We describe here the performance and operational concept for the Low Resolution Spectrometer (LRS) of the mid-infrared instrument (MIRI) for the James Webb Space Telescope. The LRS will provide R∼100 slit and
slitless spectroscopy from 5 to 12 micron, and its design is optimised 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. The instrument also includes a slitless spectroscopy mode, which is optimally suited for transit spectroscopy of exoplanet atmospheres. We provide an overview of the operational procedures and the differences ahead of the JWST launch in 2018.
The Mid-Infrared Instrument (MIRI) Medium Resolution Spectrometer (MRS) is the only mid-IR Integral Field Spectrometer on board James Webb Space Telescope. The complexity of the MRS requires a very specialized pipeline, with some specific steps not present in other pipelines of JWST instruments, such as fringe corrections and wavelength offsets, with different algorithms for point source or extended source data. The MRS pipeline has also two different variants: the baseline pipeline, optimized for most foreseen science cases, and the optimal pipeline, where extra steps will be needed for specific science cases. This paper provides a comprehensive description of the MRS Calibration Pipeline from uncalibrated slope images to final scientific products, with brief descriptions of its algorithms, input and output data, and the accessory data and calibration data products necessary to run the pipeline.
Significant improvements in our understanding of various photometric effects have occurred in the more than nine years
of flight operations of the Infrared Array Camera aboard the Spitzer Space Telescope. With the accumulation of
calibration data, photometric variations that are intrinsic to the instrument can now be mapped with high fidelity. Using
all existing data on calibration stars, the array location-dependent photometric correction (the variation of flux with
position on the array) and the correction for intra-pixel sensitivity variation (pixel-phase) have been modeled
simultaneously. Examination of the warm mission data enabled the characterization of the underlying form of the pixelphase
variation in cryogenic data. In addition to the accumulation of calibration data, significant improvements in the
calibration of the truth spectra of the calibrators has taken place. Using the work of Engelke et al. (2006), the KIII
calibrators have no offset as compared to the AV calibrators, providing a second pillar of the calibration scheme. The
current cryogenic calibration is better than 3% in an absolute sense, with most of the uncertainty still in the knowledge of
the true flux densities of the primary calibrators. We present the final state of the cryogenic IRAC calibration and a
comparison of the IRAC calibration to an independent calibration methodology using the HST primary calibrators.
One of the goals of the operations system being developed at the Space Telescope Science Institute for the
James Webb Space Telescope (JWST) is to produce the most efficient use of the observatory that is scientifically
justified. To first order, this means maximizing the amount of time spent collecting photons on science targets
while ensuring the health and safety of the observatory and obtaining the necessary calibration data. We present
recent efforts by the JWST EfficiencyWorking Group at STScI to quantify the expected observing efficiency based
on current plans for the operations system. These include collecting the expected observatory and instrument
overheads and updating a set of prototypical observing programs that will approximate over one full year of
JWST observations. The combination of these two efforts is being used to investigate the expected observing
efficiency and determine revised strategies to minimize overheads and maximize this efficiency.
The Mid-Infrared Instrument (MIRI) is one of the three scientific instruments to fly on the James Webb Space
Telescope (JWST), which is due for launch in 2013. MIRI contains two sub-instruments, an imager, which has low
resolution spectroscopy and coronagraphic capabilities in addition to imaging, and a medium resolution IFU
spectrometer. A verification model of MIRI was assembled in 2007 and a cold test campaign was conducted between
November 2007 and February 2008. This model was the first scientifically representative model, allowing a first
assessment to be made of the performance. This paper describes the test facility and testing done. It also reports on the
first results from this test campaign.
The far-infrared detectors on the Multiband Imaging Photometer for Spitzer (MIPS) represent a significant advancement in both format and sensitivity. We describe some of the operational experience since launch in August 2003. MIPS has three infrared detector arrays, a 128x128 format Si:As impurity band conduction detector operating at 24 μm, a 32x32 format Ge:Ga array operating at 70 μm and a 2x20 format stressed Ge:Ga array operating at 160 μm. Since both germanium detectors utilize conventional bulk photoconductors, they are subject to a number of non-ideal behaviors
that are inherent in these types of devices when operated in ultra-low backgrounds. The principal problems are nonlinear time response, changing responsivity in a radiation environment, and flux non-linearities. We describe observing strategies that are used on MIPS to minimize the impact of these effects.
The first six months of flight data from the Multiband Imaging Photometer for Spitzer (MIPS) were used to test MIPS reduction algorithms based on extensive preflight laboratory data and modeling. The underlying approach for the preflight algorithms has been found to be sound, but some modifications have improved the performance.
The main changes are scan mirror dependent flat fields at 24 μm, hand processing to remove the time dependent stim flash latents and fast/slow response variations at 70 μm, and the use of asteroids and other sources instead of stars for flux calibration at 160 μm due to a blue "leak." The photometric accuracy of flux measurements is currently 5%, 10%, and 20% at 24, 70, and 160 μm, respectively. These numbers are expected to improve as more flight data are analyzed and data reduction algorithms refined.
The Multiband Imaging Photometer for Spitzer (MIPS) provides long wavelength capability for the mission, in imaging bands at 24, 70, and 160 microns and measurements of spectral energy distributions between 52 and 100 microns at a spectral resolution of about 7%. By using true detector arrays in each band, it provides both critical sampling of the Spitzer point spread function and relatively large imaging fields of view, allowing for substantial advances in sensitivity, angular resolution, and efficiency of areal coverage compared with previous space far-infrared capabilities. The Si:As BIB 24 micron array has excellent photometric properties, and measurements with rms relative errors of 1% or better can be obtained. The two longer wavelength arrays use Ge:Ga detectors with poor photometric stability. However, the use of 1.) a scan mirror to modulate the signals rapidly on these arrays, 2.) a system of on-board stimulators used for a relative calibration approximately every two minutes, and 3.) specialized reduction software result in good photometry with these arrays also, with rms relative errors of less than 10%.
We describe the ground testing and characterization of the Multiband Imaging Photometer for SIRTF (MIPS). This instrument is a camera with three focal plane arrays covering broad spectral bands centered at 24 μm, 70 μm, and 160 μm. The instrument features a variety of operation modes that permit accurate photometry, diffraction-limited imaging, efficient mapping, and low resolution spectral energy distribution determinations. The observational philosophy of MIPS relies heavily on the frequent use of internal relative calibration sources as well as a high level of redundancy in the data collection. We show that by using this approach, users of MIPS can expect very sensitive, highly repeatable observations of astronomical sources. The ground characterization program for MIPS involved a number of facilities including test dewars for focal-plane level testing, a specialized cryostat for instrument-level testing, and tests in the flight SIRTF Cryo-Telescope Assembly
We describe the test approaches and results for the Multiband Imaging Photometer for SIRTF. To verify the performance within a `faster, better, cheaper' budget required innovations in the test plan, such as heavy reliance on measurements with optical photons to determine instrument alignment, and use of an integrating sphere rather than a telescope to feed the completed instrument at its operating temperature. The tests of the completed instrument were conducted in a cryostat of unique design that allowed us to achieve the ultra-low background levels the instrument will encounter in space. We controlled the instrument through simulators of the mission operations control system and the SIRTF spacecraft electronics, and used cabling virtually identical to that which will be used in SIRTF. This realistic environment led to confidence in the ultimate operability of the instrument. The test philosophy allowed complete verification of the instrument performance and showed it to be similar to pre-integration predictions and to meet the instrument requirements.