Pandeia Backgrounds

When running Pandeia as a scriptable Python module, different background options are used than with the web client.

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The background API

Within Pandeia, the background is defined by 2 values in the configuration dictionary: background and background_level. The 2 values are used in concert to either load a background, or identify a pre-computed background to use in the calculation.

  • background: either a string defining the name of a background (ecliptic or minzodi, or you can conceivably create your own), or the word none for no background, or a list of arrays forming a spectrum
  • background_level: is either low, medium, or high (or, for the minzodi case, benchmark); it does not need to be specified at all if background is none, or a list of arrays

Canned backgrounds

Canned backgrounds have been pre-generated by the JWST Backgrounds Tool at 2 locations: along the ecliptic at ecliptic coordinates Lat = 90, Lon = 0; and at the Minzodi location (Lat = 266.3, Lon = -50).

The canned backgrounds have been generated at low (10% of max), medium (50% of max), and high (90% of max) background levels as determined from estimating the combined interstellar cirrus, zodiacal light, and internal straylight contributions over the entire period that the locations are in the JWST field of regard.

calculation['background'] = 'ecliptic'
calculation['background_level'] = 'high'

For the minzodi location, we have also defined a benchmark level, which is the minzodi location on June 19, 2023.

calculation['background'] = 'minzodi'
calculation['background_level'] = 'benchmark'

The option for no background is also available:

calculation['background'] = 'none'

Custom backgrounds

Custom backgrounds are a list containing wavelength and flux arrays (denoted by square brackets) that define the background. You can define them yourself, use the JWST Backgrounds Tool to generate them (as the web version of the ETC does), or download a calculation from the web ETC that will have a background filled in and can be run through Pandeia directly.

The example below is of a JSON-formatted numerical background (as it would appear in the "input.json" file in a web ETC download) for the Hubble Deep Field on 1 January 2021, pointing at RA = 12:36:49.4, Dec = +62:12:58. The first array contains wavelength values. The second array contains the corresponding background values.

JSON-formatted numerical background from input.json 
{
    "background":[
        [
            0.5,
            0.6000000238418579,
            0.699999988079071,
            0.800000011920929,
            0.8999999761581421,
            1.0,
            1.100000023841858,
            1.2000000476837158,
            1.2999999523162842,
            1.399999976158142,
            1.5,
            1.600000023841858,
            1.7000000476837158,
            1.7999999523162842,
            1.899999976158142,
            2.0,
            2.0999999046325684,
            2.200000047683716,
            2.299999952316284,
            2.4000000953674316,
            2.5,
            2.5999999046325684,
            2.700000047683716,
            2.799999952316284,
            2.9000000953674316,
            3.0,
            3.0999999046325684,
            3.200000047683716,
            3.299999952316284,
            3.4000000953674316,
            3.5,
            3.700000047683716,
            4.0,
            4.25,
            4.5,
            4.75,
            5.0,
            5.099999904632568,
            5.199999809265137,
            5.300000190734863,
            5.400000095367432,
            5.5,
            5.699999809265137,
            5.900000095367432,
            6.099999904632568,
            6.300000190734863,
            6.5,
            6.699999809265137,
            6.900000095367432,
            7.099999904632568,
            7.300000190734863,
            7.5,
            7.699999809265137,
            7.900000095367432,
            8.100000381469727,
            8.300000190734863,
            8.5,
            8.699999809265137,
            8.899999618530273,
            9.100000381469727,
            9.300000190734863,
            9.5,
            9.699999809265137,
            9.899999618530273,
            10.100000381469727,
            10.300000190734863,
            10.5,
            10.699999809265137,
            10.899999618530273,
            11.100000381469727,
            11.300000190734863,
            11.5,
            11.699999809265137,
            11.899999618530273,
            12.100000381469727,
            12.300000190734863,
            12.5,
            12.699999809265137,
            12.899999618530273,
            13.100000381469727,
            13.300000190734863,
            13.5,
            13.699999809265137,
            13.899999618530273,
            14.100000381469727,
            14.300000190734863,
            14.5,
            14.699999809265137,
            14.899999618530273,
            15.100000381469727,
            15.300000190734863,
            15.5,
            16.5,
            17.5,
            18.5,
            19.5,
            20.5,
            21.5,
            22.5,
            23.5,
            24.5,
            25.5,
            26.5,
            27.5,
            28.5,
            29.5,
            30.5,
            31.0
        ],
        [
            0.1531117285921693,
            0.2092165913789387,
            0.23506451247755927,
            0.24387688791350565,
            0.24277532182701037,
            0.24128830458114275,
            0.22860416522123134,
            0.21303268147031135,
            0.20098598517615573,
            0.1924922915642501,
            0.18400246173584303,
            0.17570808294765167,
            0.16714529742597162,
            0.15614162743260643,
            0.1484705880667788,
            0.14183056987524995,
            0.13591249404165623,
            0.1304210845164106,
            0.12397736659487979,
            0.11803495817387152,
            0.11249905864349247,
            0.10740031792192586,
            0.102681230042769,
            0.09748979929887966,
            0.08843152864684274,
            0.08383024772131081,
            0.08021812654934297,
            0.07729718166281412,
            0.07582572037173775,
            0.07102890629331567,
            0.08614716116587136,
            0.09768449076151914,
            0.13219626400710116,
            0.18107548153244085,
            0.2563870348601526,
            0.35894892058466055,
            0.4866335837361104,
            0.5605877719575548,
            0.6401997260374637,
            0.7294213203582277,
            0.8239250387311442,
            0.932278882645071,
            1.16826423112882,
            1.4378382126473466,
            1.7549381673557565,
            2.1220400518091167,
            2.4701888442368825,
            2.8732659105459053,
            3.3145244692772744,
            3.784674751418082,
            4.291235176486179,
            4.836894573651525,
            5.394606936036856,
            5.940103660309018,
            6.49756823108879,
            7.08616427215754,
            7.698410243853719,
            8.314998562471027,
            8.929024120309064,
            9.565253804089139,
            10.214183564354707,
            10.874046090600674,
            11.545157215546233,
            12.227013688011084,
            12.915451940029303,
            13.61505358560525,
            14.332942966213764,
            15.067246303538738,
            15.824306443039939,
            16.62035356821776,
            17.450674505884653,
            18.268531330320922,
            19.106909052427547,
            20.00727014614531,
            21.012687671471074,
            22.130776824714438,
            23.308607943051438,
            24.55004824997389,
            25.855424223471882,
            27.23250553285639,
            28.698465033630725,
            30.253809628901585,
            31.90325798447872,
            33.6506209487392,
            35.513106219069826,
            37.48364749330286,
            39.57840925292605,
            41.80483155768504,
            44.169993991898785,
            46.683179580219715,
            49.35118129515844,
            55.05436888840708,
            69.4750271039678,
            92.51115043183295,
            123.48097917249477,
            165.0497355389275,
            220.68108372099786,
            294.69274917385354,
            392.2832417959625,
            519.6827932604449,
            683.8513487752906,
            892.2339319665946,
            1153.1756797885548,
            1475.6470710508243,
            1868.0202150734551,
            2339.8924286287597,
            2822.3775818457393,
            1881.7713060461292
        ]
    ]
}


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