Giovanna Giardino

Observations of Transiting Exoplanets with the James Webb Space Telescope (JWST)

This article summarizes a workshop held on March, 2014, on the potential of the James Webb Space Telescope (JWST) to revolutionize our knowledge of the physical properties of exoplanets through transit observations. JWSTs unique combination of high sensitivity and broad wavelength coverage will enable the accurate measurement of transits with high signal-to-noise. Most importantly, JWST spectroscopy will investigate planetary atmospheres to determine atomic and molecular compositions, to probe vertical and horizontal structure, and to follow dynamical evolution, i.e. exoplanet weather. JWST will sample a diverse population of planets of varying masses and densities in a wide variety of environments characterized by a range of host star masses and metallicities, orbital semi-major axes and eccentricities. A broad program of exoplanet science could use a substantial fraction of the overall JWST mission.

The JWST near-infrared spectrograph NIRSpec: status

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.

Status of the JWST/NIRSpec instrument

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.

Noise properties and signal-dependent interpixel crosstalk of the detectors of the Near-Infrared Spectrograph of the James Webb Space Telescope

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.

The accuracy of the NIRSpec grating wheel position sensors

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.

The Near Infrared Spectrograph (NIRSpec) on-ground calibration campaign

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.

NIRSpec detectors: noise properties and the effect of signal dependent inter-pixel crosstalk

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.

The JWST/NIRSpec instrument: update on status and performances

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 is developed by the European Space Agency (ESA) with Airbus Defense and 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. NIRSpec will be capable of obtaining spectra for more than 100 objects simultaneously using an array of micro-shutters. It also features an integral field unit with 3” x 3” field of view and a range of slits for high contrast spectroscopy of individual objects and time series observations of e.g. transiting exoplanets. NIRSpec is 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 ISIM level test campaign.

The JWST/NIRSpec exoplanet exposure time calculator

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.

Preparing the NIRSpec/JWST science data calibration: from ground testing to sky

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.