JWST High Contrast Imaging Roadmap

This roadmap outlines the suggested flow of planning considerations required for a High-contrast Imaging (HCI) observation with JWST and should be used in consultation with the General Proposal Planning Workflow.

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Introduction

High-Contrast Imaging (HCI) observations can be some of the most complex to schedule with JWST and for that reason the workflow of this roadmap is considered iterative. When planning HCI observations many parameters come into play and for some science cases, it is not always initially apparent which HCI mode—if at all—will provide you with the best scientific results; users may find themselves returning to earlier steps before "linearly" producing their proposal and APT files.


Stage 1: Becoming familiar with the HCI capabilities and instrument-specific modes of JWST

In extension to the steps suggested in the General Proposal Planning Workflow ("Become familiar with JWST capabilities and terminology"), users should consider the following in particular to High Contrast Imaging: 


  1. Which of the JWST observing modes enable HCI?

    MIRI Coronagraphic Imaging between 10 and 23 µm.

    NIRCam Coronagraphic Imaging between 1.8 and 5 µm.

    NIRISS Aperture Masking Interferometry enabling high spatial resolution, moderate-contrast imaging between 2.7 and 4.8 µm.

    Imaging & IFU Spectroscopy with non-coronagraphic PSF subtraction strategies enabling moderate-contrast imaging[1].

  2. What HCI optical designs are offered by JWST?

    You should familiarize yourself with the advantages, limitations and functionality of each particular HCI design, as well as which scientific investigations they are optimized for.

    JWST High-Contrast Imaging Optics:

    Lyot-type Coronagraph: five implementations in NIRCam, one in MIRI.
    Four-quadrant phase-mask coronagraph (4QPMC): three implementations in MIRI.
    Non-redundant mask (NRM): one implementation in NIRISS.

  3. What are the allowed mask-filter combinations for each of the HCI modes?

    MIRI: focal plane coronagraph masks

    (3x 4QPMs, 1x Lyot spoteach of which images to a different pupil mask and coronagraphic filter combination.

    NIRCam: sets of 5x occulting masks

    (3x round, 2 bar-shaped) usable with a subset of permitted filters depending on the selection of mask.

    NIRISS: a 7 hexagonal hole 

    (generating 21 baselines) Non-Redundant Mask in the pupil plane usable with 4 NIRISS filters to enable AMI mode.

  4. What are the primary performance metrics for HCI?

  5. What are the predicted performances[2] of the instrument-specific modes?

    MIRI: achievable IWAs of 0.34–2.19′′

    (1 λ/D for 4QPMs, 3 λ/D for Lyotand typical contrasts[2] achieve 10-4 to 10-5 for separations larger than 0.5″–1″.

    NIRCam: achievable IWAs of 0.14–0.89" 

    (round and bar-shaped occulters optimized for 6 λ/D and 4 λ/D, respectively) and contrasts typically ∼10−6 or better at 1′′ IWA and beyond.

    NIRISS AMI: achievable IWAs of 0.089–0.15"

     (1 λ/D) and contrasts typical contrasts ~10-4 at separations of ~70–400 mas.

    Imaging and IFU Spectroscopy:

    (with non-coronagraphic PSF subtraction) achievable contrasts ~ 10-3 to 10-4 and IWAs somewhere between those of AMI and Coronagraphy for a given filter.

  6. What are the fundamental physical limits for detection?

    Photon Noise of the stellar Point Spread Function (PSF):

    MIRI Point Spread Functions
    NIRCam Point Spread Functions
    NIRISS Point Spread Functions

    Detector noise:

    MIRI Detector Performance
    NIRCam Detector Performance
    NIRISS Detector Performance

    Background Noise (zodiacal light + thermal emission) esp. longward of ~15 μm.

  7. What are the operations unique to HCI?

  8. What are the recommended observing strategies pertaining to HCI?


Stage 2 — Comparing your parameter space to the performance limits and capabilities of the HCI observing modes.


  1. Identify the wavelength range(s) of interest for your intended science. How does this influence (or limit) your choice of science instrument(s), mask(s) and filter(s)?

    MIRI coronagraphic imaging:  

    3x 4QPMs operating with narrow-band filters centered at 10.65, 11.4, and 15.5 μm and 1x Lyot coronagraph working in a broad-band filter centered at 23 μm.

    NIRCam coronagraphic imaging:  

     1x extra-wide, 4x wide-, 10x medium- and 2x narrow-band filters (depending on the selection of coronagraphic mask), in the wavelength range 1.82–5.0 µm. 

    NIRISS AMI:

     in order to enable AMI modethe NRM will be used in conjunction with one of the 3x medium-band filters centered at 3.8 and 4.5 μm or a wide-band filter centered at 4.8 μm.

  2. Determine the apparent separations, between your host and companion source(s) at the time of observation. Which instrument(s) and mask-filter combination(s) can achieve the required working angles?

  3. Determine the companion contrast(s) at the wavelength(s) of interest. Are your observations feasible given the contrast limits of the instrument(s)?

    Note: when referring to a companion, the term "contrast" corresponds to the ratio of the companion's observed flux to that of its host. An observation is estimated to be feasible if the companion-to-host flux ratio is greater than the "limiting contrast" Climit(s).

    Modeling may be required to extrapolate out shorter wavelength measurements to 3 – 23 μm regime for these predictions (e.g. to determine companion contrasts at MIRI wavelengths from far infrared or submillimeter data). 

    Contrast Considerations for JWST HCI

    MIRI-Specific Treatment of Limiting Contrast
    NIRCam-Specific Treatment of Limiting Contrast
    NIRISS AMI-Specific Treatment of Limiting Contrast

  4. For coronagraphic observations, how important is the azimuthal coverage around your science target? 

    MIRI coronagraphic imaging

    with the 4QPMs, the linear boundaries between adjacent quadrants attenuate light, reducing sensitivity in the field along the four edges of the mask.
    with the
     Lyot coronagraphthe Lyot spot is suspended in the focal plane by two supporting struts in the mounting bracket, which themselves block light in the FOV.

    NIRCam coronagraphic imaging

    the round occulting masks provide 360azimuthal coverage around the bright object.
    the 
    bar occulting masks sacrifice some FOV in the direction along the bar, as a function of azimuth around the bright object.

  5. Is it possible that your scientific goals can be achieved with non-coronagraphic PSF subtraction? 

     For moderate contrasts (~ 10–3 to 10–4) and/or point source detections well in the background limited regime, it might be wise to opt for one of the standard imaging modes.

    JWST Imaging


Stage 3 — Selecting a PSF calibration strategy

All HCI observations with JWST require the measurement and calibration of stellar point spread functions (PSFs) in some way for post-processing contrast reduction. For any PSF calibration strategy, the observing and data processing techniques are interdependent.

Skip to Interferometry Calibration Strategies


Coronagraphic PSF subtraction strategies

In order to achieve the necessary high-contrast and recover faint sources surrounding the science target, one must calibrate and subtract out the PSF of the central source.

  1. Consider the degrading factors that may limit the PSF calibration and what steps you will take to mitigate them. 

    These include wavefront drifts of the observatory, PSF star color differences, self-subtraction biases (especially for disks), imperfect target acquisitions, line-of-sight jitter and dynamic wavefront error.
    JWST Wavefront Sensing and Control
    PSF Subtraction: the effect of spectral "mismatch"

  2. Which observing technique(s) will you include in your PSF subtraction strategy?

    Each PSF calibration and subtraction method has a corresponding observing strategy. The imaging techniques are combined with post-processing optimization algorithms (such as LOCI[4] and KLIP[5]) to generate an optimal synthetic reference PSF, to be subtracted from the science target image. 

    Will you employ the Referenced Differential Imaging (RDI) technique? — Required

    In this techniquethe observation of a nearby star is used to generate an unresolved, high signal-to-noise (SNR) PSF to subtract from the science target.
    (minus) The RDI technique is sensitive to wavefront drifts and PSF star color differences.

    By scheduling the Science and PSF reference observations back-to-back in a sequence, the effect of wavefront drifts should be minimized.

    Will you employ the Angular Differential Imaging (ADI) technique? — Recommended

    In this technique, the science target is observed at two different roll angles and is used as a self-reference for PSF subtraction. 
    (plus)  ADI allows for PSF subtraction at nearly the same spacecraft attitude (for wavefront stability) and helps mitigate detector artifacts.
    (minus)  However ADI comes at the cost of self-subtraction biases, especially given the limited available roll (~10deg) of JWST.

    For robustness, it is strongly recommended to obtain observations using both RDI and ADI PSF calibration techniques. You can deviate from this plan if desired, but most explain your alternate PSF subtraction strategy in your proposal.

    See the Standard Coronagraphic Sequence.

    Will you employ the Small Grid Dithering (SGD) technique? — Optional

    This technique involves performing sub-pixel dithers of the PSF reference target, to build a mini library of reference images that effectively samples the PSF diversity close to the center of the coronagraphic mask.

    (plus) The SGD technique can be used to mitigate possible misalignments between science and reference images, reducing the contrast loss from TA (pointing offset) residuals to a negligible level (10x contrast improvement for MIRI, 3-5x improvement for NIRCam)
    (minus) However, SGDs 
    come at the cost of (5-9x) longer PSF star exposure times. 

    The SGD technique is optional, and should only be used when the highest quality PSF subtraction is needed.

    JWST Small Grid Dither Technique
    NIRCam Small Grid Dithers
    JWST Coronagraphic Sequences: Use of the small grid dithering technique

    Non-coronagraphic PSF subtraction

    Using the same PSF subtraction methods, it is also possible to achieve high performance with non-coronagraphic imaging modes, such as direct imaging in filters that may not have coronagraphs available, or using one of JWST’s integral field spectrographs in NIRSpec or MIRI. The contrasts achieved with such modes, even with careful PSF calibration, will not equal the contrasts achieved with the coronagraphs—but even “moderate” contrasts can still offer compelling science capabilities. Such observations are already planned for Cycle 1 by both GTO and ERS teams.



Interferometry Calibration Strategies 

For NIRISS AMI, the observations of calibrator stars are used to measure, then remove, instrument systematics. The PSF (or interferogram) produced by the NRM has a narrow central core which is surrounded by an extended skirt created by interference between pairs of apertures. These fringes in the outskirts of the NRM PSF are easily measurable due to their relative brightness and wider angular extent, making instrumental effects easier to calibrate out of science data.

  1. Which observing technique(s) will you include in your PSF calibration strategy?

    Will you observe a PSF reference calibrator?

    The observation of a calibrator star allows for the instrumental systematics (affecting interferometric observables) to be measured. The reference PSF is used to calibrate out the instrumental contributions to closure phases (CP; the sum of three phases around a closed triangle of baselines) and squared visibility amplitudes (SqV), during the 3rd stage in the calibration pipeline (CALWEBB_AMI3).

    Near-contemporaneous acquisition of target and point source calibrator data is desirable, except for very low contrast needs: if contrast limits are not very demanding, a reference star from an unrelated observation, or possibly an analytically generated reference PSF can be used.

    AMI-specific treatment of limiting contrast
    NIRISS AMI Recommended Strategies

    Will you employ the Kernel phase imaging technique?

    In this technique, one or more direct images using the CLEARP aperture and the same suite of FW filters as those used for the NRM images are obtained for PSF characterization.




Stage 4 — Assessing target visibilities and allowed position angles 

The following steps should be used in conjunction with those outlined in the General Proposal Planning Workflow ("Determine if your targets can be observed")..

  1. Familiarize yourself with JWST position angles, coordinate systems, and related nomenclature to understand the telescope’s pointing constraints. 

  2. Determine the viewing constraints are placed on your target(s).

  3. Using at least one of the JWST target visibility tools, assess your target visibilities and allowed position angles versus time.

  4. In the case of known companions, consider whether your observations require any restrictions on the orientation of the instrument field of view (FOV)/ detector being referenced.

    Especially in relation to any instrumental obstructions, such as cross pattern for the MIRI FQPM, bars for NIRCam, or outside of gaps in the uv-pane coverage for NIRISS.
    Using the CVT: Adding companions to the primary target

  5. If implementing the ADI technique in your PSF calibration strategy (Stage 3):
    Check how the instantaneous roll flexibility changes over the the particular visibility period.

    This instantaneous roll flexibility is approximately ±5° from nominal, but varies with time and look direction between ±3.5° to ±7°.
    JWST Target Viewing Constraints

  6. In the case of coronagraphy, consider whether your goals call for a larger roll offset on the science target than can be obtained instantaneously in a single visibility period.

    Certain science cases may require a follow-up at some more substantial angular offset (e.g. 30° offset) relative to the first observations—for instance, to recover part of the scene that may be blocked by the selected mask. In such cases, the observation will have to be scheduled at a significantly later time. 
    Coronagraphic observers will want to assess their potential targets carefully, and when possible, select targets above 45° ecliptic latitude if they require large offsets in PA between observations.

    The effect of a target's ecliptic latitude

    The Coronagraphic Visibility Tool (CVT) can be used to assess the availability of multiple position angles, and estimate what the time separation will be. It is expected that each sequence will contain an observation of a relevant PSF reference star, since the PSF will likely change between the two epochs.


Stage 5 — Use the ETC to determine your observing parameters

Once target visibility is confirmed and a PSF calibration strategy adopted, the JWST Exposure Time Calculator (ETC) should be used to determine the exposure parameters needed to achieve the desired signal-to-noise (SNR) on your target(s). Aside from the directions in the General Proposal Planning Workflow, the following are advisable for HCI:

  1. Define your Scenes and Sources. 

    Create a Science Scene and populate it with the source targets

    The Science scene should contain the source targets for observation and all other nearby sources that could contribute to both the observed target and background fluxesThe bright ("host") source should be placed in the center of the scene and the reference PSF source(s) at a significant Offset (e.g. 10 arcsec).

    At this stage, a copy of the bright target can be used as a proxy for the reference PSF source—that is, until a physical PSF calibrator has been identified in STAGE 6

    Faint sources must be placed within a square centered on the scene center for each instrument/mode pairing.
    → for MIRI the scene is a 8.91" square centered on the coronagraphic masks.
    → for NIRCam the scene is a 6.36" square centered on the coronagraphic masks.
    → for NIRISS the scene is a 5.31" square centered on the NRM.

    Create a Reference Scene and populate it with the reference PSF source.

    In order to facilitate Target Acquisition calculations for the reference PSF source, a dedicated "Reference" scene—containing only the reference PSF target—is required. The reference PSF source should be positioned at the center of the scene (offset 0,0).

  2. Initiate calculations for each of your planned observations.

    Calculations are performed from the Calculations page where the user specifies the desired input parameters in the Configuration pane(1) instrument and mode, (2) scene, (3) background model parameters, (4) instrument configuration, (5) detector setup, and (6) the strategy for calculation of the SNR (and contrast for coronagraphic modes). 

    JWST ETC Creating a New Calculation
    JWST Coronagraphy in ETC
    JWST ETC Coronagraphy Strategy
    JWST ETC Imaging Aperture Photometry Strategy

  3. Adjust the exposure time via the NUMBER OF GROUPSINTEGRATIONS, and/or EXPOSURES until you obtain the desired SNR and contrast on your target.

    Understanding Exposure Times
    MIRI Generic Recommended Strategies: How many groups and integrations should I use?
    NIRISS AMI Recommended Strategies: Estimating number of groups for an exposure

    While the web-based ETC is perfectly adapted and trustworthy for the SNR calculations occurring in the background limited regime, in the speckle-limited regime (typically from the IWA to 1 to 2"), the Pandeia-Coronagraphyenter image description here extension of the ETC's Pandeia engine is recommended for more realistic contrast and detection limit calculations. The Python-based package also provides capability to introduce mis-registration of the PSF reference star and to experiment with small-grid dithers.

    For NIRISS AMI, there is an advanced Python tool and precomputed contrast curves found at https://github.com/agreenbaum/ami_simenter image description here and hbp://maestria.astro.umontreal.ca/niriss/AMIcontrast/index.phpenter image description hererespectively.


  4. Check your individual calculations for detector saturation.

    The user checks for saturation using the Saturation tab in the Images pane on the Calculations page in the ETC.

    While some saturation may be tolerable, only partially-saturated pixels will be recoverable. In saturated regions, the photometric accuracy will be sub-optimal and the contrast will most likely be affected at or close to the IWA; consequently, faint portions of the astronomical scene that overlap with saturated pixels may not be properly detected. 
    JWST ETC ReportsJWST ETC Calculations Page OverviewJWST Coronagraphy in ETC: avoiding saturation

    Using the Saturation Map, check if any saturated pixels overlap with faint sources/features in the astronomical scene.

    In the event of saturation, it may be possible to recover pixels at the expected position of the companion by modifying the exposure parameters: proceeding by trial and error, vary the readout pattern, Ngroups and/or Nints until all pixels at the expected position of the companion are no longer saturated.
    JWST ETC Images and Plots

  5. Initialize Target Acquisition (TA) calculations for each of your observations.

    All HCI observations will require a science instrument assisted TA procedure—this includes both science and reference PSF observations.
    JWST ETC MIRI Target Acquisition
    JWST ETC NIRCam Target Acquisition
    JWST ETC NIRISS Target Acquisition

  6. Run your TA calculations and examine the output information.

    JWST ETC Outputs Overview

    1. Does any saturation occur?

      Saturation should be avoided during target acquisition for optimal performance. If any fully or partially saturated pixels are present in the TA exposure, the ETC will issue a warning. The recommendation is to adjust your exposure parameters (e.g., by decreasing the number of groups) to avoid saturation.
      MIRI Outputs for TA
      NIRCam Saturation limits for TA
      NIRISS Outputs for TA

    2. Does your exposure specification allow you to obtain the minimum required SNR for the TA procedure of the instrument mode?

      MIRI Coronagraphic Imaging TA

      requires a SNR ≥ 20 to obtain an absolute centroid accuracy of ≤ 10 and 22.5 mas for the 4QPM and Lyot coronagraphs, respectively.

      NIRCam Coronagraphic Imaging TA 

      requires a SNR ≥ 30 to obtain a centroid accuracy ≤ 0.1 pixels for the TA source.

      NIRISS TA

      requires a SNR ≥ 30 to achieve a centroiding accuracy of ≤ 0.15 pixel for the TA source.



Stage 6 — Selecting a suitable PSF calibrator

If you have established the need for a PSF reference target according to your PSF calibration strategy designed in STAGE 3, this section is relevant. Otherwise, continue to STAGE 7.

  1. Select a PSF reference calibrator with consideration of the following criteria:

    1. Well-known: Is the target a known good PSF reference star? 

      Selecting a reference PSF source that has been perviously observed interferometrically/ coronagraphically and found to be single, is recommended. "Good references" are usually stars that are not astrophysically contaminated (i.e., without additional astrophysical signal from a debris disk or companion). 
      MIRI Coronagraphic Recommended Strategies: choosing a reference PSFs target
      NIRCam Coronagraphic Recommended Strategies: Selection of PSF Reference star
      NIRISS AMI Recommended Strategies: Choosing an optimal calibrator for NIRISS AMI

      There exist a handful of external resources that can helpful in the search for a known PSF reference target. See Selecting PSF reference stars with Simbad and Selecting PSF reference stars with SearchCal for more information.  

    2. Schedulability: Do the visibility windows of the science target and PSF calibrator overlap at the time of the desired observation?

      Science and PSF reference observations should be executed as close together in time as possible in order to minimize changes in the PSF and obtain the lowest possible limiting contrast.
      Checking visibility of PSF reference stars 
      Coronagraphic Visibility Windows
      JWST Wavefront Sensing and Control

    3. Proximity: Is the PSF calibrator in relative proximity to the science target? 

      In order to limit thermal changes and minimize telescope overheads. 
      Selecting Suitable PSF Reference Stars for JWST High-Contrast Imaging
      Slew Times and Overheads

    4. Avoidance of Binary: Is the PSF calibrator a single and unresolved source?

      This can be addressed by selecting a known good PSF reference star.
      Selecting Suitable PSF Reference Stars for JWST High-Contrast Imaging

    5. Spectral Type: Does the PSF calibrator the share the same spectral properties as the science target? 

      This has a stronger impact at shorter wavelengths and with wider filters. Spectral mismatch may generate extra noise during the process of photometrically rescaling the reference and allow possible under- and over-subtraction of the PSF.  
      Effect of spectral "mismatch"
      High-Contrast Imaging Inner Working Angle

    6. Brightness: Is the PSF calibrator similar in magnitude to the science target? 

      Whenever possible, it is recommended to use a reference PSF that is brighter than the science target because the process of flux rescaling also scales the noise. Selecting a calibrator that is as bright as (or brighter) will help achieve the same signal-to-noise ratio in comparable exposure times. 
      Effect of spectral "mismatch"

  2. Return to your previous workbook the ETC (created during STAGE 5) to amend the spectral properties of the reference PSF source and finalize the exposure parameters of your calculations.


Stage 7 – Decide on your observing strategy

In previous stages, you have made a series of choices concerning the content of your observing program—in this stage, you will decide on an observing strategy with which to structure this content. This observing strategy should be designed to mitigate performance degradation and yield the best possible scientific results, with the least possible overheads.
MIRI Observing Strategies
NIRCam Observing Strategies
NIRISS Observing Strategies

  1. Consider the total number of observations you will require for your observing program.

    Note that PSF Reference observations should be observed using the same telescope optical configuration, so that no wavefront correction should occur between any of the observations. 

    The inference of the above is that observations in different filters require individual PSF reference observations.

  2. At the observation level: consider how you will organize (group) your observations.

    Observations that need to be executed together in time should be grouped together in "sequences". Details of these sequences will depend on the science goals of your program. 

    Science and Reference PSF observations

    For all HCI modes, Science and PSF reference star observations must be grouped into sequences—the goal is to minimize changes in the optics that might alter the PSF between observations. 
    JWST Coronagraphic Sequences

    NIRISS AMI Recommended Strategies: Observing calibrator(s)


  3. If your sequence of observations involves the use of multiple filters and/or occulters, you should consider following the optimal efficiency scheduling strategy.

    With the optimal efficiency strategy, observations for a given target are organized—in each filter and occulter—to minimize the number of rolls and slews. This strategy increases the time between an observation of a target in a given filter and the corresponding reference PSF star observation in the same filter, but it results in more efficient use of the observatory. With the optimal wavefront stability strategy, standard sequences are executed consecutively in each filter to minimize the chance of any wavefront changes, which comes at the cost of increased number of slews and rolls for the telescope. 
    JWST Coronagraphic Sequences: Standard sequence implementation for multiple filters and occulters

    Linking too many observations together into a sequence can make the total execution time long, to the point that the observations cannot be scheduled. Therefore, you should seek to strike a balance between efficiency and the pragmatic aspects of scheduling observatory activities.

    You may find it instructive to inspect the reports that are generated by running Smart Accounting in APT. These files provide a more detailed breakdown of where various overheads are being charged and will help you understand the tradeoffs in efficiency for the different models. See the articles on the APT Visit Planner and APT Smart Accounting for more information.

  4. Do your observations call for a more substantial position angle offset (e.g., 30° offset) on the science target than can be provided instantaneously in a single visibility window?

    For instance: to recover a part of the scene that would otherwise be blocked by a selected mask. The possibility of such an offset depends strongly on the ecliptic latitude of the target and must be scheduled at a significantly later time. The CVT can be used to help assess this. This special requirements should only be used when truly necessary for the science.
    JWST Coronagraphic Sequences: Larger roll offset case


  5. If your program consists of a set of science targets that are clustered on the sky in close proximity and schedulable at the same time:

    is it possible implement the shared reference survey strategy?

    Whereby multiple science targets are paired with an individual PSF observation, in the normal coronagraphic sequence?
    JWST Coronagraphic Sequences: Shared reference survey case
    Coronagraphic Visibility Tool

    Is it possible to incorporate the self-referenced survey strategy?

    Under the assumption that some science targets will be for science, but others—those not showing surrounding structure—will be used for PSF reference observations? 
    JWST Coronagraphic Sequences: Self-referenced survey case

  6. For all coronagraphic imaging programs: it is highly recommended to perform the standard coronagraphic sequence, or a derivative of it.

  7. Do your science goals call for high accuracy astrometry? 

    If so, perhaps you should obtain NIRCam images for full field astrometry (FFA) in addition to your HCI science data?
    NIRCam Coronagraph Astrometric Confirmation Image



Stage 8 – Implementation into the Astronomer's Proposal Tool

Aside from the steps described in the General Proposal Planning Workflow roadmap, consider the following particular to HCI:

  1. Organize science and PSF calibrator observations into sequences (to be scheduled back-to-back). 

    You may find it useful to collect all observations that pertain to a particular coronagraphic sequence into a single Observation Folder, and additional folders for other sequences. 
    JWST Coronagraphic Sequences

  2. Use the PSF Reference Observations section to indicate which observations produce PSF references and to specify to which science observations they should be linked. The PSF reference star must be in the same FILTER and SUBARRAY.

    You may find it very helpful to use designations in the Name in the Proposal field (Fixed Targets form) to clearly indicate which targets are intended for science and which are PSF reference stars, as appropriate. These designations will show up in the pull-down menus in other parts of APT, to help you build up your observation sequences. Furthermore, if you have a large number of science targets and PSF stars to keep track of, you may find it useful to do so using the the comment box.

    JWST HCI in APT: Setting links between PSF reference and science observations
    MIRI Coronagraphic Imaging APT Template: PSF Reference Observations
    NIRCam Coronagraphic Imaging APT Template: PSF Reference Observations
    NIRISS AMI APT Template: PSF reference observations

  3. If excluding the observation of a PSF reference target justification must be reflected in the Additional Justifiction section.

  4. Are NIRCam full frame astrometric (FFA) images are needed? 

    If so, indicate Yes in the Astrometric Confirmation Image Parameters template panel and enter the appropriate exposure information for these images.
    NIRCam Coronagraphic Imaging APT template: Astrometric Confirmation Image Parameters

  5. For Coronagraphic Imaging modes: Do any of your observations require the small grid dithering (SGD) technique?

    This selection can be made in the observation template by choosing the appropriate Dither Type, in the MIRI template, or Dither Pattern in the NIRCam template.
    Specifying SGDs in APT

  6. Add any the necessary Special Requirements:

    Timing Special Requirements,
    Aperture Position Angle Special Requirements
    Video tools are available for: Adding Special Requirements in APT

    SEQUENCE OBSERVATIONS... NON-INTERRUPTIBLE to force the Visit Planner to look at the collective schedulability of the entire set.

    Note that APT will execute the observations in a Sequence Observations ... Non-interruptible grouping in the order of increasing observation number. If you drag and drop the order of your observations in the APT tree editor, make sure the desired sequence of observations is still in increasing order of observation number. If it is not, edit the observation numbers so that ordering is achieved.
    APT Visit Planner

    APERTURE PA OFFSET ... for roll-dithered science target observations.

    Set the offset angle, or offset angle range between two roll-dithered observations. If a second sequence at a larger PA offset is needed, the Aperture PA Offset ... special requirement must still be set between the two sequences. The cases needing this level of attention to detail should be checked out ahead of planning, with a visibility tool (STAGE 4).

    APERTURE PA RANGE ... fix the allowed degree range of absolute PA on an observation.

    This is only necessary if a known structure around a given target (say a disk or known planet) needs to be positioned as to avoid structures in the instrument field of view. 

    Users should only constrain the requested angles when necessary to support their science goals and that even when an angular constraint is placed, the larger the range that can be allowed the better (from the standpoint of allowing scheduling flexibility). As an exercise, the user can try editing the special requirement that sets the allowed range of angles on the first observation and re-run the Visit Planner to see how the allowed time window changes.

  7. Verify your observation set-up.

    i. The APT Aladin Viewer can be used to visualize the field of view on the sky for planned JWST observations.

    Verify that the position angle(s) and roll dither(s) of an observation/ visit have been specified as intended.
    JWST APT Aladin Viewer
    Video tutorials are available for: Aladin Overview in APT: part 1Aladin Overview in APT: part 2Using Aladin and APT Visit Planner Together

    ii. Run the APT visit planner.

    Check scheduability of observations, check constraints and see whether guide stars are available to support the observations. 
    APT Visit Planner
    Video tutorials are available for: Reviewing Errors and Warnings

    iii. Create Target Confirmation Charts.

     to verifyithat the input target coordinates will position the telescope in the correct place.
    APT Target Confirmation Charts

  8. Using the Smart Accounting Reports are you able to identify the trade-offs in efficiency (science time/total time) for different observation strategies? 

    Note: programs that minimize the number of major slews and the number of visits will typically achieve a higher efficiency than programs with large numbers of slews and visits.
    APT Smart AccountingJWST Slew Times and OverheadsJWST Observing Overheads Summary, JWST Instrument Overheads



Footnotes

HCI can be carried out using basic imaging modes of the observatory (Rajan et al., 2015enter image description hereDurcan, Janson, and Carson, 2016enter image description here), as well as using IFU strategies similar to Konopacky et al. (2013)enter image description here, however these modes are not yet covered in the documentation. 

2 Based on performance simulations and contrast predictions based on the latest information on the as-built telescope and instrument properties, including both static and dynamic contributions to wavefront error (see M. D. Perrin et al. 2018)

We report all contrasts as 5-σ post-processing contrasts after single reference star subtraction.

4 KL image projection (KLIP) algorithm (Soummer et al. 2012)

“locally optimized combination of images” or LOCI algorithm (Lafrenière et al. 2007)

4 Bold italics font style is used to indicate parameters, parameter values, and/or special requirements that are set in the APT GUI.

References

JWST technical documents

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