NIRSpec MSA Planning Tool, MPT
The MSA Planning Tool (MPT), in the Astronomers Proposal Tool (APT), is used for the preparation of NIRSpec multi-object spectroscopy observations.
This page introduces the MSA Planning Tool (MPT), which can be found within the JWST Astronomers Proposal Tool Overview (APT). Here, we provide a basic overview of the steps required to create a NIRSpec MOS proposal. Additionally, new MOS terminology is defined, and the steps for implementing confirmation images are described. More detailed descriptions of MOS proposal implementation can be found in the NIRSpec MPT - Catalogs, NIRSpec MPT - Planner and NIRSpec MPT - Plans articles, as well as the MOS Roadmap. Likewise, an overview of the multi-phase MOS observing process, from proposal submission to angle assignment and flight-ready updates can be found in the article NIRSpec MOS Observing Process.
Creating a NIRSpec MOS proposal: a basic overview
Like all JWST observations, NIRSpec MOS proposals are created in APT. However, the MOS planning is unlike other APT templates, because users do not simply select a narrow range of parameters in the template. Instead, the MSA Planning Tool (MPT)* is used to generate test plans, which can then be used when filling out the NIRSpec MOS observation template. (A Plan refers to a set of pointings and MSA configurations.)
The basic steps for creating a MOS proposal in APT are as follows (New in APT 2020.1.1):
- Create a Catalog, and upload it in APT's Targets folder by selecting the Import MSA Source Catalog button. This creates a new type of target called a Catalog Target.
- Define appropriate Primary and (optionally) Filler candidate sets with primary sources and filler sources. Filtering the catalog into these candidate sets can be done in the Catalog Target by highlighting the catalog and clicking New Candidate Set.
- Navigate to MPT, which can be found in APT's tool bar (between the Spreadsheet Editor, and HST's Orbit Planner; see Figure 1).
- Use MPT to create a variety of observing Plans, selecting options for nodding and dithering, source centering constraints, and the number of desired configurations in the MPT Planner tab (see Figure 2). For MPT to work, the user must be connected to the internet so MPT can check whether a selected aperture position angle is feasible.
- Use MPT to assess the quality of multiple Plans, and arrive at an estimate of the sample size that can be proposed. This is done in the MPT Plans tab (see Figure 2).
Create an observation using the preferred Plan. Observations created using the MPT will send pointing positions, MSA shutter configurations, and instrument setups to the MOS template.
Fill out the remainder of the observation template, including exposure parameters, and ETC Workbook IDs. Select whether confirmation images are desired.
In addition to the automatic MPT optimization option, the NIRSpec MOS observation template includes an MSA Configuration Editor, where users can create a custom MSA configuration or long slit configuration by clicking to open and close shutters. This editor can be used to modify automatically-generated MSA configurations, or to create new MSA configurations from scratch.
NIRSpec MPT terminology
NIRSpec MOS observing has introduced some new terminology. Table 1 gives the definition of these terms and provides links for more information.
Table 1. Glossary of MSA Planning Tool related terms
|A complete list of sources in the field. This list should include objects of interest for MSA observations and any other objects that could contaminate spectra. The parent catalog will usually contain more sources than are observed in the NIRSpec MOS observations. (Candidate TA reference stars will eventually need to be added after program acceptance and for the design of flight-update programs.) A NIRSpec MOS observation must be created using a single parent catalog.|
A user-created list of sources of interest for MOS spectroscopic observations, derived from the parent catalog. Candidate sets can be subsets of the parent catalog that meet scientific sample selection criteria. They will typically be used as the Primary or Filler candidate lists in MPT. The full parent catalog can also be a candidate set. Minimally, the user must specify a primary candidate set for running MPT.
|Plan||A product from running the MPT for a single set of parameters. Plans contain a list of pointings, MSA configurations, and a table of the MSA sources observed in the MSA configurations.|
|Visit||NIRSpec MOS APT visits within an observation are created by the MPT after clicking Create Observation. Visits are components of an observation that begin with guide star acquisition, followed by target acquisition, and ultimately science exposures and perhaps small angle maneuvers of the telescope. All visits in an observation will execute at the same orient.|
|Observation||NIRSpec MOS observations are sets of visits that are made by the MPT after clicking Create Observation on a preferred Plan or set of Plans. The NIRSpec MOS observation template is populated with many of the required observing parameters. Exposure parameters and other options can be added or edited to fully specify the observation. All visits in an observation will execute at the same orient.|
|MSA Configuration||A set of planned open and closed micro shutters in the MSA for one exposure, or one set of nodded exposures (which uses the same pattern of open/closed shutters). A visit may contain several MSA configurations as needed to complete an MSA observation.|
|Target Set||Subset of sources from the parent Catalog that are observed in all exposures over a complete set of the nods and/or dithers specified in the MPT. A target set can use multiple MSA configurations to achieve dithering. One or more target sets, each containing one or more MSA configurations, may be observed in a single observation. |
A series of adjacent commanded-open micro-shutters in the cross-dispersion direction forming a slit to disperse the light of a given target.
Indicates the 5 choices for the limiting shutter centering margin in the MPT Planner: from tightly constrained to unconstrained.
|Reposition the telescope slightly between exposures to place the targets into different shutters within their respective slitlets in the same MSA configuration.|
|Dither||Telescope offsets used to acquire multiple exposures within a single visit. By definition, dithers require a new MSA configuration, while nods do not.|
Planning NIRSpec MOS confirmation images
NIRSpec MOS Confirmation Images can be acquired through the spectroscopy science filter and the science MSA configuration.
There are 3 available options for acquiring NIRSpec MOS confirmation images in the Obtain Confirmation Image pulldown selection:
No (default): No MOS confirmation images through the open/closed slitlet configurations are acquired at any point in the execution of science exposures.
After Target ACQ: MOS confirmation images are acquired following the conclusion of the NIRSpec target acquisition activity in a visit, and after the MSA and science filter are configured. These images can provide verification of target positioning within the MSA configuration used in a visit. TA executes only once during a visit, so this confirmation image will also be taken just once.
After Target ACQ and New MSA Config: MOS confirmation images are acquired immediately after configuration of the MSA, every time a new MSA slitlet configuration is used. Note: for this option, the grating wheel will move to the imaging mirror to take confirmation images in between science spectra. When the grating wheel is reconfigured to the dispersive element, it might not return to the exact same science position used for prior exposures. As a result, small wavelength shifts can occur between multiple MOS spectra acquired with a confirmation image in-between exposures. However, NIRSpec's grating wheel sensor is designed to remove this shift in the calibration pipeline.
Confirmation images can be planned by selecting the appropriate option in the multi-object spectroscopy pull-down menu in the APT template, as shown in Figure 3. This option should be selected after observations are created in the template by using the MPT.
Karakla, D. et al. 2014, Proc. SPIE 9149
The NIRSpec MSA Planning Tool for multi-object spectroscopy with JWST