NIRSpec Multi-Object Spectroscopy APT Template

NIRSpec's multi-object spectroscopy (MOS) observing mode provides the means to simultaneously obtain the spectra of multiple objects within its 3.4 × 3.6 arcmin overall field of view. Because of the complexity of this mode, the MSA Planning Tool (MPT) within APT was developed to help users create MOS observations.

 Caution: MOS observations are created differently!
The MOS APT Template should not normally be filled out by the user. Instead, the MSA Planning Tool (MPT) should be used.

On this page

Users should not fill out the MOS APT template for most MOS science cases. MPT will automatically fill out the template when an observation is created. To start creating a MOS observation with the MSA Planning Tool, follow the instructions in the MSA Planning Tool, MPT page.

Exceptions to this rule exist for some science cases, in particular, long slit observations of moving targets and/or extended targets. In these cases, the steps shown in the Long Slit Observations article should be followed. Whether or not observations are defined automatically with the MPT, manually designed in the MSA configuration editor, or directly specified in the observation template in special cases, the user should complete the observation template to specify the addition of any confirmation Images, and/or observation special requirements, especially those required for MOS observations described in the MOS Roadmap.

MOS APT template parameters

The NIRSpec multi-object spectroscopy template consists of the following parameters:

FieldDetailsValues Notes

General information

Observation Numberassign observation number


 Observation Label provide observation labeltextoptional
Observation Commentsprovide observation commentstextoptional
Coordinated Parallel checkboxcheck if adding NIRCam or MIRI parallelsNIRCam or MIRI imaging
Targetselect target name from list taken from the Targets folderchoose from list Can be a Moving Target, Fixed Target, or an MSA Catalog Target
Special Requirementsspecify special requirementschoose from listif needed

Target acquisition parameters

TA Methodselect TA methodNONE, MSATA, WATA, VERIFY_ONLY MSATA is required for Catalog Target

MSA target acquisition visit-level selections

Reference Star Binlist of reference stars and configurationchoose from listbins of candidate reference stars are constructed for each TA filter and readout pattern. User must select one bin.
Acq Filterfilter name
 set based on selected Reference star bin
Acq MSA Configurationselect MSA configuration choose Auto Acq MSA Config or ALLOPENdefault is a auto-generated protective MSA configuration for selected reference star bin.
Acq Readout Patternreadout pattern
 set based on selected reference star bin

WATA target acquisition exposure

Acq Targetselect acquisition targetchoose from list
Acq Subarrayselect subarraySUB32, SUB2048, FULL
Acq Filterselect filterF110W, F140X, or CLEAR
Acq Readout Patternselect readout patternNRSRAPID, NRSRAPIDD6

Acq ETC Wkbk. Calc. ID

specify ETC Workbook Calculation IDnumberoptional ETC workbook ID

Pointing verification image

PV Filter

select filter name

choose from list

PV Readout Pattern

select readout pattern

choose from list

PV Groups/Int

specify number of groups/integration

PV MSA Configuration
specify filename or value

choose from list that includes ALLOPEN, ALLCLOSED, Q4 Field Point 1 Long SlitQ4 Field Point 2 Long Slit

Science parameters

Primary Candidate Listselect from available candidate sets defined in the MSA Catalog Target
MPT will populate this
Filler Candidate Listselect from available candidate sets defined in the MSA Catalog Target
MPT  will populate this
Aperture PAPlanned and Assigned angle fields are shown.  Assigned is blank until an angle is assigned by STScI.values from 0 to 360 degreesPlanned aperture position angle is the angle used to run MPT, and is greyed out in the template.  Assigned is the APA given to the observation for making flight updates.
Dither Type (if Coordinated Parallels checkbox is enabled and NIRSpec MOS-NIRCam imaging is selected.)select option for dithers








This option is only available when NIRCam imaging coordinated parallels are included.  Additional small dithers in the cross-dispersion direction improve PSF sampling in the NIRCam imaging.
Science Apertureselect apertureMSA_Center, Q4 Field Point 1, Q4 Field Point 2Select "MSA_Center" for MOS observations planned with MPT.  Other selection options are for use with the pre-defined MSA Long Slit Configurations.

Science exposure specification

Grating/Filterselect grating/filter namechoose from listSelect one grating/filter pair per exposure line
Readout Patternselect readout patternNRS, NRSRAPID, NRSIRS2, NRSIRS2RAPIDselect from one of the traditional or IRS2 readout modes.
Groups/Intspecify number of groups/integrationnumber
Integrations/Expspecify number of integrations/exposurenumber
Autocalselect auto calibration optionchoose from NONE, WAVCAL, FLAT, BOTHNONE is recommended

ETC Wkbk. Calc. ID

specify ETC Workbook Calculation IDnumberoptional

Science configurations/pointings

MSA Configurationselect MSA Configurationchoose from listCustom MSA Configuration, one created using the MSA Planning Tool, or  a pre-defined Long-Slit.
Exposure Specificationselect Grating/Filter combinationchoose from list of Grating/Filter specification in the Exposure Specification table

Indicates the line from the Exposure Specification table that is used for a row in the Configurations/Pointings table.

If generated from an MPT Plan, these will be filled in.


The base pointing.  If the Observation was generated from an MPT Plan, this is the pointing of the exposure.
Dispersion Offset
number in fractional shuttersOffset from base pointing in dispersion direction (X)
Cross-Dispersion Offset
number in fractional shuttersOffset from base pointing in spatial direction (Y) 
Nod Pattern

choose from list when building MOS observation manually

2 shutter slitlet, 3 shutter slitlet, 5 shutter slitlet, 5 shutter slitlet with gaps

If generated from an MPT Plan, these will be filled in
Edit Configclick Edit buttonclick button to edit configurationOption to alter the MSA configuration of one or more exposures. Clicking this will bring up the MSA configuration editor.

Confirmation Image

Obtain Confirmation Imagesspecify if confirmation image desiredchoose After Target Acq or After Target Acq and New MSA Configoption to obtain confirmation images of the science sources in the science slits with the science dispersers.
Confirmation Type  reflects the selection of Obtain Confirmation Images parameter
Conf. Readout Patternselect readout patternNRS, NRSRAPID, NRSIRS2, NRSIRS2RAPIDreadout pattern choices will be a subset depending on the science mode (traditional or IRS2).
Confirmation Groups/Intspecify number of groups/integrationnumber


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



Latest updates

 Updated confirmation image readout patterns

  Added info about "Planned" and "Assigned" Aperture PA