JWST - Papers - JWST NIRSpec
Papers on NIRSpec's Performances
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| AUTHOR(S): | Anurag Deshpande, Nora Lützgendorf, Pierre Ferruit et al. |
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The Near Infrared Spectrograph (NIRSpec) instrument is one of the four scientific instruments aboard the James Webb Space Telescope (JWST). NIRSpec can be operated in Multi-Object Spectroscopy (MOS), Fixed- slit Spectroscopy (FS), and Integral Field Spectroscopy (IFS) modes; with spectral resolutions from 100 to 2700. Two of these modes, MOS and IFS, share the same detector real estate and are mutually exclusive. Consequently, the micro-shutters used to select targets in MOS mode must all be closed when observing in IFS mode. However, due to the finite contrast of the micro-shutter array (MSA), some amount of light passes through them even when they are commanded closed. This light creates a low, but potentially significant, parasitic signal, which can affect IFS observations. Here, we present the work carried out to study and model this signal. Firstly, we show the results of an analysis to quantify its levels for all NIRSpec spectral bands and resolution powers. We find a level of parasitic signal that is, in general, lower than 10% of the incident, extended IFS signal. We also show how these results were combined with signal-to-noise considerations to help consolidate the observation strategy for the IFS mode and to prepare guidelines for designing observations. In general, we find that this parasitic signal will be less than the statistical noise of a Zodiacal light exposure up to ∼40 groups for the NIRSpec grating configurations, and ∼10 groups for the prism configuration. In a second part, we report on the results of our work to model and subtract this signal. We describe the model itself, its derivation, and its accuracy as determined by applying it to ground test data. |
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| AUTHOR(S): | Catarina Alves de Oliveira, Stephan Birkmann, Torsten Böker, et al. |
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The Near-Infrared Spectrograph (NIRSpec) is one of four instruments aboard the James Webb Space Telescope (JWST). NIRSpec is developed by ESA with AIRBUS Defence & Space as prime contractor. The calibration of its various observing modes is a fundamental step to achieve the mission science goals and provide users with the best quality data from early on in the mission. Extensive testing of NIRSpec on the ground, aided by a detailed model of the instrument, allow us to derive initial corrections for the foreseeable calibrations. We present a snapshot of the current calibration scheme that will be revisited once JWST is in orbit. |
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| AUTHOR(S): | Catarina Alves de Oliveira, Stephan Birkmann, Torsten Böker, et al. |
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The Near-Infrared Spectrograph (NIRSpec) is one of four instruments aboard the James Webb Space Telescope (JWST). NIRSpec is developed by ESA with AIRBUS Defence & Space as prime contractor. The calibration of its various observing modes is a fundamental step to achieve the mission science goals and provide users with the best quality data from early on in the mission. Extensive testing of NIRSpec on the ground, aided by a detailed model of the instrument, allow us to derive initial corrections for the foreseeable calibrations. We present a snapshot of the current calibration scheme that will be revisited once JWST is in orbit. |
| TITLE: | Noise Performance of the JWST/NIRSpec Detector System (presented at SPIE 2018) |
| AUTHOR(S): | Stephan Birkmann, Marco Sirianni, Pierre Ferruit et al. |
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The Near-Infrared Spectrograph (NIRSpec) is one of the four science instruments onboard the James Webb Space Telescope (JWST). The instrument features a focal plane array (FPA) consisting of two 2048 x 2048 HAWAII-2RG sensor chip assemblies (SCAs) with a cutoff wavelength of approximately 5.3 μm. The detectors are read out via a pair of SIDECAR ASICs. To ensure a stable operating environment and best performance, the FPA is temperature controlled via a dedicated control loop by the NIRSpec focal plane electronics. The targeted in-orbit operating temperature of the NIRSpec FPA is close to 42.8 K. Due to the low background levels that the JWST will provide, most NIRSpec observations of very faint targets will be detector noise limited. Therefore, stringent noise requirements on the detector system were put in place. In order to meet these requirements, NIRSpec offers a dedicated readout mode for its detectors that is called improved reference sampling and subtraction (IRS2). In this paper we present the noise performance of the NIRSpec detectors as a function of readout mode and exposure parameters. We find that the NIRSpec detector system meets its stringent noise requirement of 6 electrons total noise in a ~1000 second exposure. We also highlight the types and effects of different kinds of bad pixels that are present in the detectors in small numbers. |
| TITLE: | Operability assessment concept for the JWST/NIRSpec micro-shutter array (MSA) (presented at SPIE 2018) |
| AUTHOR(S): | Timothy Rawle, Giovanna Giardino, Catarina Alves de Oliveira et al. |
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JWST/NIRSpec will include the first space-borne multi-object spectrograph, comprising a micro-shutter array (MSA) of a quarter of a million closable apertures that can be individually addressed to select up to a couple of hundred objects within a ~3.2x3.4 arcmin field of view. Although more than ~85% of the unvignetted shutters are fully operational, the high degree of mechanical movement combined with complex circuitry on a small scale, inevitably leads to some non-operable shutters. In this paper we present an overview of the operability assessment concept for the MSA, employed during both ground tests and in flight. We describe the procedures used to detect, mitigate against, and even repair the non-operable shutters, and show the effect upon the multiplexing capability and output data from NIRSpec. We also present the operability trending results from ground tests, and discuss the probable impact on nominal operations after launch. |
| TITLE: | Uncovering the Early Stages of Galaxy Evolution: Multi-Object Spectrometry with JWST/NIRSpec |
| AUTHOR(S): | Giovanna Giardino, Catarina Alves de Oliveira, Santiago Arribas et al. |
| ABSTRACT: |
The James Webb Space Telescope (JWST) will be one of the great observatories of the next decade. NIRSpec (Near Infrared Spectrograph) is the near-infrared multi-object spectrograph of the JWST and it features 730 x 342 individually addressable shutters of 0.2'' (width) x 0.5'' (cross-dispersion), covering a 9 arcmin-square field for Multi-object spectroscopy in the wavelength range 0.6-5.0 micron, at a spectral resolution of 100-1000. The instrument is already integrated in JWST payload module and has recently undergone a series of detailed calibration tests, in cryogenic environment, confirming its excellent capabilities. Here we provide an overview of the MOS mode of NIRSpec and its performance, and discuss how the combination of NIRSpec multi-plexing and high sensitivity will allow observations of thousands of galaxies throughout a wide redshift range (typically 2-8) to be obtained, shedding new light into the phyiscs of galaxy assembly and evolution.
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| TITLE: | The JWST/NIRSpec instrument: update on status and performances (presented at SPIE 2016) |
| AUTHOR(S): | Stephan M. Birkmann, Pierre Ferruit, Tim Rawle et al. |
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The Near-Infrared Spectrograph (NIRSpec) is one of the four instruments on the James Webb Space Telescope (JWST) which is scheduled for launch in 2018. NIRSpec was developed by the European Space Agency (ESA) with Airbus Defense & Space Germany as prime contractor. The instrument offers seven dispersers covering the wavelength range from 0.6 to 5.3 micron with resolutions from R ∼ 100 to R ∼ 2700. Using an array of micro-shutters NIRSpec will be capable of obtaining spectra for more than 100 objects simultaneously. It also features an integral field unit with 3” x 3” field of view and various slits for high contrast spectroscopy of individual objects and time series observations of e.g. transiting exoplanets. NIRSpec is now in its final flight configuration and underwent cryogenic performance testing at the Goddard Space Flight Center in Winter 2015/16 as part of the Integrated Science Instrument Module (ISIM). We present the current status of the instrument and also provide an update on NIRSpec performances, based on results from the latest test campaign. |
| TITLE: | The spectral calibration of JWST/NIRSpec: results from the recent cryo-vacuum campaign ISIM-CV3 (presented at SPIE 2016) |
| AUTHOR(S): | Giovanna Giardino, Nora Luetzgendorf, Pierre Ferruitet al. |
| ABSTRACT: |
The NIRSpec instrument of JWST can be operated in multi-object (MOS), long-slit, and integral field mode with spectral resolutions from 100 to 2700. Its MOS mode uses about a quarter of a million individually addressable mini-slits for object selection, covering a field of view of ∼ 9 square-arcminute. We have developed a procedure to optimize a parametric model of the instrument that provides the basis for the extraction of wavelength calibrated spectra from NIRSpec data, from any of the apertures and for all the modes. Here, we summarize the steps undertaken to optimize the instrument model parameters using the data acquired during the latest cryo-vacuum campaign of the JWST Integrated Science Instrument Module, recently carried out at NASA Goddard Space Flight Center. The calibrated parametric model is able to reproduce the spatial and spectral position of the input spectra with an intrinsic accuracy (1-sigma, RMS) ~ 1/10 of a pixel in spatial and spectral direction for all the modes. The overall wavelength calibration accuracy (RMS) of the model as measured on the extracted spectra is better than 1/20 of a resolution element for all of the grating-based spectral modes and at the level of 1/14 of a resolution element for the prism. These results are well within the allocations for the model in the overall spatial and spectral calibration budget of NIRSpec. |
| TITLE: | The JWST/NIRSpec Exoplanet Exposure Time Calculator (presented at SPIE 2016) |
| AUTHOR(S): | Louise Dyregaard Nielsen, Pierre Ferruit, Giovanna Giardino et al. |
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The James Webb Space Telescope (JWST), with its unprecedented sensitivity, will provide a unique set of tools for the study of transiting exoplanets and their atmospheres. The Near Infrared Spectrograph (NIRSpec) is one of four scientific instruments on JWST and offers a high-contrast aperture-spectroscopy mode developed specifically for exoplanet observations. Here we present the NIRSpec Exoplanet Exposure Time Calculator (NEETC) software, an exposure time calculator optimized to evaluate the signal-to-noise ratio and simulate spectra for observations of transiting exoplanets. The NEETC is being developed to help the NIRSpec instrument team, and ultimately future JWST users, to fully investigate NIRSpec’s observation modes and the feasibility of exoplanet observations. We give examples of how the NEETC can be used to prepare observations, and present results highlighting the capabilities and limitations of NIRSpec. |
| TITLE: | Flat-fielding Strategy for the JWST/NIRSpec Multi-Object Spectrograph (presented at SPIE 2016) |
| AUTHOR(S): | Tim D. Rawle, Catarina Alves de Oliviera, Stephan M. Birkmann et al. |
| ABSTRACT: | The Near-Infrared Spectrograph (NIRSpec) onboard the James Webb Space Telescope (JWST) will be the first space-borne Multi-Object Spectrograph (MOS), comprising a quarter of a million individually addressable microshutters to allow simultaneous observation of ∼100 targets. We present the strategy for flat-fielding the NIRSpec MOS, correcting for the combined effects of the telescope and instrument throughput as well as the detector response. With a highly configurable shutter array, a novel approach is required to ensure that flat- field reference observations do not significantly impact telescope efficiency. We envisage a two-step strategy: 1) Creation of a three-dimensional master flat-field reference (two spatial dimensions, one wavelength) from a small set of well-designed calibration data; 2) Correction of any data frame using a two-dimensional flat-field generated on-the-fly, for that specific MOS configuration, from the master. |
| TITLE: | A model-based approach to the spatial and wavelength calibration of NIRSpec on board JWST (A&A Accepted for publication) |
| AUTHOR(S): | Bernhard Dorner, Giovanna Giardino, Pierre Ferruit et al. |
| ABSTRACT: | Context. The NIRSpec instrument for the James Webb Space Telescope (JWST) can be operated in multi-object (MOS), long-slit, and integral field (IFU) mode with spectral resolutions from 100 to 2700. Its MOS mode uses about a quarter of a million individually addressable mini-slit for object selection, covering a field of view of approx. 9 square-arcmin. Aims. The pipeline that will be used to extract wavelength-calibrated spectra from NIRSpec detector images relies heavily on a model of NIRSpec optical geometry. We demonstrate how dedicated calibration data from a small subset of NIRSpec modes and apertures can be used to optimize this parametric model to the necessary levels of fidelity. Methods. Following an iterative procedure, the initial fiducial values of the model parameters are manually adjusted and then automatically optimized, so that the model predicted location of the images and spectral lines from the fixed slits, the IFU, and a small subset of the MOS apertures matches their measured location in the main optical planes of the instrument. Results. The NIRSpec parametric model is able to reproduce the spatial and spectral position of the input spectra with high fidelity. The intrinsic accuracy (1-sigma, RMS) of the model, as measured from the extracted calibration spectra, is better than 1/10 of a pixel along the spatial direction and better than 1/20 of a resolution element in the spectral direction, for all grating-based spectral modes. This is fully consistent with the corresponding allocation in NIRSpec's spatial and spectral calibration budgets. |
| TITLE: | Status of the JWST/NIRSpec instrument (presented at SPIE 2014) |
| AUTHOR(S): | Stephan M. Birkmann, Pierre Ferruit, Catarina Alves de Oliveira et al. |
| ABSTRACT: | The Near-Infrared Spectrograph (NIRSpec) is one of the four instruments on the James Webb Space Telescope (JWST), scheduled for launch in 2018. NIRSpec has been designed and built by the European Space Agency (ESA) with Airbus Defense and Space Germany as prime contractor. The instrument covers the wavelength range from 0.6 to 5.3 micron and will be able to obtain spectra of more than 100 astronomical objects simultaneously by means of a configurable array of micro-shutters. It also features an integral field unit and a suite of slits for high contrast spectroscopy of individual objects. The extensive ground calibration campaign of NIRSpec was completed in Summer 2013, after which it was delivered to NASA for integration into the Integrated Science Instrument Module (ISIM). We highlight the major results from the instrument level calibration campaign which demonstrated full compliance with all opto-mechanical performance requirements. In addition, we present the current status of the instrument, describe the ongoing preparations for the Integrated Science Instrument Module (ISIM) test campaign to begin in June 2014, and briefly discuss plans for the pending exchange of the detector and micro-shutter assemblies following the first ISIM test cycle. |
| TITLE: | Observing transiting exoplanets with JWST/NIRSpec (presented at SPIE 2014) |
| AUTHOR(S): | Pierre Ferruit, Stephan M. Birkmann, Torsten Böker et al. |
| ABSTRACT: | Recent publications resulting from observations conducted with the Hubble Space Telescope (HST) have highlighted the diagnostic power of near-infrared spectroscopy for the study of the atmospheric properties of transiting exoplanets. In this context, the James Webb Space Telescope (JWST) and it suite of instruments will have an unprecedented combination of sensitivity and spectral coverage. In this article, we focus on one of these instruments, the near-infrared spectrograph NIRSpec. NIRSpec will offer an aperture spectroscopy mode dedicated to the characterization of transiting exoplanets. It will cover the 0.6-5.3 μm spectral domain with 3 ranges of spectral resolution (R 100, 1000 and 2700). The predicted noise floor (photon noise and detector noise only, no systematics included) is lower than 100 ppm for a single 1-hour in-transit observation of an 7th magnitude star, indicating that transit spectroscopy programs with NIRSpec will routinely have photon-noise limited noise floors of a few tens of ppm. In terms of brightness limits, at high spectral resolution, NIRSpec will be able to observe planets transiting stars with J-band magnitudes up to 6.5 in the worst case and 4.5 in the best case. |
| TITLE: | Noise properties and signal-dependent interpixel crosstalk of the detectors of the Near-Infrared Spectrograph of the James Webb Space Telescope (Optical Engineering, SPIE, 2013) |
| AUTHOR(S): | Giovanna Giardino, Marco Sirianni, Stephan M. Birkmann et al. |
| ABSTRACT: | The Near-Infrared Spectrograph (NIRSpec) is one of the four science instruments of the James Webb Space Telescope. Its focal plane consists of two HAWAII-2RG sensors operating in the wavelength range of 0.6 to 5.0 μm and, as part of characterizing NIRSpec, the noise properties of these detectors under dark and illuminated conditions were studied. Under dark conditions, and as already known, 1/f noise in the detector system causes somewhat higher noise levels than can be accounted for by a simple model that includes white read noise and shot noise on integrated charge. More surprisingly, for high levels of accumulated charge, significantly lower total noise than expected was observed. This effect is shown to be due to pixel-to-pixel correlations introduced by signal-dependent interpixel crosstalk, with an interpixel coupling factor, α, that ranges from ˜0.01 for zero signal to ˜0.03 close to saturation.
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| TITLE: | The JWST near-infrared spectrograph NIRSpec: status (presented at SPIE 2012) |
| AUTHOR(S): | Pierre Ferruit, Giorgio Bagnasco, Reiner Barho et al. |
| ABSTRACT: | The Near-Infrared Spectrograph NIRSpec is one of the four instruments of the James Webb Space Telescope (JWST). NIRSpec will cover the 0.6-5.0 micron range and will be capable of obtaining spectra of more than 100 objects simultaneously in its multi-object spectroscopy (MOS) mode. It also features a set of slits and an aperture for high contrast spectroscopy of individual sources, as well as an integral-field unit (IFU) for 3D spectroscopy. We will first show how these capabilities are linked to the four main JWST scientific themes. We will then give an overview of the NIRpec modes and spectral configurations with an emphasis on the layout of the field of view and of the spectra. Last, we will provide an update on the status of the instrument. |
| TITLE | The Near Infrared Spectrograph (NIRSpec) on-ground calibration campaign (presented at SPIE 2012) |
| AUTHOR(S): | Stephan M. Birkmann, Pierre Ferruit, Torsten Böker et al. |
| ABSTRACT: | The Near Infrared Spectrograph (NIRSpec) is one of four science instruments aboard the James Webb Space Telescope (JWST) scheduled for launch in 2018. NIRSpec is sensitive in the wavelength range from ~0.6 to 5.0 micron and will be capable of obtaining spectra from more than a 100 objects simultaneously by means of a programmable micro shutter array. It will also provide an integral eld unit for 3D spectroscopy and xed slits for high contrast spectroscopy of individual sources and planet transit observations. We present results obtained during the rst cryogenic instrument testing in early 2011, demonstrating the excellent optical performance of the instrument. We also describe the planning of NIRSpecs forthcoming second calibration campaign scheduled for early 2013. |
| TITLE: | The accuracy of the NIRSpec grating wheel position sensors (presented at SPIE 2012) |
| AUTHOR(S): | Guido De Marchi, Stephan M. Birkmann, Torsten Böker et al. |
| ABSTRACT: | We present a detailed analysis of measurements collected during the first ground-based cryogenic calibration campaign of NIRSpec, the Near-Infrared Spectrograph for the James Webb Space Telescope (JWST). In this paper we concentrate on the performances of the NIRSpec grating wheel, showing that the magneto-resistive position sensors installed on the wheel provide very accurate information on the position of the wheel itself, thereby enabling an efficient acquisition of the science targets and a very accurate extraction and calibration of their spectra. |
| TITLE: | The spectro-photometric calibration of the JWST NIRSpec instrument (presented at SPIE 2012) |
| AUTHOR(S): | Torsten Böker, Stephan M. Birkmann, Guido De Marchi et al. |
| ABSTRACT: | NIRSpec is the main near-infrared spectrograph on board the James Webb Space Telescope, offering multi-object capabilities as well as an integral field unit and a number of fixed slits for studies of individual objects. In this paper, we describe the unique challenges in calibrating this complex instrument, and the approach taken to deal with them, both in terms of operational procedures and via automated processing of NIRSpec data. We provide a high-level description of the sequence of processing steps required for NIRSpec science data, and the necessary on-ground calibration files. We focus our discussion on the case of a typical multi-object observation with the MSA, in which adjacent micro-shutters are used to sample the science object and the sky background in an alternating way. This dithering strategy is particularly well suited for faint targets, but its guiding principles also apply to other NIRSpec modes. |
| TITLE: | NIRSpec detectors: noise properties and the effect of signal dependent inter-pixel crosstalk (presented as SPIE 2012) |
| AUTHOR(S): | Giardino Giovanna, Marco Sirianni, Stephan M. Birkmann et al. |
| ABSTRACT: | NIRSpec (Near Infrared Spectrograph) is one of the four science instruments of the James Webb Space Telescope (JWST) and its focal plane consists of two HAWAII-2RG sensors operating in the wavelength range 0.6-5.0μm. As part of characterizing NIRSpec, we studied the noise properties of these detectors under dark and illuminated conditions. Under dark conditions, and as already known, 1/f noise in the detector system produces somewhat more noise than can be accounted for by a simple model that includes white read noise and shot noise on integrated charge. More surprisingly, at high flux, we observe significantly lower total noise levels than expected. We show this effect to be due to pixel-to-pixel correlations introduced by signal dependent inter-pixel crosstalk, with an inter-pixel coupling factor, α, that ranges from ~ 0.01 for zero signal to ~ 0.03 close to saturation. |
| TITLE: | Wavelength calibration of the JWST Near Infrared Spectrograph (NIRSpec) |
| AUTHOR(S): | Stephan M. Birkmann, Torsten Böker, Pierre Ferruit, et al. |
| ABSTRACT: | The Near Infrared Spectrograph (NIRSpec) is one of four science instruments aboard the James Webb Space Telescope (JWST) that is to be launched later this decade. NIRSpec is sensitive in the wavelength range from 0.6 to 5.0 μm and operates at temperatures < 40K. It offers multi-object, fixed slit, and integral field spectroscopy with seven selectable dispersers. The on-ground spectrophotometric calibration of the instrument is performed by means of continuum and line emission lamps. NIRSpec also contains an internal calibration assembly (CAA) that will provide the wavelength and radiometric calibration in orbit. Due to thermal constraints, the CAA features low power tungsten filament lamps in combination with long-pass and Fabry-Perot-like interference filters, which need to be calibrated at instrument level. We will report on the wavelength calibration of the NIRSpec flight model and the CAA, carried out during the first cryogenic performance testing. |
| TITLE: | Calibrating the position of images and spectra in the NIRSpec instrument for the James Webb Space Telescope (presented as SPIE 2011) |
| AUTHOR(S): | Guido De Marchi, Maurice te Plate, Stephan M. Birkmann, et al. |
| ABSTRACT: | The Near Infrared Spectrograph (NIRSpec) is one of four science instruments on board the James Webb Space Telescope (JWST). NIRSpec offers multi-object, fixed slit, and integral field spectroscopy. There are eight optical elements mounted on the grating wheel assembly (GWA), six gratings, a double-pass prism, and a mirror. The precise knowledge of the position and tilt of these elements is critical for target acquisition and an accurate extraction and calibration of science data. We present the concept of calibrating the position/tilt sensors during the NIRSpec flight model ground calibration campaign, the performance of the sensors and first results concerning the GWA repeatability. |
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| TITLE: | Status of the NIRSpec Instrument (presented at SPIE 2010) |
| AUTHOR(S): | Stephan M. Birkmann, Torsten Böker, Peter Jakobsen, et al. |
| ABSTRACT: | The Near Infrared Spectrograph (NIRSpec) is one of the four science instruments aboard the James Webb Space Telescope (JWST) scheduled for launch in 2014. NIRSpec is sensitive in the wavelength range from ∼ 0.6 to 5.0 μm and will be capable of obtaining spectra of more than a 100 objects simultaneously, as well as fixed slit high contrast spectroscopy of individual sources. It also features an integral field unit for 3D spectroscopy. The key scientific objectives of the instrument include studies of star formation and chemical abundances of young distant galaxies and tracing the creation of the chemical elements back in time. In this paper, we present the status of the NIRSpec instrument as it is currently being prepared for its extensive ground calibration campaign later in 2010. |