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Last Updated  Sep 06, 2017

Some types of observations submitted in response to the DD ERS Call may require special accommodations for full specification in the Astronomers Proposal Tool.

The Astronomer's Proposal Tool (APT) is still under development. Consequently, there are known limitations for a number of observing modes that we describe in this section. At this relatively early stage of preparation for Cycle 1, other features or limitations may be discovered in the process of preparing DD ERS proposals. When necessary, major updates will be made to this document and included in the Late-Breaking News section of this call. However, it is expected that most updates to planning guides, or more specific submission tips, will be posted as articles in the JWST Help Desk, particularly in the Knowledge Base

General Considerations

Proposers should be aware that  there may be inaccuracies in the total charged duration reported in their APT submission. Known issues, such as uncertainties in the slew times for closely spaced observations, will be flagged in APT User Documentation; proposers should check that site for updates, as well as the Late Breaking News section of the Call.  In some cases, specific guidelines will be given with regard to adjusting the charged duration reported by APT; in those cases, the proposer should report and justify their corrected charged duration in the PDF of the proposal.

Proposers should be aware that accepted proposals may require modifications based on the results of the JWST commissioning process.

Mosaic Observations

Proposers are required to submit complete APT files of programs requesting mosaics by the proposal deadline, as this is the only way to estimate the total time requested. In addition, another reason for requesting complete APT files is because complex programs like large mosaics, that involve timing constraints, impose significant restrictions on the Long Range Plan and therefore need to be incorporated into the schedule as early as possible, in order to be able to accelerate the intellectual cycle. Proposers should be aware that:

1. The Guide Star Catalog used by APT at the time of the release of this Call (May 19, 2017) may be insufficient to find guide stars for all the mosaic tiles at the same time. In those cases, when running the program through the Visit Planner in APT, errors are triggered and the mosaic tiles cannot be scheduled simultaneously. If guide stars are not available for all the tiles at the same orientation, proposers should refer to the mosaic documentation for guidelines on how to proceed (see for example documentation discussing mosaic planning and tile splitting). Please note that it is important to resolve these scheduling errors before submission because otherwise smart accounting will not work and APT will assume each tile is a separate observation, each requiring a major slew, greatly overestimating the requested time.

2.  If  tile splitting is required for scheduling purposes, proposers are recommended to set the Position Angle at a value that allow the largest number of tiles to be scheduled simultaneously. Proposers should be aware that a fixed position angle imposes constraints on scheduling observations in the Long Range Plan. Consequently, if the proposal is accepted, STScI may adjust the Position Angle of the mosaic to minimize disruptions to the schedule. If a specific Position Angle is necessary to achieve the science objectives, this should be clearly indicated in the PDF of the proposal. Proposers are discouraged to request this unless necessary to achieve science objectives.

3.  Proposers should bear in mind that if tile splitting is necessary, observations of problematic tiles will be made at a different Position Angle from the majority of the mosaic. This may create gaps in the coverage. If the science goals require full coverage, the proposer should indicate this clearly in the PDF of the proposal because it may require adjusting the size and/or dithering pattern of the tiles that need to be scheduled separately.

NIRSpec MOS Observations

The target selection process for NIRSpec MOS observations must take account of how objects are projected onto the micro-shutter array, and therefore depends on the orientation of the observations and the distortions present along the NIRSpec optical path.   In general, to ensure program schedulability, NIRSpec MOS science observations should be submitted with no orient constraint in proposals. We recommend that proposers who wish to constrain their observation orient define a preferred orientation within a range of no less than 30o (or ±15o), with an appropriate scientific justification. The exact execution orientation for any observation will not be determined until that observation is placed on the Long Range Plan (LRP) for Cycle 1.  As a result, NIRSpec MOS observations cannot be fully specified at the time of submission. Proposers must submit in their proposals an associated source list for the final target assignment within any given pointing (see JWST DD ERS Special Observational Policies). Once the orientation has been defined for successful proposals, the proposer will be informed and can select the individual targets for MOS observation. A full description of the NIRSpec MOS APT submission process is given in the NIRSpec MOS JDox pages.

DD ERS proposers may not apply for NIRSpec MOS programs that require NIRCam pre-imaging to identify targets. Planning for NIRSpec MOS science must be based on catalogs and source information available at the start of Cycle 1.

Coronagraphic Observations 

Proposers are required to submit complete APT files by the proposal deadline as a means of specifying the total time requested and to identify available roll angles. However, proposers should be aware that:

  1. The PSF calibrator star that needs to be fully specified in their DD ERS proposals might be changed prior to executing an accepted program if both the proposer and STScI agree that this change is beneficial to the science yield of the program, under the condition that the science goals are unaffected and requested time is not increased.
  2. The overheads associated with a given observation depend on the exact observing sequence and the ordering of the exposures. Proposer should make their best effort to optimize the program by minimizing overheads following the guidelines in the High Contrast Imaging documentation. If the proposal is accepted, the Contact Scientist may also suggest changes to achieve this goal. 

Moving Target Observations

For a set of fixed target observations, after running the visit plannerSmart Accounting corrects the initial APT overhead estimate by considering that there is only one 1800 sec major slew on the first observation, while the rest of the observations have far smaller minor slew times (similar to slew times between visits within an observation). However, at the time the ERS call is released, Smart Accounting may not have been implemented for solar system observations. If this is the case, APT will overestimate overheads in moving target observations because it will assume multiple major slews when in reality the telescope will not need that much time to get to the target because it will be approximately there from the previous observation. Guidelines for manually correcting the slew time are given in Question #1 in this Knowledge Article on solar system targets. The corrected time would need to be introduced in APT by clicking on the "Request custom time allocation" under the Charged Time, entering a TIME REQ EXPLANATION of "Manual accounting correction for Solar System target". In addition, in the PDF attachment of the proposal, proposers should include an explanation of how they calculated their own estimate of the time, taking into account the need for only one major slew, when appropriate. If by the time of the final APT submission, after the proposal has been already approved, Smart Accounting were to be implemented for moving targets, the APT-calculated time estimates would be adopted. 


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