phfotran

phfotran measures how your instrumental filters differ from a standard photometric system and writes the transformation table used by phcal --tratab.

Observe a standard field (e.g. Landolt or Stetson) with one frame per filter, prepare the frames as for phcal (astrometry and photometry), and run phfotran on them.

There are two models. The default --model mag fits the familiar colour terms of the magnitudes, filter by filter, comparable to published instrument colour terms. --model flux fits a linear mixing of photon rates, which suits a filter that leaks light from a neighbouring band.

Usage

munipack phfotran [options] file(s)

Options

Option	Argument	Default	Description
-c, --cat	file	—	Reference catalogue of the standard field.
-f, --filters	list	—	Filters, one per frame (paired by FILTER).
-C, --cal	list	1	Factors multiplying the counts, in the order of -f.
-E, --extin	list	0	Extinction coefficients, for a transformation outside the atmosphere.
--col-ra	name	RAJ2000	Right Ascension column.
--col-dec	name	DEJ2000	Declination column.
--col-mag	list	—	Magnitude columns, in the order of -f.
--col-magerr	list	none	Magnitude error columns.
--model	mag, flux	mag	Colour terms of magnitudes, or linear mixing of photon rates.
--color-order	1, 2	1	Order of the colour terms of the mag model.
--photsys-ref	name	—	Standard photometric system of the catalogue.
--photsys-instr	name	PHOTSYS of the frames	Name of your instrumental system.
--area	m²	AREA of the frames	Area of the telescope’s entrance aperture.
--phsystab	file	bundled	Photometric system definitions.
--list	—	—	List the available photometric systems and exit.
--tol	deg	HWHM of the frames	Cross-match radius.
--vocat	file	bundled	VO catalogue configuration (column IDs).
-o, --output	file	phfotran.fits	Output table.
--verbose	—	off	Print the fitted coefficients and scatter.
-h, --help	—	—	Show the help.

Output

One FITS table (phfotran.fits unless -o says otherwise; an existing file is overwritten) with the fitted transformation. Pass it to phcal with --tratab.

Examples

Fit the transformation on the standard field T Phe, then calibrate science frames with it:

munipack phfotran --area 1.86 --photsys-instr DK154 --photsys-ref Johnson \
    -c T_Phe.fits --col-ra RA --col-dec DEC -f B,V,R,I --col-mag B,V,R,I \
    T_Phe_B.fits T_Phe_V.fits T_Phe_R.fits T_Phe_I.fits

munipack phcal --tratab phfotran.fits --photsys-instr DK154 --photsys-ref Johnson \
    -c field.fits --col-ra RA --col-dec DEC -f B,V,R,I --col-mag B,V,R,I \
    field_B.fits field_V.fits field_R.fits field_I.fits

Fit a photon-mixing matrix outside the atmosphere for a camera with a band leak:

munipack phfotran --model flux -E 0.25,0.15,0.10 -c cat.fits --photsys-ref Johnson \
    -f B,V,R --col-mag Bmag,Vmag,Rmag -o tra_flux.fits B.fits V.fits R.fits

Notes

• You need the same number of instrumental and standard filters.

• With -E, the airmass is computed from the observatory coordinates in the headers; without them it is undefined.

• For a strong band mixing, the mag model needs --color-order 2.

• The --photsys-instr name is stored in the table, and phcal --tratab checks that it matches your frames.

• Tables from older versions, written before the mag model existed, are read as flux tables.