Publications of the Astronomical Society of the Pacific

Wright, G. S.; Wright, David; Goodson, G. B.; Rieke, G. H.; Aitink-Kroes, Gabby; Amiaux, J.; Aricha-Yanguas, Ana; Azzollini, Ruymán; Banks, Kimberly; Barrado-Navascues, D.; Belenguer-Davila, T.; Bloemmart, J. A. D. L.; Bouchet, Patrice; Brandl, B. R.; Colina, L.; Detre, Örs; Diaz-Catala, Eva; Eccleston, Paul; Friedman, Scott D.; García-Marín, Macarena; Güdel, Manuel; Glasse, Alistair; Glauser, Adrian M.; Greene, T. P.; Groezinger, Uli; Grundy, Tim; Hastings, Peter; Henning, Th.; Hofferbert, Ralph; Hunter, Faye; Jessen, N. C.; Justtanont, K.; Karnik, Avinash R.; Khorrami, Mori A.; Krause, Oliver; Labiano, Alvaro; Lagage, P.-O.; Langer, Ulrich; Lemke, Dietrich; Lim, Tanya; Lorenzo-Alvarez, Jose; Mazy, Emmanuel; McGowan, Norman; Meixner, M. E.; Morris, Nigel; Morrison, Jane E.; Müller, Friedrich; Nø rgaard-Nielson, H.-U.; Olofsson, Göran; O’Sullivan, Brian; Pel, J.-W.; Penanen, Konstantin; Petach, M. B.; Pye, J. P.; Ray, T. P.; Renotte, Etienne; Renouf, Ian; Ressler, M. E.; Samara-Ratna, Piyal; Scheithauer, Silvia; Schneider, Analyn; Shaughnessy, Bryan; Stevenson, Tim; Sukhatme, Kalyani; Swinyard, Bruce; Sykes, Jon; Thatcher, John; Tikkanen, Tuomo; van Dishoeck, E. F.; Waelkens, C.; Walker, Helen; Wells, Martyn; Zhender, Alex

doi: 10.1086/682253pmid: N/A

The Mid-InfraRed Instrument (MIRI) on the James Webb Space Telescope (JWST) provides measurements over the wavelength range 5 to 28.5 μm. MIRI has, within a single “package,” four key scientific functions: photometric imaging, coronagraphy, single-source low-spectral resolving power (R ∼ 100) spectroscopy, and medium-resolving power (R ∼ 1500 to 3500) integral field spectroscopy. An associated cooler system maintains MIRI at its operating temperature of < 6.7 K. This paper describes the driving principles behind the design of MIRI, the primary design parameters, and their realization in terms of the “as-built” instrument. It also describes the test program that led to delivery of the tested and calibrated Flight Model to NASA in 2012, and the confirmation after delivery of the key interface requirements.

Bouchet, Patrice; García-Marín, Macarena; Lagage, P.-O.; Amiaux, Jérome; Auguéres, J.-L.; Bauwens, Eva; Blommaert, J. A. D. L.; Chen, C. H.; Detre, Ö. H.; Dicken, Dan; Dubreuil, D.; Galdemard, Ph.; Gastaud, R.; Glasse, A.; Gordon, K. D.; Gougnaud, F.; Guillard, Phillippe; Justtanont, K.; Krause, Oliver; Leboeuf, Didier; Longval, Yuying; Martin, Laurant; Mazy, Emmanuel; Moreau, Vincent; Olofsson, Göran; Ray, T. P.; Rees, J.-M.; Renotte, Etienne; Ressler, M. E.; Ronayette, Samuel; Salasca, Sophie; Scheithauer, Silvia; Sykes, Jon; Thelen, M. P.; Wells, Martyn; Wright, David; Wright, G. S.

doi: 10.1086/682254pmid: N/A

In this article, we describe the Mid-Infrared Imager Module (MIRIM), which provides broadband imaging in the 5–27 μm wavelength range for the James Webb Space Telescope. The imager has a pixel scale and a total unobstructed view of 74″ × 113″. The remainder of its nominal 113″ × 113″ field is occupied by the coronagraphs and the low-resolution spectrometer. We present the instrument optical and mechanical design. We show that the test data, as measured during the test campaigns undertaken at CEA-Saclay, at the Rutherford Appleton Laboratory, and at the NASA Goddard Space Flight Center, indicate that the instrument complies with its design requirements and goals. We also discuss the operational requirements (multiple dithers and exposures) needed for optimal scientific utilization of the MIRIM.

Kendrew, Sarah; Scheithauer, Silvia; Bouchet, Patrice; Amiaux, Jerome; Azzollini, Ruymán; Bouwman, Jeroen; Chen, C. H.; Dubreuil, D.; Fischer, Sebastian; Glasse, Alistair; Greene, T. P.; Lagage, P.-O.; Lahuis, Fred; Ronayette, Samuel; Wright, David; Wright, G. S.

doi: 10.1086/682255pmid: N/A

The low-resolution spectrometer of the MIRI, which forms part of the imager module, will provide R ∼ 100 long-slit and slitless spectroscopy from 5 to 12 μm. The design is optimized for observations of compact sources, such as exoplanet host stars. We provide here an overview of the design of the LRS, and its performance as measured during extensive test campaigns, examining in particular the delivered image quality, dispersion, and resolving power, as well as spectrophotometric performance, flatfield accuracy, and the effects of fringing. We describe the operational concept of the slitless mode, which is optimally suited to transit spectroscopy of exoplanet atmospheres. The LRS mode of the MIRI was found to perform consistently with its requirements and goals.

Boccaletti, A.; Lagage, P.-O.; Baudoz, P.; Beichman, C.; Bouchet, P.; Cavarroc, C.; Dubreuil, D.; Glasse, Alistair; Glauser, A. M.; Hines, D. C.; Lajoie, C.-P.; Lebreton, J.; Perrin, M. D.; Pueyo, L.; Reess, J. M.; Rieke, G. H.; Ronayette, S.; Rouan, D.; Soummer, R.; Wright, G. S.

doi: 10.1086/682256pmid: N/A

The imaging channel on the Mid-Infrared Instrument (MIRI) is equipped with four coronagraphs that provide high-contrast imaging capabilities for studying faint point sources and extended emission that would otherwise be overwhelmed by a bright point-source in its vicinity. Such targets might include stars that are orbited by exoplanets and circumstellar material, mass-loss envelopes around post-main-sequence stars, the near-nuclear environments in active galaxies, and the host galaxies of distant quasars. This paper describes the coronagraphic observing modes of MIRI, as well as performance estimates based on measurements of the MIRI flight model during cryo-vacuum testing. A brief outline of coronagraphic operations is also provided. Finally, simulated MIRI coronagraphic observations of a few astronomical targets are presented for illustration.

Wells, Martyn; Pel, J.-W.; Glasse, Alistair; Wright, G. S.; Aitink-Kroes, Gabby; Azzollini, Ruymán; Beard, Steven; Brandl, B. R.; Gallie, Angus; Geers, V. C.; Glauser, A. M.; Hastings, Peter; Henning, Th.; Jager, Rieks; Justtanont, K.; Kruizinga, Bob; Lahuis, Fred; Lee, David; Martinez-Delgado, I.; Martínez-Galarza, J. R.; Meijers, M.; Morrison, Jane E.; Müller, Friedrich; Nakos, Thodori; O’Sullivan, Brian; Oudenhuysen, Ad; Parr-Burman, P.; Pauwels, Evert; Rohloff, R.-R.; Schmalzl, Eva; Sykes, Jon; Thelen, M. P.; van Dishoeck, E. F.; Vandenbussche, Bart; Venema, Lars B.; Visser, Huib; Waters, L. B. F. M.; Wright, David

doi: 10.1086/682281pmid: N/A

We describe the design and performance of the Medium Resolution Spectrometer (MRS) for the JWST-MIRI instrument. The MRS incorporates four coaxial spectral channels in a compact opto-mechanical layout that generates spectral images over fields of view up to 7.7 × 7.7″ in extent and at spectral resolving powers ranging from 1300 to 3700. Each channel includes an all-reflective integral field unit (IFU): an “image slicer” that reformats the input field for presentation to a grating spectrometer. Two 1024 × 1024 focal plane detector arrays record the output spectral images with an instantaneous spectral coverage of approximately one third of the full wavelength range of each channel. The full 5–28.5 μm spectrum is then obtained by making three exposures using gratings and pass-band-determining filters that are selected using just two three-position mechanisms. The expected on-orbit optical performance is presented, based on testing of the MIRI Flight Model and including spectral and spatial coverage and resolution. The point spread function of the reconstructed images is shown to be diffraction limited and the optical transmission is shown to be consistent with the design expectations.

Rieke, G. H.; Ressler, M. E.; Morrison, Jane E.; Bergeron, L.; Bouchet, Patrice; García-Marín, Macarena; Greene, T. P.; Regan, M. W.; Sukhatme, K. G.; Walker, Helen

doi: 10.1086/682257pmid: N/A

The MIRI Si:As IBC detector arrays extend the heritage technology from the Spitzer IRAC arrays to a 1024 × 1024 pixel format. We provide a short discussion of the principles of operation, design, and performance of the individual MIRI detectors, in support of a description of their operation in arrays provided in an accompanying paper. We then describe modeling of their response. We find that electron diffusion is an important component of their performance, although it was omitted in previous models. Our new model will let us optimize the bias voltage while avoiding avalanche gain. It also predicts the fraction of the IR-active layer that is depleted (and thus contributes to the quantum efficiency) as signal is accumulated on the array amplifier. Another set of models accurately predicts the nonlinearity of the detector-amplifier unit and has guided determination of the corrections for nonlinearity. Finally, we discuss how diffraction at the interpixel gaps and total internal reflection can produce the extended cross-like artifacts around images with these arrays at short wavelengths, ∼5 μm. The modeling of the behavior of these devices is helping optimize how we operate them and also providing inputs to the development of the data pipeline.

Ressler, M. E.; Sukhatme, K. G.; Franklin, B. R.; Mahoney, J. C.; Thelen, M. P.; Bouchet, P.; Colbert, J. W.; Cracraft, Misty; Dicken, D.; Gastaud, R.; Goodson, G. B.; Eccleston, Paul; Moreau, V.; Rieke, G. H.; Schneider, Analyn

doi: 10.1086/682258pmid: N/A

We describe the layout and unique features of the focal plane system for MIRI. We begin with the detector array and its readout integrated circuit (combining the amplifier unit cells and the multiplexer), the electronics, and the steps by which the data collection is controlled and the output signals are digitized and delivered to the JWST spacecraft electronics system. We then discuss the operation of this MIRI data system, including detector readout patterns, operation of subarrays, and data formats. Finally, we summarize the performance of the system, including remaining anomalies that need to be corrected in the data pipeline.

Glasse, Alistair; Rieke, G. H.; Bauwens, E.; García-Marín, Macarena; Ressler, M. E.; Rost, Steffen; Tikkanen, T. V.; Vandenbussche, B.; Wright, G. S.

doi: 10.1086/682259pmid: N/A

We present an estimate of the performance that will be achieved during on-orbit operations of the JWST mid-infrared instrument, MIRI. The efficiency of the main imager and spectrometer systems in detecting photons from an astronomical target are presented, based on measurements at subsystem and instrument-level testing, with the end-to-end transmission budget discussed in some detail. The brightest target fluxes that can be measured without saturating the detectors are provided. The sensitivity for long-duration observations of faint sources is presented in terms of the target flux required to achieve a signal-to-noise ratio of 10 after a 10,000 s observation. The algorithms used in the sensitivity model are presented, including the understanding gained during testing of the MIRI flight model and flight-like detectors.