Cycle 1 Calibration - MIRI
The activities listed below are those parts of the Cycle 1 Calibration plan for the Mid Infrared Instrument (MIRI) that have a dedicated observational component. It is important to remember that the Cycle 1 Calibration plan is not final. The plan as laid out here is based on our current understanding of the telescope, instruments, and all other planned observations in Cycle 1. This program should be considered provisional and may change in response to system developments and the final science program.
The text for each calibration activity below includes a title, program ID number, and the abstract also included with the APT file. The program ID number links directly to the STScI webpage for that program. Users interested in obtaining APT files can either follow that link or retrieve the file by running the APT and retrieving it by its program ID.
Program 1517 - CAL-MIRI-001 - Read Noise and Dark Current Monitoring
This activity will obtain calibration data for all three MIRI detectors early in Cycle 1 to address three issues that will set the ultimate sensitivity limit for MIRI: read noise, dark current, and the reset anomaly, including the non-ideal behavior of individual integration ramps caused by the reset. All three effects require reference files for each detector in the JWST calibration pipeline. The data will also be used to flag hot, dead, and high-noise pixels for the bad-pixel mask. The activity will produce a full suite of data including simultaneous data from the full imager detector and the two MRS detectors with the contamination control cover (CCC) closed and data in all of the available subarrays except SLITLESSPRISM with the CCC open.
Program 1518 - CAL-MIRI-002 - Internal Flat Monitor
During the course of the JWST mission, small changes can be expected in the detector operating parameters (especially bias voltage and temperature). Additionally, space weathering from the cumulative impacts of cosmic rays will slowly degrade detector properties. As a result, we can fully expect that detector responsivities will change with time, making it imperative that we monitor the MIRI detectors on a regular basis and have the data available to develop new flatfields when they are required. Periodic (monthly) measurements of the on-board calibration sources plus background sky are intended to provide the following information: (1) Tracking of trends and changes in the relative radiometric response of the imager and Medium Resolution Spectrometer (MRS) for the optical train between the calibration source and the detector. (2) When combined with measurements of photometric standard stars, the ability to derive the absolute radiometric response at all times and all points in the field of the imager and MRS. (3) The pixel flat field (gain or responsivity matrix). (4) High signal-to-noise measurements of the MRS spectral fringes.
Program 1519 - CAL-MIRI-003 - RSCD Characterization
The MIRI detectors must be calibrated for a variety of effects, including the reset switch charge decay (RSCD). The RSCD leads to a difference between the slope of the first integration in a series compared to later integrations, and it depends significantly on the illumination level of the previous integration. This calibration activity obtains data to characterize the RSCD an d improve the corrective algorithms applied by the calibration pipeline. By using the MIRI internal calibration lamps with different imaging filters and in the three MRS grating settings, we will obtain a variety of illumination levels. These data will be combined with darks to constrain and improve the correction algorithm.
Program 1520 - CAL-MIRI-007 - Detector Anneals
This calibration activity will routinely anneal the three MIRI detectors to remove detector artifacts and keep the detector arrays in a known and stable state. With our current knowledge of the behavior of the MIRI detectors, we estimate that a frequency of once-a-day anneals will be sufficient to ensure good detector performance during Cycle 1. The anneals will be performed during spacecraft slews and will use the optimum temperature set-point determined during commissioning activity CAR-MIRI-002.
Program 1521 - CAL-MIRI-012 - Imaging External Flatfield
This activity will obtain external flat fields at low spatial frequencies (L-flats) for the MIRI imager. It builds on the commissioning activity CAR-MIRI-053. We will use the “thousand-points-of-light” technique to measure the L-flats by observing the LMC astrometric field with a dither pattern designed to sample the same stars in multiple positions on the detector. The data obtained in this activity will also be used to monitor geometric distortion and boresight offset corrections (CAL-MIRI-016). These data will also help monitor the shape of the core of the PSF across the detector (CAL-MIRI-014). This activity will be executed once in Cycle 1 in month 3, so that it occurs relatively early in Cycle 1 but still provides a reasonable temporal baseline from the related activity during commissioning.
Program 1522 - CAL-MIRI-018 - Imaging Filter Characterization
This activity will test the ground-based filter transmission functions by observing a red object through all nine MIRI imaging filters. The target will be a main-belt asteroid which will also be observed with the MRS to provide a spectrum covering the full 5-28 um wavelength range. Comparing synthetic photometry of the asteroid using the MRS spectrum of the asteroid with the actual photometry with the imager will test the filter functions and check for any possible filter leaks of red or blue light. Similar analysis on standard stars, comparing actual photometry and synthetic photometry with both model spectra and MRS spectra will provide further tests. This activity will be performed jointly with CAL-NIS-024; combining the observations may lead to some savings compared to the quoted time requirement.
Program 1523 - CAL-MIRI-022- MRS External Flatfield
This activity performs external flatfields (illumination flats) to provide low-spatial-frequency flatfields (L-flats) for the MIRI MRS. The data provided will probe the overall system transmission and illumination of the detectors, as a function of position in the focal plane, wavelength, and the resulting map onto position on the detectors. Repeating the similar observations obtained in commissioning (CAR-MIRI-061) will provide a valuable check on the stability of system transmission and pixel responsivity and, with the added integration time, improve the signal-noise-ratio (SNR) of the resultant L-flat. The first choice for a target is a nearby extended planetary nebula NGC 7027.
Program 1524 - CAL-MIRI-024 - MRS PSF Characterization
This activity will characterize the point spread functions (PSFs) in the MIRI medium resolution spectrometer (MRS). The primary goals are to measure the PSF in the reconstructed data cubes delivered by dither sequences that were not verified during commissioning, to measure the PSF at short wavelengths using a genuine point source rather than a slightly extended source, and to increase the SNR of the PSF and monitor any changes arising from changes in the configuration of the primary mirror. The activity will observe the bright star UMi, which is a point source at all wavelengths and will permit a proper measurement of the PSF in MRS Channels 1 and 2 , as well as the planetary nebula SMP LMC 058 using dither patterns not exercised during commissioning in order to ensure full characterization in Channels 3 and 4.
Program 1525 - CAL-MIRI-025 - MRS Dispersion Correction
This activity will measure the wavelength solution for the MRS by observing a Be star, which have spectra full of hydrogen recombination lines. The Cycle 1 Cal observations build on observations during Commissioning and will be especially helpful at longer wavelengths, where the sensitivity of the MRS is substantially lower.
Program 1526 - CAL-MIRI-026 - MRS Astrometry
This activity will monitor the accuracy of the mapping of astrometric position in the sky to x,y pixel coordinates on the two MRS detectors. It will observe a region within the JWST astrometric field with the MRS, MIRI imager, and FGS simultaneously with the goal of measuring the location of the MRS field in V2,V3 space, the distortion across the MRS field of view, and the same quantities in the MIRI imaging field. Distortion in the MRS is particularly important to monitor throughout the mission; the relative positions of the field of views are not expected to change substantially after commissioning, and this activity will demonstrate that near the end of Cycle 1.
Program 1527 - CAL-MIRI-027 - MRS Dynamic Range Characterization
This activity will monitor the MIRI MRS response to a standard star from the list of absolute flux calibration stars and characterize the MRS responsivity at very low flux densities. The objective is to investigate the noise properties of the MRS while observing faint targets and ensure that the spectral response remains valid. The target is the star P330E (G0 V, K=11.379), which will be observed once in Cycle 1 and once per year in the following years. The apparent noise in the spectrum and flux density of the star will be measured as a function of wavelength and compared to the predicted values.
Program 1528 - CAL-MIRI-032 - LRS External Flatfield
External flat fields will be taken to provide full flatfields for the MIRI LRS. These flats combine the information obtained separately as P-flats and L-flats for the imager. We will utilize the method tested during commissioning in CAR-MIRI-055 which steps a point source along the slit and across the SLITLESS subarray to build a flatfield. As in commissioning, we will use 1-pixel steps in the slit (45 pointings), but for slitless mode, we will use 2-pixel increments and cover the central 52 pixels of the slitless aperture (26 pointings; compared to a width of 68 science pixels), a change from Commissioning.
Program 1529 - CAL-MIRI-034 - LRS PSF Characterization
In order to characterize the point spread function (PSF) as a function of wavelength in the LRS slit and slitless modes, we will scan a point source across the two nod positions and the center of the slit and across the nominal pointing position in the SLITLESSPRISM subarray. These observations will improve the signal/noise ratio (SNR) obtained during commissioning in CAR-MIRI-074. Detailed knowledge of the LRS PSF and the availability of a super-resolution PSF model will test the WebbPSF model, improve the SNR of the outer PSF, and facilitate better algorithms for extracting spectra from two-dimensional spectral images.
Program 1530 - CAL-MIRI-035 - LRS Dispersion Correction
This activity will measure the dispersion solution for the LRS (slit and slitless) by observing Be stars, which have spectra full of hydrogen recombination lines. The Cycle 1 Cal observations build on observations during Commissioning and will be especially helpful at longer wavelengths where the sensitivity of the LRS is limited.
Program 1531 - CAL-MIRI-036 - LRS Slit Throughput
This activity will improve our understanding of the MIRI LRS slit throughput as a function of wavelength and position in the slit by scanning a point source across the slit at the two nominal nod positions. These scans will be longer than similar observations executed in Commissioning, will check the point-spread function (PSF) far from its center, and improve our calibration for extended sources. The scans will also confirm r the center of the slit, because the throughput from the target should be at a maximum when the telescope reports that it is pointing at the center of the slit in each scan.
Program 1532 - CAL-MIRI-042 - Coronagraph External Flatfield
This activity will build on commissioning activity CAR-MIRI-056, by providing updated flatfields for each coronagraphic aperture in Cycle 1. Both activities will provide data for two components of the flatfield: the Pixel-flat (P-flat) and the Low frequency flat (L-flat). The P-flat is obtained by dithering an extended source around each coronagraphic aperture, while the L-flat utilizes the 1000-points-of-light algorithm by dithering around a crowded star field. We will use the same technique as in commissioning: observing fields with strong zodiacal emission for the P-flats and the LMC astrometric field for the L-flats.
Program 1533 - CAL-MIRI-113 - Imaging Subarray Calibration
To provide the data necessary to transfer the photometric calibration of the MIRI imager across all subarrays, we will observe an A dwarf in the F770W filter in each subarray. The target is J1812095, which is in the continuous viewing zone.