Welcome to Sphot’s documentation!

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What is Sphot?

Sphot (“es”-phot, S-PHOT) is a Python package for astronomical image analysis. It is designed to provide a simple and efficient way to perform photometry on galaxy images with overlapping foreground stars. Sphot provides a set of tools to perform “foreground cleaning” on images, i.e., to remove the light from the stars in the image before performing photometry on the galaxies. Some of the major functionalities of Sphot include:

  • Fit PSF models to stars near/on top of a background galaxy

  • Fit a Sersic profile to a galaxy in a crowded stellar field

  • Separate foreground stars and background galaxies

  • Estimate the background/foreground/sky model in a crowded field

  • Perform aperture photometry on galaxies

  • and many more…

Users can choose from a range of interfaces to perform these tasks:

  • A simple, fully-automated commandline script run_sphot

  • The top-level functions sphot.core.run_basefit() and sphot.core.run_scalefit

  • The individual functions in the sphot package to make your own recipe

Each use case is documented in the tutorials section.

When to use Sphot?

Sphot has a simple objectuve: to enable precise and accurate photometry of galaxies seen through crowded, foreground stellar fields. Try Sphot if you are looking to:

  • measure the SED of a background galaxy (z>0.1) seen through a nearby galaxy (z<<0.01)

  • remove a foreground MW star from an image of deep field galaxies

  • fit a Sersic profile to a noisy galaxy image with a bright star in the field

What is required to use Sphot?

Sphot is a python package that depends on major astronomy packages, including Astropy and Photutils. You need at least the following:

  • Python 3.11 or later (due to Astropy compatibility)

  • A cutout image of the target galaxy. If you wish to use multi-band images, each image needs to be pixel-aligned and reprojected onto the same scale.

  • A PSF image for the stars to be removed. The pixel scale of the PSF image should be an integer multiple of the pixel scale of the galaxy image.