Complete Demo

from hostphot.utils import plot_fits, plot_image
from hostphot.cutouts import download_images
from hostphot.processing import coadd_images
from hostphot.processing import masking
from hostphot.photometry import global_photometry as gp

from astropy.utils.data import clear_download_cache
clear_download_cache()  # saves space in your machine

Due to scheduled system maintenance, the access to eJWST data products might be intermittent on Monday 20th April 2026 from 15:00 to 16:00 CEST. We apologize for the inconvenience.

name = 'SN2002fk'

ra, dec = 50.52379, -15.40089
host_ra, host_dec = 50.527333, -15.400056
z = 0.0075

Host coordinates are used to center the image cutouts and selecting the host.

Cutouts

surveys = ['GALEX', 'PanSTARRS', '2MASS', 'WISE']

for survey in surveys:
    print(survey)
    download_images(name,
                    host_ra,
                    host_dec,
                    survey=survey,
                    overwrite=False,  # saves some time when rerunning
                    save_input=True,  # to be able to replicate the results - True by default
                   )

GALEX
PanSTARRS
2MASS
WISE

Coadds

coadd_images(name, filters='riz', survey='PanSTARRS')

plot_fits("images/SN2002fk/PanSTARRS/PanSTARRS_riz.fits")

Masking

First the coadd to see how it looks

masking.create_mask(name,
                    host_ra,
                    host_dec,
                    filt='riz',
                    survey="PanSTARRS",
                    # masking parameters
                    threshold=12,  # sigmas above bkg to detect sources
                    sigma=6,  # width of the Gaussian kernel
                    r=4,  # to scale the size of the masks
                    # other parameters
                    ra=ra, dec=dec,  # to plot the SN position
                    save_plots=True,  # False by default as it takes some time to create the figure
                    save_mask_params=True,  # to use the output on the other images - False by default
                    save_input=True,  # True by default
                   )

plot_image("images/SN2002fk/PanSTARRS/PanSTARRS_riz_masked.jpg")

Compared to previous versions (< 3.0.0), the “aperture” of the host galaxy is not plotted anymore to avoid confusion as it is not the final aperture.

Applying the mask

Let’s apply the same mask on every filter from every survey.

from hostphot.surveys_utils import get_survey_filters

for survey in surveys:
    filters = get_survey_filters(survey)
    for filt in filters:
        try:
            masking.create_mask(name,
                                host_ra,
                                host_dec,
                                filt=filt,
                                survey=survey,
                                # where to get the mask from
                                ref_filt="riz",
                                ref_survey="PanSTARRS",
                                # let's not waste space and time
                                save_plots=False,  # no need to store these plots as we have the reference
                                save_mask_params=False,
                                save_input=False,
                               )
        except Exception as exc:
            print(f"{survey}-{filt}: {exc}")

Global Aperture

The coadd is used as a reference for the aperture used on the rest of the images.

_ = gp.extract_aperture(name,
                        host_ra,
                        host_dec,
                        filt='riz',
                        survey='PanSTARRS',
                        ra=ra,
                        dec=dec,
                        use_mask=True,  # use the masked image just created
                        optimize_kronrad=True,  # are we "optimising" for DR3? We did for DR2
                        eps=0.001,  # fractional changes in flux when "optimising"
                        gal_dist_thresh=-1,  # how far to go until the host galaxy is found
                        save_aperture_params=True,  # to use the output on the other images - True by default
                        save_plots=True, # to check the results - True by default
                       )

plot_image("images/SN2002fk/PanSTARRS/global_PanSTARRS_riz.jpg")

Global Photometry

for survey in surveys:
    gp.multi_band_phot(name,
                       host_ra,
                       host_dec,
                       survey=survey,
                       ra=ra,
                       dec=dec,
                       use_mask=True,
                       correct_extinction=False,  # no extinction for now
                       # we tell HostPhot to use the "reference" aperture
                       common_aperture=True,
                       ref_survey='PanSTARRS',
                       ref_filt='riz',
                       # let's store only some of the results
                       save_plots=True,
                       save_results=True,  # stores the photometry in a CSV file
                       save_aperture_params=False,
                       raise_exception=False  # in case something goes wrong
                      )

SED

from hostphot.photometry import sed_plotting

name = 'SN2002fk'
sed_plotting.plot_sed(name)