Stage 2 Associations: Technical Specifications

Logical Structure

All stage 2 associations have the following structure. The structure is defined and enforced by the stage 2 schema.

  • Informational Meta Keywords

  • List of products, each consisting of

    • Output product name

    • List of exposure members, each consisting of

      • Filename of the exposure that is a member of this association

      • Type of exposure

      • If present, information about errors from the observatory log

Example Association

The following example will be used to explain the contents of an association:

{
    "asn_type": "image2",
    "asn_rule": "candidate_Asn_Lv2Image",
    "version_id": "20210610t121508",
    "code_version": "1.2.3",
    "degraded_status": "No known degraded exposures in association.",
    "program": "00623",
    "constraints": "DMSAttrConstraint({'name': 'program', 'sources': ['program'], 'value': '623'})\nDMSAttrConstraint({'name': 'is_tso', 'sources': ['tsovisit'], 'value': None})\nDMSAttrConstraint({'name': 'instrument', 'sources': ['instrume'], 'value': 'miri'})\nDMSAttrConstraint({'name': 'detector', 'sources': ['detector'], 'value': 'mirimage'})\nDMSAttrConstraint({'name': 'opt_elem', 'sources': ['filter'], 'value': 'f1130w'})\nDMSAttrConstraint({'name': 'opt_elem2', 'sources': ['pupil', 'grating'], 'value': None})\nDMSAttrConstraint({'name': 'opt_elem3', 'sources': ['fxd_slit'], 'value': None})\nDMSAttrConstraint({'name': 'subarray', 'sources': ['subarray'], 'value': 'brightsky'})\nDMSAttrConstraint({'name': 'channel', 'sources': ['channel'], 'value': None})\nDMSAttrConstraint({'name': 'slit', 'sources': ['fxd_slit'], 'value': None})\nConstraint_Image_Science({'name': 'exp_type', 'sources': ['exp_type'], 'value': 'mir_image'})\nConstraint_Single_Science({'name': 'single_science', 'value': False})\nDMSAttrConstraint({'name': 'asn_candidate', 'sources': ['asn_candidate'], 'value': \"\\\\('o037',\\\\ 'observation'\\\\)\"})",
    "asn_id": "o037",
    "asn_pool": "jw00623_20210610t121508_pool",
    "target": "9",
    "products": [
        {
            "name": "jw00623037001_02101_00001_mirimage",
            "members": [
                {
                    "expname": "jw00623037001_02101_00001_mirimage_rate.fits",
                    "exptype": "science",
                    "exposerr": "null"
                }
            ]
        }
    ]
}

Association Meta Keywords

The following are the informational, meta keywords of an association.

asn_id required

The association id. The id is what appears in the Association Naming

asn_pool required

Association pool from which this association was created.

asn_rule optional

Name of the association rule which created this association.

asn_type optional

The type of association represented. See Association Types

code_version optional

The version of the generator that created this association. Typically this is the version of the jwst python package.

constraints optional

List of constraints used by the association generator to create this association. Format and contents are determined by the defining rule.

degraded_status optional

If any of the included members have an actual issue, as reported by the exposerr keyword, degraded_status will have the value One or more members have an error associated with them. If no errors are indicated, the value will be No known degraded exposures in association.

program optional

Program number for which this association was created.

target optional

Target ID for which this association refers to. JWST currently uses the TARGETID header keyword in the stage 2 exposure files, but there is no formal restrictions on value.

version_id optional

Version identifier. DMS uses a time stamp with the format yyyymmddthhmmss Can be None or NULL

products Keyword

A list of products that would be produced by this association. For stage 2, each product is an exposure. Each product should have one science member, the exposure on which the stage 2 processing will occur.

Association products have two components:

name optional

The string template to be used by stage 2 processing tasks to create the output file names. The product name, in general, is a prefix on which the individual pipeline and step modules will append whatever suffix information is needed.

If not specified, the stage 2 processing modules will create a name based off the name of the science member.

members required

This is a list of the exposures to be used by the stage 2 processing tasks. This keyword is explained in detail in the next section.

members Keyword

members is a list of dictionaries, one for each member exposure in the association. Each member has the following keywords.

expname required

The exposure file name. This must be a filename only, with no path. This file must be in the same directory as the association file, so path is not needed. If path data is included, an exception is raised when loading the association file.

exptype required

Type of information represented by the exposure. Possible values are as follows. Note that this is not the same as the exposure ``EXP_TYPE`` header keyword.

  • science: Primary science exposure. For each product, only one exposure can be science.

  • background: Background exposure to subtract.

  • imprint: Imprint exposure to subtract.

  • sourcecat: The catalog of sources to extract spectra for. Usually produced by calwebb_image3 for wide-field slitless spectroscopy.

  • segmap: The 2D segmentation map used to produce the source catalog. Usually produced by calwebb_image3 for wide-field slitless spectroscopy.

  • direct_image: The direct image used to produce the source catalog.

Editing the member list

As discussed previously, a member is made up of a number of keywords, formatted as follows:

{
    "expname": "jw_00003_cal.fits",
    "exptype": "science",
},

To remove a member, simply delete its corresponding set.

To add a member, one need only specify the two required keywords:

{
    "expname": "jw_00003_cal.fits",
    "exptype": "science"
},