potpyri.primitives.absphot

Absolute photometry zeropoint calibration using catalog magnitudes.

Queries Vizier (e.g. PS1) via potpyri.utils.catalogs, matches sources, and fits zeropoint via iterative ODR. Writes ZPTMAG and related keywords to the stack header. Authors: Kerry Paterson, Charlie Kilpatrick.

Functions

find_zeropoint(stack, tel[, log])

Compute and write zeropoint to stack FITS using instrument catalog (e.g. PS1).

Classes

absphot([iterations, sigma])

Zeropoint fitter using catalog magnitudes and iterative sigma clipping.
class potpyri.primitives.absphot.absphot(iterations=5, sigma=5)[source]

Bases: object

Zeropoint fitter using catalog magnitudes and iterative sigma clipping.

Y_band(J, J_err, K, K_err)[source]

Compute Y-band mag and error from J and K (2MASS relation).

Parameters:

  • J (array-like or float) – J magnitude(s) and error(s).

  • J_err (array-like or float) – J magnitude(s) and error(s).

  • K (array-like or float) – K magnitude(s) and error(s).

  • K_err (array-like or float) – K magnitude(s) and error(s).

Returns:

(Y_mag, Y_err).

Return type:

tuple

convert_filter_name(filt)[source]

Map instrument filter names to catalog filter names (e.g. PS1).

Parameters:

filt (str) – Instrument filter keyword (e.g. ‘gG0301’, ‘RG850’).

Returns:

Catalog filter name (‘u’, ‘g’, ‘r’, ‘i’, ‘z’, ‘J’, etc.).

Return type:

str

find_zeropoint(cmpfile, tel, match_radius=<Quantity 2.5 arcsec>, phottable='APPPHOT', input_catalog=None, log=None)[source]

Compute zeropoint from cmpfile photometry and catalog; write to FITS header.

Matches sources to catalog (e.g. PS1), runs iterative ODR fit, and updates ZPTMAG, ZPTNSTAR, ZPTCAT, etc. in the stack FITS.

Parameters:

  • cmpfile (str) – Path to stacked/comparison FITS with SCI and phottable extensions.

  • tel (Instrument) – Instrument instance (for get_catalog).

  • match_radius (astropy.units.Quantity, optional) – Matching radius for catalog. Default is 2.5 arcsec.

  • phottable (str, optional) – FITS extension with photometry table. Default is ‘APPPHOT’.

  • input_catalog (astropy.table.Table, optional) – Pre-loaded catalog; if None, catalog is queried via get_catalog.

  • log (ColoredLogger, optional) – Logger for progress.

Returns:

True if ZPT keywords were written; False if photometry or catalog step did not complete (cmpfile may be unchanged).

Return type:

bool

get_catalog(coords, catalog, filt, log=None)[source]

Query VizieR for catalog magnitudes in a filter around given coordinates.

Parameters:

  • coords (astropy.coordinates.SkyCoord) – Target coordinates (used for region size).

  • catalog (str) – Catalog name (e.g. ‘PS1’, ‘2MASS’).

  • filt (str) – Filter name (e.g. ‘g’, ‘r’, ‘J’).

  • log (ColoredLogger, optional) – Logger for progress.

Returns:

(astropy.table.Table, catalog_name, catalog_ID) or (None, None, None) if query fails.

Return type:

tuple or (None, None, None)

get_minmag(filt)[source]

Return minimum catalog magnitude to use for zeropoint (bright limit).

Parameters:

filt (str) – Filter name.

Returns:

Minimum magnitude (brighter limit).

Return type:

float

get_zeropoint(flux, fluxerr, mag, magerr)[source]

Fit zeropoint (and error) from flux/mag arrays using ODR.

Parameters:

  • flux (array-like) – Object fluxes (e.g. from aperture photometry).

  • fluxerr (array-like) – Flux errors.

  • mag (array-like) – Catalog magnitudes.

  • magerr (array-like) – Catalog magnitude errors.

Returns:

(zeropoint, zeropoint_error).

Return type:

tuple of float

zpt_iteration(flux, fluxerr, mag, magerr, log=None)[source]

Iteratively sigma-clip and fit zeropoint via ODR.

Parameters:

  • flux (array-like) – Object fluxes.

  • fluxerr (array-like) – Flux errors.

  • mag (array-like) – Catalog magnitudes.

  • magerr (array-like) – Catalog magnitude errors.

  • log (ColoredLogger, optional) – Logger for progress.

Returns:

(zeropoint, zeropoint_error, master_mask). master_mask is boolean array of sources used in final fit.

Return type:

tuple

potpyri.primitives.absphot.find_zeropoint(stack, tel, log=None)[source]

Compute and write zeropoint to stack FITS using instrument catalog (e.g. PS1).

Parameters:

  • stack (str) – Path to stacked science FITS file (SCI + APPPHOT extensions).

  • tel (Instrument) – Instrument instance (for catalog and filter).

  • log (ColoredLogger, optional) – Logger for progress and errors.

Returns:

True if ZPT keywords were written; False otherwise (see log).

Return type:

bool