 was installed in NIRSpec during the second flight module cryo campaign (FM2) at instrument level held between December 2012 and February 2013 at IABG in Germany. This report summarizes the performance of FPA104 during FM2 and compares it with those observed during the first cryo campaign (FM1) carried out between January and March 2011.
NPR-2013-008 TITLE: Calibration of the GWA position sensors - Part II
AUTHORS: C. Alves de Oliveira & G. De Marchi
ABSTRACT: This report presents a new method to calibrate the position sensors of the NIRSpec grating wheel assembly (GWA) based on spectral analysis. Several tests were devised and implemented to determine its accuracy and quantify the effects of the uncertainty in the mechanical angular reproducibility of the GWA on the wavelength calibration. The calibration of the sensors is achieved by applying this new method to over a thousand spectra extracted from the data acquired in the second calibration campaign of the flight model. It is shown that, using the sensors telemetry data, the position of a spectrum on the detector can be predicted with an accuracy greater than that required for wavelength calibration.
NPR-2013-007 TITLE: NIRSpec wavelength calibration accuracy
AUTHORS: S. Birkmann
ABSTRACT: This report summarizes the wavelength calibration of the NIRSpec instrument. Based on data acquired during on ground instrument level testing and our current understanding of the error budgets, NIRSpec will very likely meet its wavelength calibration accuracy requirements for all dispersers, although additional data is needed for the verification of the prism. The acquisition of this data will be part of the upcoming FM2 cycle 2 cryogenic testing.
NPR-2013-006 TITLE: Calibration of the GWA position sensors - Part III: Target acquisition accuracy
AUTHORS: G. De Marchi & G. Giardino
ABSTRACT: We have investigated the performance of the position sensors of the imaging mirror installed on the NIRSpec grating wheel assembly (GWA), using observations collected through the micro shutter array (MSA) during the second NIRSpec flight model ground calibration campaign. We confirm the previously reported tight relationship between the sensor's readings and the offset along the dispersion direction, across the entire field of view, with a residual scatter of less than 2.5 mas (RMS). As regards the cross-dispersion direction, we find that in most cases (85% of the trials) there is no systematic offset, with a repositioning accuracy better than 2.5 mas (RMS). The quoted accuracy also includes uncertainties on the geometrical transformations between the plane of the detector and that of the micro shutter array (MSA) and on their temporal stability, as well as on the uniformity of the MSA and detector metrology. These results are relevant for the NIRSpec target acquisition requirements, and we show that all components in the error budget pertaining to the NIRSpec opto-mechanical train and to its stability are met with ample margin.
NPR-2013-005 TITLE: Average Responsive Quantum Efficiency and average distribution of bad pixels in NIRSpec SCAs
AUTHORS: M. Sirianni
ABSTRACT: The current focal plane array installed in NIRSpec will be replaced later in the program. We do not yet have performed any test on the newly procured NIR detectors that will be used to build a new flight focal plane array. The calculation of the NIRSpec sensitivity for the instrument acceptance review requires as input the responsive quantum efficiency (RQE) of the detectors and also the average distribution of had pixels. In this document we derive an average RQE and an average bad pixels distribution based on the four detectors made available for NIRSpec as part of the first procurement.
NPR-2013-004 TITLE: Status and performance of the Micro Shutter System
AUTHORS: G. Giardino & G. De Marchi
ABSTRACT: In this report we summarize the results of the testing of NIRspec Micro Shutter System that was carried out during FM2 cycle 1 of NIRSpec Performance Verification and Calibration campaign. The report covers three main areas of MSA performances: the number and variability of failed open and failed closed shutters over the monitoring period and the MSA contrast properties. The impact of the number of failed shutters on NIRSpec Level 1 requirement is presented. The ‘glow' anomaly discovered in the early phase of the campaign is also discussed.
NPR-2013-003 TITLE: Duration of the NIRSpec Commissioning Activities
ABSTRACT: Motivated by the need to demonstrate that NIRSpec meets its allocated time for in-orbit commissioning, this report summarizes the status of the NIRSpec in-orbit commissioning plans, with special emphasis on the duration of the various activities required to ready NIRSpec for general science use. We conclude that NIRSpec meets the relevant requirement with ample margin.
NPR-2013-002 TITLE: NIRSpec Operational Efficiency
ABSTRACT: This report summarizes the current understanding of NIRSpec operational overheads, and provides an estimate for the in-orbit operational efficiency. Assuming a realistic mission scenario (i.e., a predicted distribution of visit lengths), the NIRSpec efficiency is shown to meet its requirement with margin. In addition, it is shown that the duration of the NIRSpec target acquisition procedure marginally violates the requirement.
NPR-2012-002 TITLE: Calibration of the GWA position sensors – Part I
AUTHORS: G. De Marchi
ABSTRACT: We have calibrated the position/tilt sensors of the NIRSpec grating wheel assembly (GWA) using the data collected during the first NIRSpec flight model ground calibration campaign. In this report we investigate the effects of the GWA repositioning uncertainty on the accuracy of the target acquisition process and of the wavelength calibration, showing that using the sensors' readings the required accuracy is met with ample margin.
NPR-2012-001 TITLE: Dependency of reference pixel Fourier-space weighting on temperature and environment
AUTHORS: G. Giardino
ABSTRACT: In this report we summarize the results of the analysis of the dependency of the reference pixel weighting on the operating temperature of the detector and the test environment. The method for deriving this Fourier-space weighting follows that described in JWST-RPT-015348 and is here briefly illustrated. Usage of the software package RefsubWeights that computes the weighting function is outlined in the Appendix. The Fourier-space weighting of the reference pixels provides only marginal improvements on the detector total noise figures for dark exposures, but does help in suppressing part of the striping present in the dark images due to the 1/f-noise component of the read noise. We find no signficant dependency of the weighting function on detector temperature changes of a few degrees.
NPR-2011-005 TITLE: NIRSpec best focus positions during cycle 1 FM testing
AUTHORS: S. Birkmann
ABSTRACT: This report describes the data, method, and results for estimating the best focus position of the NIRSpec instrument, obtained during the first ground calibration campaign in February 2011. Given the analysis presented here, it is likely that NIRSpec will meet its focus related performance requirements.
NPR-2011-003 TITLE: End-to-end Throughput of the NIRspec Instrument as derived from Cycle 1 data
ABSTRACT: This report describes the data, method, and results for estimates of the end-to-end throughput of the NIRSpec instrument, obtained during the first on-ground calibration campaign in February 2011. This preliminary analysis suggests that NIRSpec likely meets all performance requirements related to instrument throughput. Nevertheless, some areas of uncertainty remain which are related to the calibration of the OGSE used for the Cycle 1 measurements; these are discussed as well.
NPR-2011-002 TITLE: Temporal Stability of CAA Lamp Fluxes
AUTHORS: T. Böker and G. Giardino
ABSTRACT: We present a trending analysis to gauge the stability of the signal levels from the NIRSpec CAA lamps. For each combination of CAA lamp and dispersive element, we measure the count rates detected on a specific detector area throughout the duration of the first NIRSpec cryo-campaign in February 2011. The analysis demonstrates that over the test campaign, all lamps were stable to within less than one per cent of their average signal.
ESA-JWST-RP-11883 TITLE: Analysis of the NIRSpec Demonstration Model Measurements at Ambient
ABSTRACT: The scope of this document is to present our analyis of the optical measurements made on the NIRSpec Demonstration Model (DM) under ambient conditions in October 2008 at Astrium.