podi_photcalib Module

This module contains all functionality for performing a photometric calibration for a given frame. It does so by matching the ODI source catalog to a catalog of stars from the SDSS. The comparison between instrumental and reference magnitudes then yields the calibration zeropoint.

If requested, podi_photcalib also creates diagnostic plots that allow to easily judge the quality of the obtained calibration.

The module also contains all required functionality to access local SDSS star catalogs or, if no local copies are available, query the SDSS online.

Command line options

• -multi

  Deprecated for now, do not use

• -new

• -querysdss

  Test-routine that queries the SDSS and prints the returned catalog

  Run as:

  podi_photcalib -querysdss ra_min ra_max dec_min dec_max (-print)

  If the -print option is given as well print the entire catalog to stdout, otherwise only print the number of returned stars.

• -swarp

  Compute the photometric zeropoint for a frame created with swarp.

  Run as:

  ‘’podi_photcalib.py -swarp swarped_frame.fits swarp_input_frame.fits``

  swarp_input_frame here is one of the frames that went into the swarped frame. This is necessary to obtain the FILTER and EXPTIME keywords that are required for the photometric calibration, but are typically not contained in the swarped frame any longer.

• -aucap

  Compute the photometric zeropoint for a frame created with the Automatic Calibration Pipeline (AuCaP).

  Run as:

  podi_photcalib.py -aucap file1.fits file2.fits file3.fits ...

  In this mode, podi_photcalib can run on any number of input frames in sequence.

Note for the -aucap and -swarp modi

To save time during programming, two additional flags are supported in these modi. By default, if the source catalog for the specified input file already exists, it is simply re-used and not created. To force re-running SExtractor, add the -resex flag. Additionally, in the -aucap mode, if the source catalog exists, podi_photcalib also does not re-create the diagnostic plots. To change this behavior and re-create the plots, add the -replot flag.

podi_photcalib.load_catalog_from_sdss(ra, dec, sdss_filter, verbose=False, return_query=False, max_catsize=-1)

Query the SDSS online and return a catalog of sources within the specified area

Parameters :

• ra (float[2] (e.g. [165.5, 165.9]) –

  Min and max values for RA

• dec (float[2]) –

  Same as ra, just for declination

• sdss_filter (string (allowed are u,g,r,i,z)) –

  Name of the SDSS filter for which to return magnitudes

• verbose (Bool) –

  Add debugging output

• return_query (Bool) –

  If set to false, the return value also contains the SQL query used to query the SDSS catalog

• max_catsize (int) –

  Maximum number of SDSS stars to be returned

Returns:

• The SDSS catalog, in the format
• Ra, Dec, mag_u, magerr_u, mag_g, magerr_g, ..r, ..i, ..z

podi_photcalib.load_catalog_from_stripe82cat(ra, dec, calib_directory, sdss_filter)

Load the source catalog from the custom pODI Stripe82 catalog.

Parameters :

• ra, dec – float –

  Center position of the search area. The search radius is set to 0.6 deg.

• calib_directory - string –

  directory that contains the Stripe82 catalog

• sdss_filter - string –

  Name of the filter for which the magnitudes should be returned.

Returns:

• A catalog of sources within the search area, stored in an array. Columns
• are as follows. Ra, Dec, mag_median, mag_mean, mag_std, mag_var

podi_photcalib.load_sdss_catalog_from_fits(sdss_ref_dir, ra_range, dec_range, verbose=True)

Retrieve the SDSS catalog for the specified area, using the local FITS-based catalog of the SDSS.

Parameters :

• sdss_ref_dir (string) –

  Directory containing the local copy of the SDSS star catalog. This directory has to contain the catalog index in a file named “SkyTable.fits”

• ra_range (float[2] (e.g. [165.5, 165.9])) –

  Minimum and maximum RA range, in degrees

• dec_range (float[2]) –

  as ra_range, just for declination

• verbose (Bool) –

  add some debugging output useful for error tracking

Returns:

source-catalog –

contains the following columns: ra, dec, mag_u, magerr_u, g, r, i, z

podi_photcalib.photcalib(source_cat, output_filename, filtername, exptime=1, diagplots=True, calib_directory=None, overwrite_cat=None, plottitle=None, otalist=None, options=None, verbose=False, eliminate_flags=True, matching_radius=3)

Perform the photometric calibration, create the diagnostic plots and return the results.

Parameters :

• source_cat (ndarray) –

  Input source array containing the catalog output from the SExtractor run.

• output_filename (string) –

  Filename of the file containing the resulting image file. In the case of collectcells, this is the output filename, hence the name. However, if photcalib is run on existing images, this is the image INPUT filename.

• filtername (string) –

  Name of the ODI filter. Based on this filter name photcalib will decide the corresponding SDSS filter.

• exptime (float) –

  Exposure time of the frame, required to normalize the photometric zero- point.

• diagplots (Bool) –

  If True, create the diagnostic plots for the photometric calibration.

• calib_directory (string)

• overwrite_cat (Bool)

• plottitle (string) –

  Title of the diagnostic plot, e.g. containing the filename, or some information about the Object, etc.

• otalist (HDUList) –

  If given, photcalib uses the WCS information from the individual extensions to add OTA outlines to the global, focal-plane wide diagnostic plot.

• options (dictionary) –

  General options, containing information about some command line flags.

• eliminate_flags (Bool) –

  If set to True, only sources with no SourceExtractor flags (that might indicate problems with the photometry) are used for the calibration. If set, fewer stars are used but these stars are of the best possible quality.

• matching_radius (float) –

  Matching radius to be used when matching the ODI source catalog to the SDSS reference catalog.

Returns:

• ZP-median (float) –

  median zeropoint across the entire focal plane

• ZP-Std (float) –

  standard deviation of the photometric zeropoint

• ODI-SDSS-matched (ndarray) –

  matched catalog of ODI sources and SDSS reference stars.

• ZP-normalized (float) –

  photometric zeropoint, corrected and normalized to an exposure time of 1 second.

podi_photcalib.photcalib_old(fitsfile, output_filename, calib_directory, overwrite_cat=None)

Deprecated, do not use.

podi_photcalib.query_sdss_catalog(ra_range, dec_range, sdss_filter, verbose=False)

High-level interface to the SDSS catalog search. Depending on the settings in podi_sitesetup (see sdss_ref_type) this forwards the query to search either the local Stripe82 catalog, the online SDSS catalog or the local FITS catalog.

Parameters :

• sdss_ref_dir (string) –

  Directory containing the local copy of the SDSS star catalog. This directory has to contain the catalog index in a file named “SkyTable.fits”

• ra_range (float[2] (e.g. [165.5, 165.9])) –

  Minimum and maximum RA range, in degrees

• dec_range (float[2]) –

  as ra_range, just for declination

• verbose (Bool) –

  add some debugging output useful for error tracking

Returns:

source-catalog