Local Photometry

Everything related to local photometry is documented bellow:

hostphot.local_photometry.choose_cosmology(cosmo)

Updates the cosmology used to calculate the aperture size.

Parameters

cosmo (astropy.cosmology object) – Cosmological model. E.g. FlatLambdaCDM(70, 0.3)().

hostphot.local_photometry.calc_aperture_size(z, ap_radius)

Calculates the size of the aperture in arsec, for aperture photometry, given a physical size.

Parameters

  • z (float) – Redshift.

  • ap_radius (float) – Physical aperture size in kpc.

Returns

radius_arcsec – Aperture size in arcsec.

Return type

float

hostphot.local_photometry.extract_aperture_flux(data, error, px, py, radius)

Extracts aperture photometry of a single image.

Parameters

  • data (array) – Image data in a 2D numpy array.

  • error (array) – Errors of data.

  • px (float) – x-axis pixel coordinate of the aperture center.

  • py (float) – y-axis pixel coordinate of the aperture center.

  • radius (float) – Aperture radius in pixels.

Returns

  • raw_flux (float) – Aperture photometry (“raw” flux).

  • raw_flux_err (float) – Uncertainty on the aperture photometry.

hostphot.local_photometry.plot_aperture(data, px, py, radius_pix, img_wcs, outfile=None)

Plots the aperture for the given parameters.

Parameters

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

  • px (float) – X-axis center of the aperture in pixels.

  • py (float) – Y-axis center of the aperture in pixels.

  • radius_pix (float) – Aperture radius in pixels.

  • img_wcs (WCS) – Image’s WCS.

  • outfile (str, default None) – If given, path where to save the output figure.

hostphot.local_photometry.photometry(name, ra, dec, z, filt, survey, ap_radii=1, bkg_sub=False, use_mask=True, correct_extinction=True, save_plots=True)

Calculates the local aperture photometry in a given radius.

Parameters

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

  • ra (float) – Right Ascensions in degrees to center the aperture.

  • dec (float) – Declinations in degrees to center the aperture.

  • z (float) – Redshift of the object to estimate the physical calculate of the aperture.

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

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

  • ap_radii (float or list-like, default 1) – Physical size of the aperture in kpc.

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

  • 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).

  • save_plots (bool, default True) – If True, the figure with the aperture is saved.

Returns

  • mags (list) – Aperture magnitudes for the given aperture radii.

  • mags_err (list) – Aperture magnitude errors for the given aperture radii.

hostphot.local_photometry.multi_band_phot(name, ra, dec, z, filters=None, survey='PS1', ap_radii=1, bkg_sub=False, use_mask=True, correct_extinction=True, save_plots=True)

Calculates the local aperture photometry for multiple filters.

Parameters

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

  • ra (float) – Right Ascensions in degrees to center the aperture.

  • dec (float) – Declinations in degrees to center the aperture.

  • z (float) – Redshift of the object to estimate the physical calculate of the aperture.

  • 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.

  • ap_radii (float or list-like, default 1) – Physical size of the aperture in kpc.

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

  • 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).

  • save_plots (bool, default True) – If True, the a figure with the aperture is saved.

Returns

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

Return type

dict

Examples

>>> import hostphot.local_photometry as lp
>>> ap_radii = [3, 4]  # aperture radii in units of kpc
>>> ra, dec =  308.22579, 9.92853 # coords of SN2004eo
>>> z = 0.0157  # redshift
>>> survey = 'PS1'
>>> results = lp.multi_band_phot(name, ra, dec, z,
                        survey=survey, ap_radii=ap_radii,
                        use_mask=True, save_plots=True)