Description¶
- Class
- Alias
tso_photometry
The tso_photometry
step does aperture photometry with a circular aperture
for the target. Background is computed as the mean within a circular annulus.
The output is a table (ASCII ecsv format) containing the time at the
midpoint of each integration and the photometry values.
Assumptions¶
This step is intended to be used for aperture photometry with time-series exposures. Only direct images should be used, not spectra.
The target is assumed to have been placed at the aperture reference location, which is stored in the XREF_SCI and YREF_SCI FITS keywords (note that these are 1-indexed values). Hence the step uses those keyword values as the target location within the image.
Algorithm¶
The Astropy affiliated package photutils
does the work.
If the input file was not averaged over integrations (i.e. a _calints product), and if the file contains an INT_TIMES table extension, the times listed in the output table from this step will be extracted from column ‘int_mid_MJD_UTC’ of the INT_TIMES extension. Otherwise, the times will be computed from the exposure start time, the integration time, and the number of integrations. In either case, the times are Modified Julian Date, time scale UTC.
The output table contains these fields:
MJD
aperture_sum
aperture_sum_err
annulus_sum
annulus_sum_err
annulus_mean
annulus_mean_err
aperture_bkg
aperture_bkg_err
net_aperture_sum
net_aperture_sum_err
Subarrays¶
If a subarray is used that is so small that the target aperture extends beyond the limits of the subarray, the entire area of the subarray will be used for the target aperture, and no background subtraction will be done. A specific example is SUB64 with NIRCam, using PUPIL = WLP8.