When running Pandeia as a scriptable python module, different background options are used than with the web client.
The Background API
Within Pandeia, the background is defined by two values in the configuration dictionary: background and background_level. The two values are used in concert to either load a background, or identify a pre-computed background to use in the calculation.
background: is 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 have been pre-generated by the JWST Backgrounds Tool at two 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.
For the Minzodi location, we have also defined a "benchmark" level, which is the Minzodi location on June 19, 2020.
The option for no background is also available:
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 below example is of a JSON-formatted numerical background (as it would appear in the input.json file in a web ETC download) for 1 September 2020, pointing at RA = 18:36:56.2, Dec = -36:46:56.2. The first array contains wavelength values. The second array contains the corresponding background values.