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Align astronomical images of point sources. Based on the astroalign Python package.

Credit: Beroiz, M., Cabral, J. B., & Sanchez, B. (2020)

Warning

This package is still in the experimental stage. If you notice an issue, please feel free to let us know!

Installation

pkg> add Astroalign

Getting Started

img_aligned, params = align(img_to, img_from;
    box_size,
    ap_radius,
    min_fwhm = box_size .÷ 5,
    nsigma = 1,
    f = Astroalign.PSF(),
)

See the accompanying Pluto.jl notebook for more.

Contributing

Issues and pull requests welcome.

API / Reference

Astroalign.align_frame — Function
function align_frame(img_to, img_from;
    [box_size],
    [ap_radius],
    [f],
    [min_fwhm],
    [nsigma],
)

Align img_from onto img_to. See below for keyword arguments currently available to control this process.

  • box_size: The size of the grid cells (in pixels) used to extract candidate point sources to use for alignment. Defaults to a tenth of the greatest common denominator of the dimensions of img_to. See Photometry.jl > Source Detection Algorithms for more.
  • ap_radius: The radius of the apertures (in pixel) to place around each point source. Defaults to 60% of first(box_size). See Photometry.jl > Aperture Photometry for more.
  • f: The function to compute within each aperture. Defaults to a 2D Gaussian fitted to the aperture center. See the Source characterization section of the accompanying Pluto.jl notebook for more.
  • min_fwhm: The minimum FWHM (in pixels) that an extracted point source must have to be considered as a control point. Defaults to a fifth of the width of the first image. See PSFModels.jl > Fitting data for more.
  • nsigma: The number of standard deviations above the estimated background that a source must be to be considered as a control point. Defaults to 1. See Photometry.jl > Source Detection Algorithms for more.
source
Astroalign.get_sources — Function
get_sources(img; box_size = nothing, nsigma = 1)

Extract candidate sources in img according to Photometry.Detection.extract_sources. By default, img is first sigma clipped and then background subtracted before the candidate sources are extracted. box_size is passed to Photometry.Background.estimate_background, and nsigma is passed to Photometry.Detection.extract_sources. See the Photometry.jl documentation for more.

TODO: Pass more options to clipping, background estimating, and extraction methods in Photometry.jl.

source