Global Photometry

Everything related to global photometry is documented bellow:

hostphot.global_photometry.kron_flux(data, err, gain, objects, kronrad, scale)

Calculates the Kron flux.

Parameters

  • data (2D array) – Data of an image.

  • err (float or 2D array) – Background error of the images.

  • gain (float) – Gain value.

  • objects (array) – Objects detected with sep.extract().

  • kronrad (float) – Kron radius.

  • scale (float) – Scale of the Kron radius.

Returns

  • flux (array) – Kron flux.

  • flux_err (array) – Kron flux error.

hostphot.global_photometry.optimize_kron_flux(data, err, gain, objects, eps=0.0001)

Optimizes the Kron flux by iteration over different values. The stop condition is met when the change in flux is less that eps.

Parameters

  • data (ndarray) – Data of an image.

  • err (float or ndarray) – Background error of the images.

  • gain (float) – Gain value.

  • objects (array) – Objects detected with sep.extract().

  • eps (float, default 0.0001 (0.1%)) – Minimum percent change in flux allowed between iterations.

Returns

  • opt_flux (float) – Optimized Kron flux.

  • opt_flux_err (float) – Optimized Kron flux error.

  • opt_kronrad (float) – Optimized Kron radius.

  • opt_scale (float) – Optimized scale of the Kron radius.

hostphot.global_photometry.extract_kronparams(name, host_ra, host_dec, filt, survey, ra=None, dec=None, bkg_sub=False, threshold=10, use_mask=True, optimize_kronrad=True, eps=0.0001, save_plots=True)

Calculates the aperture parameters for common aperture.

Parameters

  • name (str) – Name of the object to find the path of the fits file.

  • host_ra (float) – Host-galaxy right ascension of the galaxy in degrees.

  • host_dec (float) – Host-galaxy declination of the galaxy in degrees.

  • filt (str or list) – Filter to use to load the fits file. List is commonly used for coadds.

  • survey (str) – Survey to use for the zero-points and pixel scale.

  • ra (float, default None) – Right ascension of an object, in degrees. Used for plotting the position of the object.

  • dec (float, default None) – Declination of an object, in degrees. Used for plotting the position of the object.

  • bkg_sub (bool, default False) – If True, the image gets background subtracted.

  • threshold (float, default 10) – Threshold used by sep.extract() to extract objects.

  • use_mask (bool, default True) – If True, the masked fits files are used. These must have been created beforehand.

  • optimize_kronrad (bool, default True) – If True, the Kron radius is optimized, increasing the aperture size until the flux does not increase.

  • eps (float, default 0.0001 (0.1%)) – Minimum percent change in flux allowed between iterations when optimizing the Kron radius.

  • save_plots (bool, default False) – If True, the mask and galaxy aperture figures are saved.

Returns

  • gal_obj (array) – Galaxy object.

  • img_wcs (WCS) – Image’s WCS.

  • kronrad (float) – Kron radius.

  • scale (float) – Scale for the Kron radius.

hostphot.global_photometry.photometry(name, host_ra, host_dec, filt, survey, ra=None, dec=None, bkg_sub=False, threshold=10, use_mask=True, correct_extinction=True, aperture_params=None, optimize_kronrad=True, eps=0.0001, save_plots=True)

Calculates the global aperture photometry of a galaxy using the Kron flux.

Note: the galaxy must be ideally centred in the image.

Parameters

  • name (str) – Name of the object to find the path of the fits file.

  • host_ra (float) – Host-galaxy right ascension of the galaxy in degrees.

  • host_dec (float) – Host-galaxy declination of the galaxy in degrees.

  • filt (str) – Filter to use to load the fits file.

  • survey (str) – Survey to use for the zero-points and pixel scale.

  • ra (float, default None) – Right ascension of an object, in degrees. Used for plotting the position of the object.

  • dec (float, default None) – Declination of an object, in degrees. Used for plotting the position of the object.

  • bkg_sub (bool, default False) – If True, the image gets background subtracted.

  • threshold (float, default 10) – Threshold used by sep.extract() to extract objects.

  • use_mask (bool, default True) – If True, the masked fits files are used. These must have been created beforehand.

  • correct_extinction (bool, default True) – If True, corrects for Milky-Way extinction using the recalibrated dust maps by Schlafly & Finkbeiner (2011) and the extinction law from Fitzpatrick (1999).

  • aperture_params (tuple, default None) – Tuple with objects info and Kron parameters. Used for common aperture. If given, the Kron parameters are not re-calculated

  • optimize_kronrad (bool, default True) – If True, the Kron radius is optimized, increasing the aperture size until the flux does not increase.

  • eps (float, default 0.0001 (0.1%)) – Minimum percent change in flux allowed between iterations when optimizing the Kron radius.

  • save_plots (bool, default True) – If True, the mask and galaxy aperture figures are saved.

Returns

  • mag (float) – Aperture magnitude.

  • mag_err (float) – Error on the aperture magnitude.

hostphot.global_photometry.multi_band_phot(name, host_ra, host_dec, filters=None, survey='PS1', ra=None, dec=None, bkg_sub=False, threshold=10, use_mask=True, correct_extinction=True, common_aperture=True, coadd_filters='riz', optimize_kronrad=True, eps=0.0001, save_plots=True)

Calculates multi-band aperture photometry of the host galaxy for an object.

Parameters

  • name (str) – Name of the object to find the path of the fits file.

  • host_ra (float) – Host-galaxy right ascension of the galaxy in degrees.

  • host_dec (float) – Host-galaxy declination of the galaxy in degrees.

  • filters (str, default, None) – Filters to use to load the fits files. If None use all the filters of the given survey.

  • survey (str, default PS1) – Survey to use for the zero-points and pixel scale.

  • ra (float, default None) – Right ascension of an object, in degrees. Used for plotting the position of the object.

  • dec (float, default None) – Declination of an object, in degrees. Used for plotting the position of the object.

  • bkg_sub (bool, default False) – If True, the image gets background subtracted.

  • threshold (float, default 10) – Threshold used by sep.extract() to extract objects.

  • use_mask (bool, default True) – If True, the masked fits files are used. These must have been created beforehand.

  • common_aperture (bool, default True) – If True, use a coadd image for common aperture photometry.

  • coadd_filters (str, default riz) – Filters of the coadd image. Used for common aperture photometry.

  • optimize_kronrad (bool, default True) – If True, the Kron radius is optimized, increasing the aperture size until the flux does not increase.

  • eps (float, default 0.0001 (0.1%)) – Minimum percent change in flux allowed between iterations when optimizing the Kron radius.

  • save_plots (bool, default True) – If True, the mask and galaxy aperture figures are saved.

Returns

results_dict – Dictionary with the object’s photometry and other info.

Return type

dict

Examples

>>> import hostphot.global_photometry as gp
>>> name = 'SN2004eo'
>>> host_ra, host_dec = 308.2092, 9.92755  # coords of host galaxy of SN2004eo
>>> ra, dec =  308.22579, 9.92853 # coords of SN2004eo
>>> results = gp.multi_band_phot(name, host_ra, host_dec,
                        survey=survey, ra=ra, dec=dec,
                        use_mask=True, common_aperture=True,
                        coadd_filters='riz', save_plots=True)