Interactive python wrapper for point-spread fitting (PSF) photometry using Astropy/photutils. Full python (including all dependencies)
Please cite Nicholl et al 2023
To run: python psf.py [--options]
Required inputs (see example directory):
-
transient coordinates, either by -c [RA DEC] or a 1 line, 2-column tab-separated text file ending in '_coords.txt'. RA and Dec should be in decimal degrees
-
list of coordinates of nearby stars (with magnitudes if zero point is required). This is in a file ending '_seq.txt'. If no sequence star file is provided, code will attempt to generate one automatically by querying catalogs (currently using PanSTARRS, SDSS, 2MASS). The format is:
ra dec g r i z
336.7148649 17.1512778 19.188 18.454 18.153 18.031
...
Results will be saved in a directory called 'PSF_output' using a text file with a unique timestamp.
Full list of options available with -h. Some handy ones...
Specifying data / workflow:
-i IMAGES : specify images to analyse (accepts wildcards). Otherwise runs on all fits images in directory
-b BAND : include only images in given band(s) (e.g. '-b g r' will only use g and r images)
--quiet : no user prompts, run in the background
--savefigs : save plots (one per image, showing background, PSF, zeropoint)
--force : do not allow re-centroiding when performing final PSF fit to transient (generally not needed but useful if there is a bright nearby source or you have an exact position)
Pre-processing:
--clean : cosmic ray cleaning with LACosmic
--stack : stack images in same filter
--time-bins N : cadence in days to use for stacked images (defaults to 1 day, i.e. stack from same night only)
--overwrite-stacks : if not given and stacks already exist for desired band and time, will use those rather than making new ones
Calibration
--queryrad N: radius to search for sequence stars in PS1/SDSS/2MASS (default 5 arcmin)
--magmin / magmax MAG : faintest / brightest sequence stars to include in zero point calculation
--aprad N : fixed aperture size in pixels to use for photometry (this is in addition to PSF photometry and optimal aperture photometry)
--apfrac N.N : fraction of the PSF flux to include when calculating optimal aperture size (default is to use an aperture that captures 90% of PSF flux)
--fwhm N : for instances where too few stars to build a PSF, give the default FWHM in pixels to use for a simple Gaussian model
Image subtraction:
--sub : perform template subtraction. Will subtract a local image called 'template_[band].fits' if it exists, otherwise will try to create one from PS1/SDSS
--template: if provided with a filename, uses specified file rather than the default template image above
--templatesize N: side length of PS1/SDSS cutout to download, in arcmin (default 10 arcmin)
--cutoutsize : size of image to cutout for template subtraction, in pixels (default 1000). Provide two numbers to give separate x, y lengths for rectangular stamps