PSF¶
-
class
gunagala.psf.
PSF
(FWHM, pixel_scale=None, **kwargs)[source]¶ Bases:
astropy.modeling.Fittable2DModel
Abstract base class representing a 2D point spread function.
Used to calculate pixelated version of the PSF and associated parameters useful for point source signal to noise and saturation limit calculations.
Parameters: - FWHM : astropy.units.Quantity
Full Width at Half-Maximum of the PSF in angle on the sky units.
- pixel_scale : astropy.units.Quantity, optional
Pixel scale (angle/pixel) to use when calculating pixellated point spread functions or related parameters. Does not need to be set on object creation but must be set before before pixellation function can be used.
Attributes Summary
FWHM
Full Width at Half-Maximum of the PSF. n_pix
The PSF’s effective number of pixels for the worse case where the PSF is centred on the corner of a pixel. peak
The maximum fraction of the total signal that can fall in a single pixel. pixel_scale
Pixel scale used when calculating pixellated point spread functions or related parameters. Methods Summary
pixellated
([size, offsets])Calculates a pixellated version of the PSF. Attributes Documentation
-
FWHM
¶ Full Width at Half-Maximum of the PSF.
Returns: - FWHM : astropy.units.Quantity
Full Width at Half-Maximum in angle on the sky units.
-
n_pix
¶ The PSF’s effective number of pixels for the worse case where the PSF is centred on the corner of a pixel.
The effective number of pixels is for signal to noise calculations for PSF fitting photometry. The signal to noise for PSF fitting photometry is the same as if the signal were evenly distributed over this many pixels.
Returns: - n_pix : astropy.units.Quantity
Effective number of pixels
-
peak
¶ The maximum fraction of the total signal that can fall in a single pixel.
This is simply the central pixel value of the PSF when it is perfectly centred on a pixel centre. This is useful for saturation limit calculations.
Returns: - peak : astropy.units.Quantity
Maximum fraction of the total signal that can fall in a single pixel, in 1/pixel units.
-
pixel_scale
¶ Pixel scale used when calculating pixellated point spread functions or related parameters.
Returns: - pixel_scale : astropy.units.Quantity
Pixel scale in angle on the sky per pixel units.
Methods Documentation
-
pixellated
(size=21, offsets=(0.0, 0.0))[source]¶ Calculates a pixellated version of the PSF.
The pixel values are calculated using 10x oversampling, i.e. by evaluating the continuous PSF model at a 10 x 10 grid of positions within each pixel and averaging the results.
Parameters: - size : int, optional
Size of the pixellated PSF to calculate, the returned image will have
size
xsize
pixels. Default value 21.- offset : tuple of floats, optional
y and x axis offsets of the centre of the PSF from the centre of the returned image, in pixels.
Returns: - pixellated : numpy.array
Pixellated PSF image with
size
bysize
pixels. The PSF is normalised to an integral of 1 however the sum of the pixellated PSF will be somewhat less due to truncation of the PSF wings by the edge of the image.