The Near-Infrared Spectrograph (NIRSpec) on the James Webb Space Telescope

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

Bhatawdekar²,

Birkmann³

et al. 2022

To achieve its ambitious scientific goals, the Near-Infrared Spectrograph, NIRSpec, on board the Webb Space Telescope, needs to meet very demanding throughput requirements, here quantified in terms of photon-conversion efficiency (PCE). During the calibration activities performed for the instrument commissioning, we have obtained the first in-flight measurements of its PCE and also updated the modeling of the light losses occurring in the NIRSpec slit devices.The measured PCE of NIRSpec fixed-slit and multi-object spectroscopy modes overall meets or exceeds the pre-launch model predictions. The results are more contrasted for the integral-field spectroscopy mode, where the differences with the model can reach −20%, above 4 µm, and exceed +30%, below 2 µm. Additionally, thanks to the high quality of the JWST point-spread function, our slit-losses, at the shorter wavelength, are significantly decreased with respect to the pre-flight modeling.These results, combined with the confirmed low noise performance of the detectors, make of NIRSpec an exceptionally sensitive spectrograph.

mentioning

confidence: 65%

“…PCE performance was predicted to be approximately 50% to 10% lower, going from the blue-to the red-end of NIRSpec operating wavelength range [8], since the IFS introduces eight further reflections.…”

mentioning

confidence: 99%

Optical throughput and sensitivity of JWST NIRSpec

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

Bhatawdekar²,

Birkmann³

et al. 2022

“…Operating in the near infrared in the wavelength range of 0.6 − 5.3 µm, and using a collection of gratings and a prism that allow to take spectra in low (R=100), medium (R=1000) and high (R=2700) resolution, NIRSpec is designed to take up to 200 spectra at once, for example to study high-redshift galaxies and the early universe. A detailed description of the NIRSpec design, observing modes, and scientific use cases can be found in [1][2][3][4].…”

Section: Introductionmentioning

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

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.

“…This versatile instrument 1 provides multiple complementary capabilities to explore a wide range of science themes. Users are given a choice in wavelength range and spectral resolution (R∼100 over the full range, or R∼1000, 2700 in one of three wavelength bands) as well as several aperture options: precision fixed slits for high-contrast high-throughput single-object spectroscopy, such as in time-series observations, 2 a 3×3 arcsec integral field unit (IFU) for spatially-resolved spectroscopy, 3 and, as a first for an observatory in space, the Micro Shutter Array (MSA) enabling multi-object spectroscopy (MOS). 4 All T.D.R.…”

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

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.