Webb Proposing Support Tools
Bill Blair, email@example.com
All users of Webb will need to craft proposals that describe their desired observations in sufficient detail to permit the ultimate scheduling of the observations once the proposals are accepted. Users of Hubble will be familiar with the Astronomer's Proposal Tool (APT), which supports users performing this task. A branch of APT to support Webb observers is well along in development and is available1 for potential proposers to become familiar with it. In addition to APT (described below), there are other tools that are being developed that are useful to proposers prior to using APT, to assist them in preparing their observing requests. Here is a brief outline of the tools we expect to provide before the release of the first call for proposals in 2017.
Webb Exposure Time Calculator (ETC)—The ETC models the observatory and a specific instrument package by constructing full three-dimensional astronomical scenes and "observes" them with a model instrument, producing two-dimensional detector-plane products and methods for extracting signals, such as spectra or photometry. The ETC will allow a user to experiment with various instrument configurations in order to assess whether they are feasible, and then estimate how much exposure time will be required to complete the requested observations (see Figure 1). Each proposer will create a private workbook that will contain their set of calculations for a variety of instruments or configurations and will be able to share their workbook with Co-Is, establishing a collaborative environment for pre-proposal work. Final calculations will form the basis for the information that will be transferred to APT to specify requested observations and target acquisitions. The full Webb ETC application will be released in January 2017.
Webb Target Visibility Tool—The entire sky is available to Webb observations, but not all at the same time. APT will provide a detailed assessment of the schedulability of proposed observations, but many users will find it to be a significant time savings to understand the observability of a target prior to entering their proposal into APT. Any targets needing observation at a particular time, time separation, aperture position angle on the sky, or aperture position angle offset between observations may have significantly constrained visibility or even be unschedulable. A basic target visibility tool will allow the user to perform a quick assessment of target visibility. A more sophisticated GUI-based version will be available to support coronagraphic proposers who may have specific concerns about the placement of companion planets and/or orientation of disks relative to instrumental features (see Figure 2).
WebbPSF—This tool is already available2 and allows users to calculate and examine the Webb Point Spread Function (PSF) for a range of assumptions. This tool may be particularly useful for coronagraphic proposers, or for any other situation where the PSF characteristics could affect the science. The engine behind the WebbPSF tool also is used within the Webb ETC when generating scenes.
Duplication Checking—Users will be required to identify and justify any proposed observations that are duplications or potential duplications with previous observations (and/or accepted and planned observations). Many users may want to perform this check prior to crafting their proposals. To enable this, prior and planned observations will be provided to the Mikulski Archive for Space Telescopes (MAST) in a form that even Cycle 1 proposers will be able to check against Guaranteed Time Observer and/or Director's Discretionary–Early Release Science planned observations. In addition, we anticipate that a tool within APT itself will provide the user with connectivity to MAST to check their final proposal for duplications prior to submission.
Astronomer's Proposal Tool (APT)—This is the parent tool that will be used to prepare and submit all proposals, providing the detailed information for observation requests. It is the goal of the Webb APT to enable a single-stream submission process by making it straightforward for users to enter complete or nearly complete observing specifications for most proposals at the time of the initial submission. The Webb APT has a number of aspects that are specific to Webb as well as some aspects that will look familiar to Hubble users. In reality, APT is a suite of tools that get used together to formulate, check, and ultimately submit proposals.
To enable the single-stream proposal approach (discussed in the article by Amaya Moro-Martin in this same issue of the Newsletter), the Webb APT has been developed with a concept called observation templates. Spitzer users will be familiar with this concept. After the user chooses an instrument (say MIRI) and specifies a particular "template" or observing mode (say Imaging), the GUI changes to show the user only those elements the user needs to be concerned with for that template (see Figure 3). Pull-down menus show the available options for such things as filters, gratings, or options for dithering, and tabs are provided for options such as Special Requirements or Mosaic specification (as appropriate for a given template).
For Webb APT, it is important to understand some basic terminology and concepts that are used differently from the Hubble version. Users specify observations of targets, using observation templates. Based on the inputs from the user, APT decides whether the observation needs to be broken into multiple pieces called visits, and each visit may involve one or more exposures on a target, which is controlled by the observation specification provided by the user. It is important to understand that visits are the scheduling units used by the downstream scheduling system, but observations are what the user specifies in APT.
After observations are specified in APT, the user can select one or more observations and activate the Visit Planner (VP) aspect of APT. The VP looks at the actual schedulability of the potential observation, including not only the visibility to the observatory over time but also whether guide stars are available versus time. Any errors found by the VP need to be resolved prior to submission3 and various diagnostic plots and other information is available to the user (see Figure 4). Because APT handles so many of the scheduling complications behind the scenes, the APT software applies various rules and assumptions for calculating the appropriate overheads and ultimately producing a total resource estimate for the proposal. Once the entire set of observations has been specified and run through the VP, a final accounting is done to remove unnecessary or redundant preliminary overheads and return a final resource estimate for the proposal. This resource estimate is binding and is reported to the TAC panels as part of the proposal assessment process.
Multi-Object Spectrograph Planning Tool (MPT)—This tool, integrated into APT, will allow users to plan NIRSpec Multi-Object Spectrograph observations using the Micro-Shutter Array (MSA). This is likely the most complex planning process for Webb. Proposals without existing target catalogs of sufficient astrometric accuracy will only be able to craft provisional programs (requesting the number of MSA configurations and exposure times) until they obtain pre-imaging catalogs from (for instance) NIRCam pre-imaging. The MPT is then used again to produce the specific set of observations to support the proposed science program.
Aladin Visualization Tool—This tool, integrated into APT, allows users to see their proposed observations in context by projecting the relevant instrument fields of view onto the sky. Examples include verifying that the dither pattern specified in an observation really produces the desired effect, checking a proposed mosaic observation for its coverage of an extended source, or seeing the effect of various fixed position angles of a given instrument or field of view. Users are encouraged to experiment with this tool prior to detailed proposal planning.
APT help will be available in the form of documentation, use case examples, demonstration videos, and contextual help from within APT itself.
With a new observatory, new instruments, and new software, it will be important for everyone interested in proposing for Webb to invest the time and effort necessary to understand and use the proposing support tools. Scientists and developers at the Institute are working closely together to get these tools and the accompanying documentation in place to support the user community. Some of these tools are available in preliminary form already, while others will come online in the coming months. Stay tuned to future Newsletters for details on how and when you can access the various tools to begin the process of familiarizing yourself with them. The article by Christine Chen, in this same issue of the Newsletter, describes the different opportunities the Institute will be offering the community in terms of training on these proposal preparation tools.
1 Users can access the Webb portion of the tool simply by downloading and installing the current version of APT. Open the APT GUI and select "New JWST proposal" from the "New Document" pull-down menu. The APT flight build for Webb (supporting the GO Cycle 1 call for proposals) will be released in the spring of 2017. See the article by Neil Reid, in this same issue of the Newsletter, for more information on the timeline of APT releases and calls for proposals.
3 Proposals flagged with warnings by APT, rather than errors, will be allowed to be submitted.