Explore the vast range of titles available.

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.

Spectra of young benchmark brown dwarfs with well-known ages are vital to characterize other brown dwarfs, for which ages are in general not known. These spectra are also crucial to test atmospheric models, which have the potential to provide detailed information about the atmospheres of these objects. However, to test atmospheric models optimally, medium-resolution, long-wavelength-coverage spectra with well-understood uncertainties are ideal, such as the spectra provided by the NIRSpec instrument on board the James Webb Space Telescope. In this paper, we present medium-resolution JWST/NIRSpec spectra of two young brown dwarfs, TWA 28 (M9.0) and TWA 27A (M9.0), and one planetary-mass object, TWA 27B (L6.0), members of the TW Hydrae Association (age ∼ 10 Myr). We show the richness of the atomic lines and molecular bands present in the spectra. All objects show signs of a circumstellar disk, via a near-infrared excess and/or via emission lines. We matched a set of cloudless atmospheric spectra (ATMO), and cloudy atmospheric spectra (BT-Settl) to our NIRSpec spectra, and analyzed which wavelength ranges and spectral features both models reproduce best. Both models derive consistent parameters for the three sources, and predict the existence of CH4 at 3.35 μm in TWA 27B. Nonetheless, in contrast to other slightly older objects with similar spectral type, like PSO 318.5–22 and VHS 1256b, this feature is not present in the spectrum of TWA 27B. The lack of the CH4 feature might suggest that the L–T transition of very young dwarfs starts at later spectral types than for older brown dwarfs.

We present 1–5 μm spectroscopy of the young planetary mass companion TWA 27B (2M1207B) performed with NIRSpec on board the James Webb Space Telescope. In these data, the fundamental band of CH4 is absent, and the fundamental band of CO is weak. The nondetection of CH4 reinforces a previously observed trend of weaker CH4 with younger ages among L dwarfs, which has been attributed to enhanced nonequilibrium chemistry among young objects. The weakness of CO may reflect an additional atmospheric property that varies with age, such as the temperature gradient or cloud thickness. We are able to reproduce the broad shape of the spectrum with an ATMO cloudless model that has T eff = 1300 K, nonequilibrium chemistry, and a temperature gradient reduction caused by fingering convection. However, the fundamental bands of CH4 and CO are somewhat stronger in the model. In addition, the model temperature of 1300 K is higher than expected from evolutionary models given the luminosity and age of TWA 27B (T eff = 1200 K). Previous models of young L-type objects suggest that the inclusion of clouds could potentially resolve these issues; it remains to be seen whether cloudy models can provide a good fit to the 1–5 μm data from NIRSpec. TWA 27B exhibits emission in Paschen transitions and the He I triplet at 1.083 μm, which are signatures of accretion that provide the first evidence of a circumstellar disk. We have used the NIRSpec data to estimate the bolometric luminosity of TWA 27B (log L/L ⊙ = −4.466 ± 0.014), which implies a mass of 5–6 M Jup according to evolutionary models.

We examine cosmic‐ray rejection methodology on data collected from InSb and Si:As detectors. The application of an up‐the‐ramp sampling technique with cosmic‐ray identification and mitigation is the focus of this study. This technique is valuable for space‐based observatories which are exposed to high‐radiation environments. We validate the up‐the‐ramp approach on radiation‐test data sets with InSb and Si:As detectors which were generated for SIRTF. The up‐the‐ramp sampling method studied in this paper is over 99.9% effective at removing cosmic rays and preserves the structure and photometric quality of the image to well within the measurement error.

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.

We present 1-5um spectroscopy of the young planetary mass companion TWA 27B (2M1207B) performed with NIRSpec on board the James Webb Space Telescope. In these data, the fundamental band of CH_4 is absent and the fundamental band of CO is weak. The nondetection of CH_4 reinforces a previously observed trend of weaker CH_4 with younger ages among L dwarfs, which has been attributed to enhanced non-equilibrium chemistry among young objects. The weakness of CO may reflect an additional atmospheric property that varies with age, such as the temperature gradient or cloud thickness. We are able to reproduce the broad shape of the spectrum with an ATMO cloudless model that has T=1300 K, non-equilibrium chemistry, and a temperature gradient reduction caused by fingering convection. However, the fundamental bands of CH_4 and CO are somewhat stronger in the model. In addition, the model temperature of 1300 K is higher than expected from evolutionary models given the luminosity and age of TWA 27B (T=1200 K). Previous models of young L-type objects suggest that the inclusion of clouds could potentially resolve these issues; it remains to be seen whether cloudy models can provide a good fit to the 1-5um data from NIRSpec. TWA 27B exhibits emission in Paschen transitions and the He I triplet at 1.083um, which are signatures of accretion that provide the first evidence of a circumstellar disk. We have used the NIRSpec data to estimate the bolometric luminosity of TWA 27B (log L/L_sun=-4.466+/-0.014), which implies a mass of 5-6 MJup according to evolutionary models.

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 (H2RG) detectors, wheel mechanisms, and the micro-shutter 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 spectro-photometric 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.

We provide an overview of the design and capabilities of the near-infrared spectrograph (NIRSpec) onboard the James Webb Space Telescope. NIRSpec is designed to be capable of carrying out low-resolution (\\(R\\!=30\\!-330\\)) prism spectroscopy over the wavelength range \\(0.6-5.3\\!~\\)m and higher resolution (\\(R\\!=500\\!-1340\\) or \\(R\\!=1320\\!-3600\\)) grating spectroscopy over \\(0.7-5.2\\!~\\)m, both in single-object mode employing any one of five fixed slits, or a 3.1\\(\\)3.2 arcsec\\(^2\\) integral field unit, or in multiobject mode employing a novel programmable micro-shutter device covering a 3.6\\(\\)3.4~arcmin\\(^2\\) field of view. The all-reflective optical chain of NIRSpec and the performance of its different components are described, and some of the trade-offs made in designing the instrument are touched upon. The faint-end spectrophotometric sensitivity expected of NIRSpec, as well as its dependency on the energetic particle environment that its two detector arrays are likely to be subjected to in orbit are also discussed.

The Near-Inrared Spectrograph (NIRSpec) on the James Webb Space Telescope (JWST) is a very versatile instrument, offering multiobject and integral field spectroscopy with varying spectral resolution (\\(\\)30 to \\(\\)3000) over a wide wavelength range from 0.6 to 5.3 micron, enabling scientists to study many science themes ranging from the first galaxies to bodies in our own Solar System. In addition to its integral field unit and support for multiobject spectroscopy, NIRSpec features several fixed slits and a wide aperture specifically designed to enable high precision time-series and transit as well as eclipse observations of exoplanets. In this paper we present its capabilities regarding time-series observations, in general, and transit and eclipse spectroscopy of exoplanets in particular. Due to JWST's large collecting area and NIRSpec's excellent throughput, spectral coverage, and detector performance, this mode will allow scientists to characterize the atmosphere of exoplanets with unprecedented sensitivity.

The focal plane of the NIRSpec instrument on board the James Webb Space Telescope (JWST) is equipped with two Teledyne H2RG near-IR detectors, state-of-the-art HgCdTe sensors with excellent noise performance. Once JWST is in space, however, the noise level in NIRSpec exposures will be affected by the cosmic ray (CR) fluence at the JWST orbit and our ability to detect CR hits and to mitigate their effect. We have simulated the effect of CRs on NIRSpec detectors by injecting realistic CR events onto dark exposures that were recently acquired during the JWST cryo-vacuum test campaign undertaken at Johnson Space Flight Center. Here we present the method we have implemented to detect the hits in the exposure integration cubes, to reject the affected data points within our ramp-to-slope processing pipeline (the prototype of the NIRSpec official pipeline), and assess the performance of this method for different choices of the algorithm parameters. Using the optimal parameter set to reject CR hits from the data, we estimate that, for an exposure length of 1,000 s, the presence of CRs in space will lead to an increase of typically ~7% in the detector noise level with respect to the on-ground performance, and the corresponding decrease in the limiting sensitivity of the instrument, for the medium and high-spectral resolution modes.