In-orbit commissioning of the near-infrared spectrograph on the James Webb Space Telescope

Space Telescopes and Instrumentation 2022: Optical, Infrared, and Millimeter Wave

Oliveira

et al. 2022

Self Cite

The NIRSpec instrument for the James Webb Space Telescope (JWST) is a highly versatile near-infrared spectrograph that can be operated in various observing modes, slit apertures, and spectral resolutions. Obtaining dedicated calibration data for all possible combinations of aperture and disperser is an intractable task. We have therefore developed a procedure to derive a highly realistic model of the instrument's optical geometry across the entire field of view, using calibration data acquired through only a subset of NIRSpec apertures, which nevertheless allows the light paths within the spectrograph to be accurately computed for all apertures and all observing modes. This parametric instrument model thus provides the basis for the extraction of wavelengthcalibrated spectra from any NIRSpec exposure, regardless of observing mode or aperture used. Optimizing the NIRSpec instrument model and deriving its final wavelength and astrometric calibration was one of the most crucial elements of the NIRSpec commissioning phase. Here, we describe the process of re-fitting the NIRSpec instrument model with in-orbit commissioning data, and present its final performance in terms of wavelength accuracy and astrometric calibration.

Section: Datamentioning

confidence: 99%

Astrometric and wavelength calibration of the NIRSpec instrument during commissioning using a model-based approach

Lützgendorf¹,

Space Telescopes and Instrumentation 2022: Optical, Infrared, and Millimeter Wave

Oliveira

et al. 2022

Self Cite

“…The first in-flight sweep of the MagArm across the shutters occurred on 27 February 2022, once the full optical bench reach safe operating temperature for various mechanism (< 42 K). 5 In total, 798 reconfigurations were performed over 121 days in Commissioning, 6.6 per day on average. However, the actual cadence was not uniform, with the most intense period occurring between mid-April and Standard MSA configurations were used extensively throughout Commissioning, including the self-descriptive ALLOPEN and ALLCLOSED and the pair of full checkerboards (CHKBD1x1-n, n=1,2), used primarily for shutter operability assessment.…”

Section: Msa Reconfigurationsmentioning

confidence: 99%

“…4 All T.D.R. : E-mail: tim.rawle@esa.int of the NIRSpec modes were approved for science operations by the end of the six-month JWST Commissioning phase, 5,6 with the MOS mode declared ready on 1 July 2022.…”

Section: Introductionmentioning

confidence: 99%

In-flight performance of the NIRSpec micro shutter array

Rawle¹,

Space Telescopes and Instrumentation 2022: Optical, Infrared, and Millimeter Wave

Franz

et al. 2022

Self Cite

The NIRSpec instrument on the James Webb Space Telescope (JWST) brings the first multi-object spectrograph (MOS) into space, enabled by a programmable Micro Shutter Array (MSA) of ∼250,000 individual apertures. During the 6-month Commissioning period, the MSA performed admirably, completing ∼800 reconfigurations with an average success rate of ∼96% for commanding shutters open in science-like patterns. We show that 82.5% of the unvignetted shutter population is usable for science, with electrical short masking now the primary cause of inoperable apertures. In response, we propose a plan to recheck existing shorts during nominal operations, which is expected to reduce the number of affected shutters. We also present a full assessment of the Failed Open and Failed Closed shutter populations, which both show a marginal increase in line with predictions from ground testing. We suggest an amendment to the Failed Closed shutter flagging scheme to improve flexibility for MSA configuration planning. Overall, the NIRSpec MSA performed very well during Commissioning, and the MOS mode was declared ready for science operations on schedule.

In-orbit Performance of the Near-infrared Spectrograph NIRSpec on the James Webb Space Telescope

Beck

Birkmann²,

et al. 2023

PASP

The Near-Infrared Spectrograph (NIRSpec) is one of the four focal plane instruments on the James Webb Space Telescope. In this paper, we summarize the in-orbit performance of NIRSpec, as derived from data collected during its commissioning campaign and the first few months of nominal science operations. More specifically, we discuss the performance of some critical hardware components such as the two NIRSpec Hawaii-2RG detectors, wheel mechanisms, and the microshutter array. We also summarize the accuracy of the two target acquisition procedures used to accurately place science targets into the slit apertures, discuss the current status of the spectrophotometric and wavelength calibration of NIRSpec spectra, and provide the “as measured” sensitivity in all NIRSpec science modes. Finally, we point out a few important considerations for the preparation of NIRSpec science programs.