PhotEval

PhotEval - Photometric consistency evaluation across overlapping frames

Space Telescope Science Institute

Command Line Usage

PhotEval.py [-h] [-dir DIR] [-filter FILTER] [-exp EXPTIME]
            [-snr MIN_SNR] [-prob MIN_PROB] [-min_n MIN_N] [-o OUTPUT]

Reads all *<FILTER>*.smash.fits catalogs from DIR (default: TabPhot/), filters on exposure time and quality, groups detections by Source_name, and writes a summary table with per-source photometric statistics.

Two sets of magnitude statistics are produced:

• Raw (mag_*): based on phot_mag, which uses a fixed instrumental zero point of 28.

• Corrected (magc_*): phot_mag + MAGZERO - 28, i.e. the true calibrated magnitude using the per-image zero point measured by MagZero. When images have different zero points these corrections matter; the corrected scatter (magc_std) is the meaningful repeatability metric.

The key diagnostic is the scatter (magc_std) relative to the expected photon-noise floor (mag_err_mean) and the reduced chi^2 (chi2_nu_c).

Optional Arguments

-h

Print this help and exit.

-dir DIR

Directory containing the *.smash.fits catalogs (default: TabPhot).

-filter FILTER

Filter string used to select files, e.g. r, N662, N673. Files matching *<FILTER>*req.smash.fits are preferred; if none exist for that filter, *<FILTER>*req.gaia.fits are used instead. Default: r.

-exp EXPTIME

Exposure time to select, in seconds (e.g. 30). If omitted all exposure times are used.

-snr MIN_SNR

Minimum SNR for a detection to be included (default: 10).

-prob MIN_PROB

Minimum SMASH star probability for inclusion (default: 0.5).

-min_n MIN_N

Minimum number of qualifying detections required to include a source in the output (default: 3).

-o OUTPUT

Output FITS filename (default: phot_eval_<FILTER>_<EXPTIME>.fits in the current directory).

-zp_table FILE

FITS table of empirical zero points (e.g. zeropoints.fits produced by CalcZeroPoint). Must contain Filename and zp_calc columns. When supplied, a second set of corrected magnitudes is computed using zp_calc in place of the header MAGZERO, giving additional output columns magc_emp_* and chi2_nu_emp for direct comparison.

Output Columns

Source_name, RA, Dec, n_detect, mag_mean, mag_wmean, mag_median, mag_std, (raw, ZP = 28) magc_mean, magc_wmean, magc_median, magc_std, (corrected, ZP = MAGZERO) magc_emp_mean, magc_emp_wmean, magc_emp_median, magc_emp_std, (empirical ZP, if -zp_table given) mag_err_mean, snr_mean, chi2_nu, chi2_nu_c, chi2_nu_emp

Examples

Evaluate r-band 30-second exposures:

PhotEval.py -filter r -exp 30 -snr 10 -min_n 5

Evaluate Ha (N662) band, all exposure times:

PhotEval.py -filter N662 -min_n 3 -o ha_eval.fits

Compare header MAGZERO vs empirical ZP from CalcZeroPoint:

PhotEval.py -filter r -zp_table zeropoints.fits -o phot_eval_r_emp.fits

Functions

do_eval(tabphot_dir, filter_str, exptime, snr_min, ...)
steer(argv)

Module Contents

PhotEval.do_eval(tabphot_dir, filter_str, exptime, snr_min, prob_min, min_n, outfile, zp_lookup=None, extra_zp_lookups=None, files=None)

PhotEval.steer(argv)