JWST Multi-Object Spectroscopy Roadmap

A general guide to preparing JWST NIRSpec multi-object spectroscopy (MOS) observations.

On this page

For most MOS science cases, observations are not specified directly in the Astronomers' Proposal Tool (APT) template in the same way as other observing modes. The typical MOS observer will use the NIRSpec MSA Planning Tool (MPT) to create optimal plans for MOS observations that attempt to maximize the number of observed sources. 

Manually designed MOS observations of extended or moving targets that do not use MSATA (MSA target acquisition) will follow a single-phase process. Examples are long slit MOS observations or custom, manually-designed MSA configurations that use WATA (wide aperture target acquisition) for target acquisition (TA). These atypical programs must be finalized at proposal submission. Any constraints on the timing or Aperture Position Angle must be included in the proposal.

Words in bold italics are buttons 
or parameters in GUI tools. Bold 
style represents GUI menus/
panels & data software packages.

Unlike most JWST observing modes, NIRSpec MOS science observations typically follow a two-phase process. This two-phase process is a result of the need for precise target positioning in very tiny shutters in the MSA. After proposal submission and acceptance, an aperture position angle (APA) assignment (called assigned Aperture PA in APT)  is made by STScI schedulers so that the NIRSpec MOS observations can be scheduled more efficiently and flexibly. All programs using MSATA, or which have MOS observations that use an MSA Catalog Target, will follow the two-phase submission process. The nominal MOS process is described in greater detail in the NIRSpec MOS and MSATA Observing Process article. Summarizing here:

(1) In the first phase, "proposal submission", observers will typically run the NIRSpec MSA Planning Tool (MPT) to create a set of planning visits with placeholder pointings and MSA shutter configurations that will be representative of the pointing and configurations after an APA has been assigned. Provided the source density of the catalog is representative, MPT can predict the number of targets to expect for each pointing for a given observing strategy. For proposal submission, it is also important to include any fully specified NIRCam pre-imaging observations that will be used to locate targets for NIRSpec follow-up. Timing links should be included, to ensure that the NIRCam pre-imaging is carried out before the NIRSpec observations, by a sufficient marginIn order to clarify the MOS planning process, a step-by-step roadmap for proposing NIRSpec MOS science is summarized below. Additionally, some useful MOS observational strategies are discussed in the MOS Recommended Strategies article.

(2) The second phase begins after APA assignment and after any NIRCam pre-imaging is obtained. Prior to the first MOS observing window, observers will first update the catalog from any pre-imaging. The placeholder observations/visits will then need to be updated by running MPT once again, utilizing the latest MSA shutter operability information and the assigned APA to design the final MOS program. These observations will specify the exact pointings and MSA configurations, and the expected targets that will be observed. This is called the "program submission" (a.k.a. "program update"). The reference stars used for MSA target acquisition must also be finalized in this submission. The roadmap for planning MOS program updates is described below, following the section on MOS proposals.



Some preliminary notes

Catalogs

NIRSpec observations planned with MPT typically require planning catalogs. Catalogs produced from HST ACS or WFC3 imaging have sufficient relative accuracy for detailed MOS observation planning and program updates. The catalog should be as complete as possible, including not only sources of scientific interest, but all other sources in the field, to be able to identify potential contaminants. The relative astrometric accuracy of the catalog is important for target acquisition to put science sources in the tiny shutters. For example, a relative astrometric accuracy of 5 mas in the catalog is necessary to deliver a NIRSpec MSA target acquisition (MSATA) accuracy of 20 mas. Catalog accuracies of 5–10 mas are required for meaningful use of the centering constraint in MPT which can help to limit slit loss and wavelength calibration uncertainties. Catalogs are not necessary for long-slit observations using the Q4 field points

NIRCam pre-imaging

NIRCam pre-imaging may be needed for MOS observations where imaging and catalogs are either non-existent or of insufficient astrometric accuracy to plan detailed MOS observations. In this case, the observers will use the updated MSA catalog to refine their MOS observations in a program update.

NIRCam or MIRI parallels

Many science cases will benefit from the ability to observe NIRSpec MOS targets while simultaneously imaging nearby fields with NIRCam for future science exploration. Likewise, parallel observations with MIRI could enable expanded science goals. Coordinated parallels with MIRI or NIRCam can be added from the NIRSpec MOS APT template. A set of joint dithers can be added to improve the NIRCam pixel sampling. The MOS Recommended Strategies article discusses this and other useful strategies.

Moving targets 

Consult the generic JWST Moving Target Roadmap. MOS observations of moving targets must be specified directly in the MOS APT template at the observation level. Fill out the template directly, select a pre-designed custom config or the pre-defined long slit, and select the correct science aperture (the Q4 field point should be used with the matching long slit MSA configuration). 

Pre-defined long slit and custom MSA configurations

A pseudo long slit is offered directly in the MOS APT template in the pull-down selector for the MSA configuration. Using the dispersion offset values in the configurations/pointings area of the observation template, it is possible to step the slit sequentially across a large extended target and obtain spectroscopy through the long slit. Similarly, users can create a custom configuration with the MSA Configuration Editor that can be used in the MOS template together with dithers specified in the MSA Configuration Editor to step across a series of smaller extended targets over the MSA field of view. 

MPT performance requirements

MPT has certain memory limits and computational requirements. These are given in the NIRSpec MPT - Computational Performance article.



NIRSpec MOS proposal roadmap

The following roadmap should be used by those who wish to submit a proposal for MOS observations using the NIRSpec micro-shutter array (MSA). The steps outlined here follow those in the Getting Started with JWST ProposingThe program update (second phase submission) follows a similar approach - in that case, observers will replan their MSA observations using an assigned aperture position angle (that will be evident in APT) and also select reference stars for the MOS visits. Consult the NIRSpec MOS Observing Process for a details about this process.

This roadmap assumes the standard use of the MPT to define NIRSpec MOS observations using a Catalog. Details specific to other more specialized cases using pre-defined or custom MSA configurations are presented using the pull-down options shown in the roadmap at various steps. For an example program that uses the standard roadmap, please see the NIRSpec MOS Deep Extragalactic Survey article.

Roadmap for MOS observations (for proposal submission)

  1. Determine the range of feasible MOS observation aperture position angles (Aperture PA) for the field of interest.
    General Target Visibility Tool (GTVT)
    NIRSpec Observation Visualization Tool (NOVT)

  2. An input source catalog is required for MOS observations of multiple distinct sources with the NIRSpec MSA. Obtain or create a source Catalog of sufficient accuracy.
    1. Determine whether HST imaging and source catalogs exist for your fields. If so, obtain one for later use with the MSA Planning Tool (MPT).
      Hubble Space Telescope Finder Images and Catalogs
      Hubble Source Catalog
      MAST
      Vizier

    2. If a catalog derived from HST imaging does not exist, then create a fake Catalog that spans an area of the sky in the field of interest to allow MPT to select optimal pointings. An area of 5' × 5' is suggested. For proposal submission you may use a simulated catalog or one created from observations with other telescopes. The fake catalog should have a similar density and extent to the one that is expected from pre-imaging, in order to get realistic estimates of observing efficiency with different planning strategies.
      NIRSpec MOS Operations - Catalogs and Images
      NIRSpec MPT - Catalogs
      MPT Catalogs - Examples

  3. Decide on a target acquisition strategy based on the positional accuracy needed for your MOS science goalsMOS programs prepared with MPT that use a catalog should use MSATA for target acquisition. However, MSATA doesn't have to be fully specified at proposal submission.
    NIRSpec Target Acquisition
    NIRSpec MSA Target Acquisition
    NIRSpec MOS Operations - Slit Losses

    For extended sources or moving targets, a relaxed accuracy for target acquisition may be possible. For those cases, 

    NIRSpec Wide Aperture Target Acquisition
    NIRSpec Verify Only Target Position

    The MOS observations in these programs can be specified in the APT template directly (without the use of MPT). The MOS observation must be finalized at proposal submission. If a particular orientation is needed, a special requirement restricting the aperture position angle is warranted and should be added to the observation in the proposal.

  4. Optional NIRCam pre-imaging may be requested if existing imaging and source catalogs for your fields of interest do not provide the required positional accuracy for the TA or the science.

    First, check the relative accuracy of your catalog coordinates, and determine if the accuracy delivered by MSATA is sufficient for your science goals.
    NIRSpec MOS Operations - Slit Losses

    If needed, propose for NIRCam pre-imaging in the same proposal as your NIRSpec observations. NIRCam pre-imaging observations must be fully defined at the time of proposal submission.
    NIRCam Pre-Imaging

  5. Pick desired wavelength setting(s) for your MOS observations. Select dispersers and filters, depending on the wavelength coverage and the resolving power required.
    NIRSpec Dispersers and Filters

  6. Determine what dither strategy to use with your NIRSpec MPT-generated MOS observations. Nods and dithers are specified when designing an observation with the MPT Planner, and will appear in the observation template. (Alternatively, nods and dithers can be added directly by specifying them in the Pointings/Configurations table in the observation template, or in the MSA Configuration Editor as described in step 8 for custom MOS observations. Dithers for pre-defined long slit observations can be specified in either of these two ways.)
    NIRSpec Dithers and Nods

  7. Before specifying your NIRSpec MOS observation, learn about recommended practices for dithering, background subtraction, MSA leakage, and general MOS recommendations.
    NIRSpec MOS Recommended Strategies
    NIRSpec Dithering Recommended Strategies
    NIRSpec Background Recommended Strategies
    NIRSpec MSA Leakage Subtraction Recommended Strategies

  8. Create NIRSpec MOS observation plans in APT/MPT. Run the MSA Planning Tool (MPT) in the Astronomers Proposal Tool (APT) to create automatically-designed NIRSpec MOS observations with MPT. Navigate to MPT by clicking the MPT icon in the toolbar of APT. Follow the articles under the MOS APT Template (Catalogs, Planner, and Plans, in that order) from the links shown below to walk through the creation and evaluation of a MOS Plan. An example science case is illustrated in the article NIRSpec MOS Deep Extragalactic Survey.
    NIRSpec MSA Planning Tool, MPT
    NIRSpec Multi-Object Spectroscopy APT Template
    NIRSpec MPT - Catalogs
    NIRSpec MPT - Planner
    NIRSpec MPT - Plans

    OR  create a MOS observation using the pre-defined MSA Quad 4 long slit

    • Your NIRSpec MOS long slit observation can be specified directly In the Astronomers Proposal Tool (APT) template. The Target of the observation should be a moving target or extended fixed target selected from the Targets folder in APT.

    • WATA is the default TA strategy, but you may select a different TA option (VERIFY_ONLY or NONE). None of these options use reference stars.

    • The default Science Aperture for the long slit is the Q4 field point 1. Specify your exposure parameters, and be sure to select the Q4 Field Point 1 Long Slit configuration together with the corresponding Q4 Field Point science aperture to center your target in the slit at the defined reference point for that aperture. 
      Long Slit MOS Observations

    • If desired, specify additional exposures with different dispersion offsets in the Pointings/Configurations table of the Science Parameters section of the MOS template. Using the same long slit configuration, these offsets can be used to step the slit across an extended source in the dispersion direction, for example. The offsets are in units of shutters, and the MSA shutter pitch is ~0.27 arcsec.
      MOS Recommended Strategies


    • For the initial exposure, check that the target is centered in the long slit at the defined reference point and assigned APA. The long slit associated with Q4 Field Point 1 is located at column 250 in Q4 (quadrant 4). For a fixed source, display an image of the source in Aladin, and highlight the observation to see the footprint of the MSA. Select the FoV icon to see the 4 quadrants of the MSA. The target should be centered near the top left of Q4.
      APT Aladin Viewer

    • Fill out the remainder of the MOS Observation template in APT (refer to step 13).

    • These observations will likely require an Aperture PA special requirement to limit the range of position angles. Be sure to add one, if needed (refer to step 15). MOS observations of moving targets may need added special requirements to limit the timing in order to place aperture position angle constraints based on the orientation of the target. These observations will follow a single stream process, so observers will not have a chance to replan at a later time.

    • Continue from step 12 onward.

    OR  create a MOS observation using custom MSA configurations

    • If making a custom MOS observation using a catalog, first select an exact pointing and orientation. It may be helpful to view an image of your target(s) in Aladin, and to overlay your MSA Catalog Target source positions there.
      JWST APT Aladin Viewer

    • When returning from Aladin, click the Form Editor icon to be able to see the MOS observation template.

    • MOS observations that use a catalog will need to use the MSATA target acquisition method. These observations will later get an assigned APA after program acceptance and will follow the two-phase process that will provide an opportunity to re-plan the observation in a program update after an APA assignment.
      NIRSpec MSA Target Acquisition

    • Navigate to the MSA Configuration Editor, and create or import your custom MSA configuration planned at a fixed pointing that you determined. Continue to add exposure specifications using the same MSA configuration, and include any dispersion or cross-dispersion offsets in the MSA Configuration Editor, or in the table showing Pointings/Configurations in the Observation template.
      Custom MOS Observations using the MSA Configuration Editor

    • Specify the Pointing associated with your MSA configuration. If no pointing is specified in the Pointings/Configurations table of the MOS APT template, the pointing will be the reference position of the MSA Catalog Target used for the observation. Additionally, dithers in the dispersion and/or cross-dispersion direction can be specified in this table. Use these offsets to, for example, step the slit across the sources in the dispersion direction. Nods in the cross-dispersion direction can be added in the Nod Pattern column as well. To do so, click the Nod Pattern cell in the Configurations/Pointings table row and select one of the nod patterns from the pull-down menu.
      MOS Recommended Strategies


    • Evaluate the observation in MPT. These plans can be evaluated in the Plans tab of MPT, just like auto-generated MPT plans.
      NIRSpec MPT - Plans

    • When returning from MPT or Aladin, click the Form Editor icon to be able to see the observation template. Be sure the correct manually-designed MSA configuration is shown in the Configurations/Pointings table in the observation template.

    • Because the custom MSA configuration required the use of an MSA Catalog Target, the MOS observation will get an assigned APA, and therefor a two-phase submission process. If needed, you may restrict the assigned Aperture Position Angle with an APA special requirement in the proposal (refer to step 15).
      Special Requirements

    • Continue from step 11.
  9. The MPT should be run at several available APAs to check the variation in plan results and obtain more informed estimates of the observing time needed to execute the science. Multiplexing depends on a wide range of factors: the catalog density, extent, source distribution, the slit shape used, source centering constraints, etc. Multiplexing mostly does not depend on aperture position angles for catalogs distributed randomly. However, cases that involve a handful of highly weighted sources may be impacted by the selected angle. The user should test different angles and planning strategies in any case. 
    NIRSpec MPT - Parameter Space

  10. Create an MPT Observation. Once you have an MPT plan that you are happy with, click Create Observation from the Plans pane in MPT to populate the NIRSpec MOS mode observation template with pointings, MSA configurations and exposure parameters.
    NIRSpec MPT - Plans
    NIRSpec Multi-Object Spectroscopy APT Template

  11. Return to the MOS Observation template in APT by clicking the Form Editor icon. Note that MSA target acquisition (MSATA) reference alignment targets, called reference stars, and related TA parameters for the science observations cannot be defined at proposal submission because the Aperture PA isn’t yet assigned. The selection of reference stars and MSATA parameters is done after the MOS observations are finalized. Leave this for the detailed program update submission. 

  12. Determine the required exposure and detector readout parameters for your NIRSpec MOS observations including target acquisitions using the Exposure Time Calculator (ETC). Perform these calculations by bracketing the range of expected source brightnesses in the wavelength bands of interest, avoiding saturation of the brightest sources. ETC workbooks are provided for each instrument mode to illustrate parameter selection. Example science programs each provide a page to describe the ETC calculations for that example.
    NIRSpec Detector Recommended Strategies
    JWST ETC Target Acquisition
    Understanding Exposure Times
    NIRSpec Example Science Programs

  13. In the MOS observation template, specify the correct exposure duration parameters for your science observation in your MOS observation (Readout Pattern, Groups/Integration, and Integrations).
    Understanding Exposure Times

  14. Continue to fill out the remaining elements of the MOS APT template, including the decision to add Confirmation Images to be able to locate targets in the slitlets in post-analysis.
    NIRSpec MOS Operations - Confirmation Images

  15. Determine from viewing in Aladin, or with NOVT, whether an Aperture PA special requirement is needed. The NIRSpec MOS observation should ideally not have a specific Aperture PA special requirement added. However, some use cases may need such constraints. For scheduling flexibility, a minimum range of approximately 20°–30° is recommended. Observation planning using a catalog with MPT or a manually created plan uses an Aperture PA, however this angle is not guaranteed for the observation, nor is it used downstream to plan or schedule the observation. However, the Aperture PA assigned by STScI will be enforced for program update submission. 
    NIRSpec MOS Operations - Pre-Imaging Using NIRCam
    NIRSpec Observation Visualization Tool (NOVT)
    Aperture Position Angle Special Requirements
    APT Aladin Viewer

  16. A timing special requirement is needed when NIRCam pre-imaging is requested in the same program.

    When NIRCam pre-imaging is specified in the proposal,

    The MOS observation should have a Timing special requirement (specifically, an AFTER BY <observation link>added to ensure enough time is allowed between NIRCam pre-imaging and NIRSpec follow-up observations. The recommended minimum is 60 days, but 42 days is the absolute minimum, leaving only 2 weeks for the observing team to complete program updates. The NIRSpec Observation Visualization Tool (NOVT) can be used to visualize and help plan the pre-imaging observations relative to the NIRSpec observation.

    NIRSpec MOS Operations - Pre-Imaging Using NIRCam
    Timing Special Requirements
    NIRSpec MOS and MSATA Observing Process
    NIRSpec Observation Visualization Tool (NOVT)

  17. Add optional NIRCam or MIRI coordinated parallels, if desired. View the footprints of any parallels in APT in the Aladin viewer using the FOV button and by highlighting the NIRSpec observation. Select single aperture if the view is too crowded. If the NIRCam parallels are specified with joint subpixel dither options, make sure the NIRSpec exposure time is appropriate. Note that some joint subpixel dither options will double or triple the number of NIRSpec dithers, and may require adjustment of the MOS exposure duration parameters.
    Coordinated Parallel Observations
    JWST Coordinated Parallels Custom Dithers
    APT Aladin Viewer

  18. The APT Visit Planner should be run to check the scheduling of the MOS visits created by the MPT.  The APT graphical timeline may be useful for examining the layout of your MOS observation.
    APT Visit Planner
    APT Graphical Timeline

  19. Your proposal is now ready for submission.


NIRSpec MOS program update

The following roadmap should be used by those who need to submit a program update for MOS observations. The information below follows from steps outlined in the Getting Started with JWST Proposing articleThe program update (the second phase of the MOS submission process) follows a similar approach to the proposal submission. In this phase, observers will replan their MSA observations using an assigned Aperture Position Angle (that will be populated for the user in APT) and will also select reference stars for the MOS visits. Consult the NIRSpec MOS Observing Process for a details about this process.

This roadmap assumes the standard use of the MPT to define NIRSpec MOS observations using a Catalog. Details specific to other more specialized cases using pre-defined or custom MSA configurations are presented at various steps in the roadmap using the pull-down options shown. For an example program that uses the standard roadmap, please see the NIRSpec MOS Deep Extragalactic Survey article.

Roadmap for program update of MOS observations

  1. Before re-planning your MOS observation, familiarize yourself with any recent updates to the MOS process, recommended strategies, or target acquisition.
    NIRSpec MOS and MSATA Observing Process
    MOS Recommended Strategies
    Background Recommended Strategies
    MSA Leakage Subtraction Recommended Strategies
    Moving Target Recommended Strategies
    NIRSpec Target Acquisition
    NIRSpec MSA Target Acquisition


  2. If pre-imaging was specified in your proposal, a Catalog produced by, or derived from, the NIRCam imaging pipeline should be used. The NIRCam pipeline-produced catalog should be available in the MAST archive. If no pre-imaging was requested, you may already have produced an HST-derived catalog for the proposal submission.
    MAST

    Hubble Space Telescope Finder Images and Catalogs
    Hubble Source Catalog

  3. Mark suitable reference stars candidates for MSATA in the Catalog. For MSA target acquisition using reference stars, 4 additional columns must now be added to the Catalog. These columns should be labeled NRS_F110W, NRS_F140X, NRS_CLEAR, and REFERENCE. The columns starting with "NRS" should contain the AB magnitudes of each source in each of the NIRSpec TA filters. Suitable candidates should have ABmags in the range from 18th to 25th magnitude. The REFERENCE column should have a value of TRUE when a source is a good candidate reference star (i.e., isolated, and of suitable brightness), and FALSE otherwise. Read the NIRSpec MSATA Reference Star Selection Recommended Strategies article which describes the criteria for suitable reference star candidates and strategies for estimating their magnitudes in the NIRSpec TA filters.
    NIRSpec MSA Target Acquisition
    NIRSpec MSATA Reference Star Selection Recommended Strategies

  4. Input the catalog as a new MSA Catalog Target into the APT Targets folder. 
    NIRSpec MPT - Catalogs

    MPT Catalogs - Examples


  5. Examine your MOS observation(s) in APT. If an assigned Aperture PA has been provided for your program by STScI and is indicated in the observation template, any MOS observations prepared with a different angle will be flagged as needing an update.
    NIRSpec Multi-Object Spectroscopy APT Template

  6. If you are preparing your program using MPT, and have an existing MOS observation that you like, you can now simply replan it in MPT using the assigned APA using the Replan button on the Plans pane of MPT. Note however, It is often possible to improve results by exploring different planning strategies in MPT. Investing some time in trying different strategies can result in more efficient observations with more highly-weighted sources. MPT results depend on a wide range of factors: the catalog density and extent, the source distribution, the search parameters, the number and spacing of dithers, the slit shape used, source centering constraints, etc. Changes to the observations (e.g., number of dithers and exact positions) are expected and allowed, to optimize results for the new assigned angle. In testing new plans, first determine whether changes to your dither strategy are needed for your NIRSpec MPT-generated MOS observations. Nods and dithers are normally specified in the MPT Planner, which allows MPT to flexibly select the best pointings for those dithers. Alternatively, nods and dither offsets can be added after the fact in the MOS observation template (or even using the MSA Configuration Editor for custom MOS observations, described below).
    NIRSpec Dithers and Nods
    NIRSpec Dithering Recommended Strategies
    NIRSpec Multi-Object Spectroscopy APT Template
    NIRSpec MSA Planning Tool, MPT
    NIRSpec MPT - Catalogs
    NIRSpec MPT - Planner
    NIRSpec MPT - Plans

    OR  re-plan your custom MOS observation at the assigned APA

    • Follow the steps above in this roadmap to update and ingest the Catalog, including adding columns needed for reference star selection as described in step 3 above.

    • After an Aperture PA is assigned, observers must re-plan their custom MOS observations and submit a program update. The assigned Aperture PA should appear in the Science Parameters section of the template. Observers will need to re-design their custom MSA configurations at the new angle. Small pointing changes are allowed at this stage.  

    • Make changes to the MSA Configuration(s) from your proposal using the updated MSA Catalog, and the assigned APA. Follow the steps in the proposal roadmap above, in particular - the second pull-down panel of step 8 which describes the use of the MSA Configuration Editor to design a new MSA Configuration.
      JWST APT Aladin Viewer

    • Verify the parameter selections in the Exposure Specification and Configurations/Pointings tables in the Science Parameters section of the template. Check that the Pointings match the pointings at which the MSA configurations were planned. You may wish to add or remove some exposures in these tables.
      Custom MOS Observations using the MSA Configuration Editor
      MOS Recommended Strategies

    • Reference stars will need to be selected for each visit, as described below in this roadmap. Continue with the following steps in this roadmap.
  7. When you have determined the best plan in MPT (either the updated plan from the placeholder observation, or one you have re-designed), then update the MOS observation. To do so, highlight the observation in the APT tree that you wish to replace. Then, select the preferred plan in the Plans pane of MPT, and click Update Observation there to apply the selected plan to the observation. 

    For most MOS programs, the program update must be finalized in time for the submission 6 weeks in advance of the observation plan window start time. Note that the shutter operability will evolve with time. APT will indicate when there are shutter conflicts due to evolving shutter status for planned observations. If MPT is not needed for your observation, make the changes you need in your program to use the assigned angle. Changes to your observing strategy are allowed in many cases, as long as you keep within your total allocated time. Some changes require approval, e.g. changes that could cause duplications with other programs (like changes in filters, gratings, etc.) Your program coordinator will alert you if approval is needed for a change.
    MSA shutter operability

  8. Using the updated catalog source brightnesses, check the exposure and detector readout parameters for your NIRSpec MOS science observations and TA exposures using the Exposure Time Calculator (ETC). Perform these calculations by bracketing the range of expected source brightnesses in the wavelength bands of interest, avoiding saturation of the brightest sources. ETC workbooks are provided for each instrument mode to illustrate parameter selection. 
    NIRSpec Detector Recommended Strategies
    JWST ETC Target Acquisition 

  9. In the MOS observation template, update or specify the correct exposure duration parameters for your science observation in your MOS observation (Readout Pattern, Groups/Integration, and Integrations).
    Understanding Exposure Times

  10. MOS observations that use an MSA Catalog Target are required to use the MSATA methodology with selected reference stars for each visit. This is so that the sources can be positioned accurately into their planned slitlets in the MSA configurations. To select reference stars for each visit, first pull down the Observation folder and highlight the first visit in the hierarchical tree (the left panel of the APT GUI). APT will display a view of the MSA shutters. If there are sufficient suitable reference stars designated in the catalog that are covered by the MSA footprint at the initial pointing in the visit, and are in operable shutters, there will be one or more reference star bins available for selection in the pull-down menu. Make a selection from the Reference Star Bin pull-down menu. The reference star positions should then appear in the shutter view as small black boxes. Eight candidate reference stars are nominal (5 is the minimum). Usually, the top item in the pull-down menu is the recommended selection. Selecting a bin will cause the selection of the MSATA readout pattern and filter. The default is to use the automatically-generated MSA configuration for the imaging associated with MSATA, which is meant to prevent persistence from bright objects that are in the MSA. This is suitable for most cases. This selection process must be repeated for each visit of the MOS observation to fully define the observation.
    NIRSpec MSA Target Acquisition
     

  11. Add optional NIRCam or MIRI coordinated parallels, if they were requested in the accepted proposal. View the footprints of any parallels in APT in the Aladin viewer. Highlight the NIRSpec observation and click the View in Aladin button in the APT toolbar. Use the FOV button in the Aladin to see the footprints. Select single aperture if the view is too crowded.  
    Coordinated Parallel Observations
    APT Aladin Viewer

  12. Select a joint dither option, if it was specified in the accepted proposal. If the NIRCam parallels are specified with joint subpixel dither options, you may need to adjust the NIRSpec exposure time as appropriate. Some joint subpixel dither options will double or triple the number of NIRSpec dithers.  
    JWST Coordinated Parallels Custom Dithers
    Coordinated Parallel Dither Tables

  13. Check Confirmation image parameters if these were specified in your proposal to make sure they are suitable. Confirmation images are not allowed with added parallels at this time.
    NIRSpec MOS Operations - Confirmation Images

  14. Run the APT Visit Planner for the updated observation.  
    APT Visit Planner

  15. Check that the data rate and data volume limits are not violated. Resolve any errors that may appear in the program.
    JWST Data Volume and Data Excess

  16. Your program update is now ready for submission. Deadlines for cycle 1 are outlined in the NIRSpec MOS and MSATA Observing Process article.
    NIRSpec MOS and MSATA Observing Process



References

Karakla, D. et al. 2014, Proc. SPIE 9149
The NIRSpec MSA Planning Tool for multi-object spectroscopy with JWST 




Latest updates

  • Added a few links.

  •   
    Added roadmap for MOS updates. Removed text regarding MOS mosaics, which has been removed from the template. Replaced instructions for the Manual Config Editor (in MPT) with text for the MSA Configuration Editor (at the observation level). Corrected the descriptions of the manual MOS observations and the process they will follow depending on whether MSATA is indicated.

  •  
    Corrected old Manual Planner terminology, removed specifics about MOS Process timing, added a link to new article plus formatting changes 


  • Added link to NIRSpec MSATA Reference Star Selection Recommended Strategies
Originally published