SedFluxer

Introduction

SedFluxer is a class with a number of convenience functions to measure fluxes from images in fits format input by the user. get_flux() reads the header and does units transformation, provided that the header is correct, else get_raw_flux() does not do any units transformation and gives the results in raw units so the user can perform their own units transformation.

Starting the SedFluxer object

First of all we need to initialise an SedFluxer object with a loaded fits file, i.e., with a 2D array that is the image and a header. There are various ways to load in a fits file, either from your local disk using, e.g. astropy.io.fits or from archives loaded (and downloaded if desired) into a python variable, e.g., using astroquery, in particular, ESASky or SkyView:

>>> from sedcreator import SedFluxer
>>> fluxer = SedFluxer(hdu)

Once the SedFluxer is initialised, we can now measure fluxes performing aperture photometry by either using get_flux() for automatic unit transformation based on the header or get_raw_fux() to make our own unit transformation. These functions need central coordinates, which are astropy.SkyCoord type, the aperture radius, inner annulus radius, and outer annulus radius given in arcsec:

>>> flux = fluxer.get_flux(central_coords,aper_rad,inner_annu,outer_annu)
>>> #or
>>> flux = fluxer.get_raw_flux(central_coords,aper_rad,inner_annu,outer_annu)

With this flux object, one can retrieve the values for the background subtracted flux and the total flux, as well as the estimation for the fluctuation error and background. One can also print useful information from the header and parameters used and plot the image used together with the aperture and annulus defined:

>>> flux_bkg_sub,flux,flu,bkg = flux.get_value()
>>> flux.plot()
>>> flux.info

The data used in this example can be accessed at this link <https://github.com/fedriani/sedcreator/tree/main/examples/AFGL2591_data>

Below is given a short example:

>>> from sedcreator import SedFluxer
>>> from astropy.utils.data import get_pkg_data_filename
>>> from astropy.io import fits as pyfits
>>> from astropy.coordinates import SkyCoord
>>> import astropy.units as u

>>> filename = '../examples/AFGL2591_data/AFGL2591_Herschel_70.fits'

>>> hdu = pyfits.open(filename)[1]

>>> AFGL2591_coords = SkyCoord(ra='20h29m24.8916s', dec='+40d11m19.388s', frame='fk5')
>>> AFGL2591_fluxer = SedFluxer(hdu)

>>> aperture_radius = 25.0#arcsec
>>> AFGL2591_H70_gt = AFGL2591_fluxer.get_flux(central_coords=AFGL2591_coords,
...                                                aper_rad=aperture_radius,inner_annu=1.0*aperture_radius,
...                                                outer_annu=2.0*aperture_radius)

The plot should look like:

>>> AFGL2591_H70_gt.plot(cmap='rainbow')
_images/AFGL2591_opt_aper_fluxer.png

And printing the info:

>>> AFGL2591_H70_gt.info  
The aperture used is 25.0 arcsec
pixel scale is 3.2 arcsec/pixel
~ 7.812 pixels are used for the aperture radius
units in the image are: Jy/pixel
Regarding observing time:
You are probably using HERSCHEL, look at the first extension of the header
Regarding wavelength:
You are probably using HERSCHEL or ALMA, look at the first extension of the header
############################
Flux bkg sub 4445.462065581253 Jy
Flux         4618.421490377294 Jy
Error Flux   68.13966691325624 Jy
Background   172.95942479604037 Jy
############################

And finally retrieve the fluxes (background subtracted, and without background subtraction) for our own calculations (and use with the SedFitter class):

>>> flux_bkg_sub,flux, flu, bkg = AFGL2591_H70_gt.get_value()
>>> print(flux_bkg_sub,flux,flu,bkg)  
4445.462065581253 4618.421490377294 68.13966691325624 172.95942479604037