for the James Webb Space Telescope
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Two NIRCam Channels Are Better Than One: How JWST Can Do More Science with NIRCam's Short-Wavelength Dispersed Hartmann Sensor
Schlawin et al
2018
NASA ADS
The James Webb Space Telescope (JWST) offers unprecedented sensitivity, stability, and wavelength coverage for transiting exoplanet studies, opening up new avenues for measuring atmospheric abundances, structure, and temperature profiles. Taking full advantage of JWST spectroscopy of planets from 0.6 μm to 28 μm, however, will require many observations with a combination of the NIRISS, NIRCam, NIRSpec, and MIRI instruments. In this white paper, we discuss a new NIRCam mode (not yet approved or implemented) that can reduce the number of necessary observations to cover the 1.0 μm to 5.0 μm wavelength range. Even though NIRCam was designed primarily as an imager, it also includes several grisms for phasing and aligning JWST's 18 hexagonal mirror segments. NIRCam's long-wavelength channel includes grisms that cover 2.4 μm to 5.0 μm with a resolving power of R = 1200 – 1550 using two separate configurations. The long-wavelength grisms have already been approved for science operations, including wide field and single object (time series) slitless spectroscopy. We propose a new mode that will simultaneously measure spectra for science targets in the 1.0 μm to 2.0 μm range using NIRCam's short-wavelength channel. This mode, if approved, would take advantage of NIRCam's Dispersed Hartmann Sensor (DHS), which produces 10 spatially separated spectra per source at R ~300. We discuss the added benefit of the DHS in constraining abundances in exoplanet atmospheres as well as its ability to observe the brightest systems. The DHS essentially comes for free (at no time cost) with any NIRCam long-wavelength grism observation, but the detector integration parameters have to be selected to ensure that the long-wavelength grism observations do not saturate and that JWST data volume downlink constraints are not violated. Combining both of NIRCam's channels will maximize the science potential of JWST, which is a limited life observatory.
Clear and Cloudy Exoplanet Forecasts for JWST: Maps, Retrieved Composition and Constraints on Formation with MIRI and NIRcam
Schlawin et al
2018
NASA ADS
The James Webb Space Telescope (JWST) will measure exoplanet transmission and eclipse spectroscopy at unprecedented precisions to better understand planet structure, dynamics, chemistry and formation. These are essential tools on the march toward biosignature searches on potentially habitable planets. We explore a range of exoplanet atmospheric conditions and forecast the expected results with JWST. We take realistic CHIMERA models that match existing Spitzer and HST results and simulate the spectra achievable with the JWST MIRI + NIRCam Guaranteed Time Observations (GTO) survey, which includes observations of HD 189733 b, WASP-80 b, HAT-P-19 b, WASP-107 b, GJ 436 b and HAT-P-26 b. We then retrieve atmospheric parameters from these spectra to estimate the precision to which the planets' atmospheric compositions can be measured. We find that emission spectra have well-constrained unimodal solutions but transmission spectra near 10x solar abundance and solar C/O ratios can suffer from bimodal solutions. Broad wavelength coverage as well as higher precision data can resolve bimodal solutions and provide dramatically better atmospheric parameter constraints. We find that metallicities can be measured to within 20% to 170%, which approaches the precisions on Solar System planets, and C/O ratios can be constrained to ~10% to 60%, assuming that observers can leverage short wavelength data to select the correct solution from the bimodal posteriors. These compositional precisions are sufficient to validate or refute predictions from disk formation models on final atmospheric abundances as long as their history is not erased by planet evolution processes. We also show the extent to which eclipse mapping with JWST is possible on our brightest system HD 189733 b.
NIRCam Coronagraphic Observations of Disks and Planetary Systems
Beichman et al
2017
NASA ADS
The NIRCam coronagraph offers a dramatic increase in sensitivity at wavelengths of 3-5 um where young planets are brightest. While large ground-based telescopes with Extreme Adaptive Optics have an advantage in inner working angle, NIRCam's sensitivity will allow high precision photometry for known planets and searches for planets with masses below that of Saturn. For debris disk science NIRCam observations will address the scattering properties of dust, look for evidence of ices and tholins, and search for planets which affect the structure of the disk itself. The NIRCam team's GTO program includes medium-band filter observations of known young planets having 1-5 Jupiter masses. A collaborative program with the MIRI team will provide coronagraphic observations at longer wavelengths. The combined dataset will yield the exoplanet’s total luminosity and effective temperature, an estimate of the initial entropy of the newly-formed planet, and the retrieval of atmospheric properties. The program will also make deep searches for lower mass planets toward known planetary systems, nearby young M stars and debris disk systems. Achievable mass limits range from ~1 Jupiter mass beyond 20 AU for the brightest A stars to perhaps a Uranus mass within 10 AU for the closest M stars. We will discuss details of the coronagraphic program for both the exoplanet and debris disk cases with an emphasis on using APT to optimize the observations of target and reference stars.
λ = 2.4 to 5 μm spectroscopy with the James Webb Space Telescope NIRCam instrument
Greene et al
2017
NASA ADS
The James Webb Space Telescope near-infrared camera (JWST NIRCam) has two 2.02 × 2.02 fields of view that can be observed with either imaging or spectroscopic modes. Either of two R ∼ 1500 grisms with orthogonal dispersion directions can be used for slitless spectroscopy over λ = 2.4 to 5.0 μm in each module, and shorter wavelength observations of the same fields can be obtained simultaneously. We describe the design drivers and parameters of the grisms and present the latest predicted spectroscopic sensitivities, saturation limits, resolving powers, and wavelength coverage values. Simultaneous short wavelength (0.6 to 2.3 μm) imaging observations of the 2.4 to 5.0 μm spectroscopic field can be performed in one of several different filter bands, either infocus or defocused via weak lenses internal to the NIRCam. The grisms are available for single object time-series spectroscopy and wide-field multiobject slitless spectroscopy modes in the first cycle of JWST observations. We present and discuss operational considerations including subarray sizes and data volume limits. Potential scientific uses of the grisms are illustrated with simulated observations of deep extragalactic fields, dark clouds, and transiting exoplanets. Information needed to plan observations using these spectroscopic modes is also provided.
Slitless Spectroscopy with the James Webb Space Telescope Near-Infrared Camera (JWST NIRCam)
Greene et al
2016
NASA ADS
The James Webb Space Telescope near-infrared camera (JWST NIRCam) has two 2.′2 × 2.′2 fields of view that are capable of either imaging or spectroscopic observations. Either of two R ∼ 1500 grisms with orthogonal dispersion directions can be used for slitless spectroscopy over λ = 2.4 − 5.0 μm in each module, and shorter wavelength observations of the same fields can be obtained simultaneously. We present the latest predicted grism sensitivities, saturation limits, resolving power, and wavelength coverage values based on component measurements, instrument tests, and end-to-end modeling. Short wavelength (0.6 – 2.3 μm) imaging observations of the 2.4 – 5.0 μm spectroscopic field can be performed in one of several different filter bands, either in-focus or defocused via weak lenses internal to NIRCam. Alternatively, the possibility of 1.0 – 2.0 μm spectroscopy (simultaneously with 2.4 – 5.0 μm) using dispersed Hartmann sensors (DHSs) is being explored. The grisms, weak lenses, and DHS elements were included in NIRCam primarily for wavefront sensing purposes, but all have significant science applications. Operational considerations including subarray sizes, and data volume limits are also discussed. Finally, we describe spectral simulation tools and illustrate potential scientific uses of the grisms by presenting simulated observations of deep extragalactic fields, galactic dark clouds, and transiting exoplanets.
Observations of Transiting Exoplanets with the James Webb Space Telescope (JWST)
Beichman et al
2014
NASA ADS
The study of exoplanets is called out explicitly in NASA’s Strategic Plan as one of NASA’s high level science goals: “Objective 1.6: Discover how the universe works, explore how it began and evolved, and search for life on planets around other stars.” The Strategic Plan calls out the James Webb Space Telescope (JWST) explicitly as a critical facility for studying exoplanets: “JWST will allow us to . . . study in detail planets around other stars.” The JWST project also cites exoplanet research among its most important goals: “The Birth of Stars and Protoplanetary systems focuses on the birth and early development of stars and the formation of planets... Planetary Systems and the Origins of Life studies the physical and chemical properties of solar systems (including our own) and where the building blocks of life may be present.” Now, with the construction of JWST well underway, the exoplanet community is starting to think in detail about how it will use JWST to advance specific scientific cases. [...]
Science Opportunities with the Near-IR Camera (NIRCam) on the James Webb Space Telescope (JWST)
Beichman et al
2012
NASA ADS
The Near-Infrared Camera (NIRCam) on the James Webb Space Telescope (JWST) offers revolutionary gains in sensitivity throughout the 1-5 μm region. NIRCam will enable great advances in all areas of astrophysics, from the composition of objects in our own Kuiper Belt and the physical properties of planets orbiting nearby stars to the formation of stars and the detection of the youngest galaxies in the Universe. NIRCam also plays an important role in initial alignment of JWST and the long term maintenance of its image quality. NIRCam is presently undergoing instrument Integration and Test in preparation for delivery to the JWST project. Key near-term milestones include the completion of cryogenic testing of the entire instrument; demonstration of scientific and wavefront sensing performance requirements; testing of replacement H2RG detectors arrays; and an analysis of coronagraphic performance in light of measured telescope wavefront characteristics. This paper summarizes the performance of NIRCam, the scientific and education/outreach goals of the science team, and some results of the on-going testing program.
Observing exoplanets with the JWST NIRCam grisms
Greene et al
2007
PDF
The near-infrared camera (NIRCam) on the James Webb Space Telescope (JWST) will incorporate 2 identical grisms in each of its 2 long wavelength channels. These transmission gratings have been added to assist with the coarse phasing of the JWST telescope, but they will also be used for slitless wide-field scientific observations over selectable regions of the λ = 2.4 – 5.0 μm wavelength range at spectroscopic resolution R ≡ λ/δλ ≃ 2000. We describe the grism design details and their expected performance in NIRCam. The grisms will provide point- source continuum sensitivity of approximately AB = 23 mag in 10,000 s exposures with S/N = 5 when binned to R = 1000. This is approximately a factor of 3 worse than expected for the JWST NIRSpec instrument, but the NIRCam grisms provide better spatial resolution, better spectrophotometric precision, and complete field coverage. The grisms will be especially useful for high precision spectrophotometric observations of transiting exoplanets. We expect that R = 500 spectra of the primary transits and secondary eclipses of Jupiter-sized exoplanets can be acquired at moderate or high signal-to-noise for stars as faint as M = 10 – 12 mag in 1000 s of integration time, and even bright stars (V = 5 mag) should be observable without saturation. We also discuss briefly how these observations will open up new areas of exoplanet science and suggest other unique scientific applications of the grisms.
Hunting Planets and Observing Disks with the JWST NIRCam Coronagraph
Krist et al
2007
NASA ADS
The near-infrared camera (NIRCam) on the James Webb Space Telescope (JWST) will incorporate 2 identical grisms in each of its 2 long wavelength channels. These transmission gratings have been added to assist with the coarse phasing of the JWST telescope, but they will also be used for slitless wide-field scientific observations over selectable regions of the λ = 2.4 – 5.0 µm wavelength range at spectroscopic resolution R ≡ λ/δλ " 2000. We describe the grism design details and their expected performance in NIRCam. The grisms will provide pointsource continuum sensitivity of approximately AB = 23 mag in 10,000 s exposures with S/N = 5 when binned to R = 1000. This is approximately a factor of 3 worse than expected for the JWST NIRSpec instrument, but the NIRCam grisms provide better spatial resolution, better spectrophotometric precision, and complete field coverage. The grisms will be especially useful for high precision spectrophotometric observations of transiting exoplanets. We expect that R = 500 spectra of the primary transits and secondary eclipses of Jupiter-sized exoplanets can be acquired at moderate or high signal-to-noise for stars as faint as M = 10 – 12 mag in 1000 s of integration time, and even bright stars (V = 5 mag) should be observable without saturation. We also discuss briefly how these observations will open up new areas of exoplanet science and suggest other unique scientific applications of the grisms.
High contrast imaging with the JWST NIRCAM coronagraph
Green et al
2005
NASA ADS
Relative to ground-based telescopes, the James Webb Space Telescope (JWST) will have a substantial sensitivity advantage in the 2.2-5 μm wavelength range where brown dwarfs and hot Jupiters are thought to have significant brightness enhancements. To facilitate high contrast imaging within this band, the Near-Infrared Camera (NIRCAM) will employ a Lyot coronagraph with an array of band-limited image-plane occulting spots. In this paper, we provide the science motivation for high contrast imaging with NIRCAM, comparing its expected performance to that of the Keck, Gemini and 30 m (TMT) telescopes equipped with Adaptive Optics systems of different capabilities. We then describe our design for the NIRCAM coronagraph that enables imaging over the entire sensitivity range of the instrument while providing significant operational flexibility. We describe the various design tradeoffs that were made in consideration of alignment and aberration sensitivities and present contrast performance in the presence of JWST's expected optical aberrations. Finally we show an example of a two-color image subtraction that can provide 10-5 companion sensitivity at sub-arcsecond separations.
SPIE Papers on NIRCam, presented August 2005
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