Additional STIPS Examples

Below is a condensed example of STIPS usage, similar to the usage in the Basic Tutorial.

It creates a scene from an existing source catalog input_sources.txt, then observes the scene with the Roman WFI F129 filter offset by 0.5 degrees in RA and rotated by 27 degrees:

from stips.scene_module import SceneModule
from stips.observation_module import ObservationModule


scm = SceneModule()

stellar = {
            'n_stars': 100,
            'age_low': 1.0e12, 'age_high': 1.0e12,
            'z_low': -2.0, 'z_high': -2.0,
            'imf': 'salpeter', 'alpha': -2.35,
            'binary_fraction': 0.1,
            'distribution': 'invpow', 'clustered': True,
            'radius': 100.0, 'radius_units': 'pc',
            'distance_low': 20.0, 'distance_high': 20.0,
            'offset_ra': 0.0, 'offset_dec': 0.0

          }

stellar_cat_file = scm.CreatePopulation(stellar)

galaxy = {
            'n_gals': 10,
            'z_low': 0.0, 'z_high': 0.2,
            'rad_low': 0.01, 'rad_high': 2.0,
            'sb_v_low': 30.0, 'sb_v_high': 25.0,
            'distribution': 'uniform', 'clustered': False,
            'radius': 200.0, 'radius_units': 'arcsec',
            'offset_ra': 0.0, 'offset_dec': 0.0
        }

galaxy_cat_file = scm.CreateGalaxies(galaxy)


obs = {
        'instrument': 'WFI',
        'filters': ['F129'],
        'detectors': 1,
        'distortion': False,
        'pupil_mask': '',
        'background': 'avg',
        'observations_id': 1,
        'exptime': 1000,
        'offsets': [{'offset_id': 1, 'offset_centre': False, 'offset_ra': 0.5, 'offset_dec': 0.0, 'offset_pa': 27.0}]
      }

obm = ObservationModule(obs)
obm.nextObservation()

output_stellar_catalogues = obm.addCatalogue(stellar_cat_file)
output_galaxy_catalogues = obm.addCatalogue(galaxy_cat_file)

obm.addError()

fits_file, mosaic_file, params = obm.finalize(mosaic=False)

In this case, the output catalog(s) will show the actual applied count rates. Whether there is only one output catalog or two depends on the input catalog format.

Fast Extended Sources

As of version 2.2, STIPS includes an option to inject extended sources in scenes using a Sersic-profile approximation. This approximation is ~8 times faster than the current implementation, but it is also less accurate.

To activate this feature, users must turn on the fast_galaxy flag. This is how the syntax looks, starting from the examples listed in the STIPS Basic Tutorial.

observation_parameters = {
                          'instrument': 'WFI',
                          'filters': ['F129'],
                          'detectors': 1,
                          'distortion': False,
                          'background': 0.15,
                          'fast_galaxy': True,
                          'observations_id': 1,
                          'exptime': 1000,
                          'offsets': [offset]
                          }

Note

We caution however that while this method is a useful approximation, the resulting integrated flux measurements can be off by a factor of ~2. Furthermore, the central pixel at the core of the galaxy should not be trusted, since this can be off by multiple orders of magnitude.