AutoProf Parameters
Here we list all parameters used in the built-in AutoProf methods. The parameters are listed alphabetically for easy searching. For further information, links are included to the individual methods which use these parameters.
ap_axialprof_pa (float, default 0)
Referencing Methods
Description
user set position angle at which to align the axial profiles relative to the global position angle+90, in degrees. A common choice would be “90” which would then sample along the semi-major axis instead of the semi-minor axis.
ap_background_speedup (int, default 1)
Referencing Methods
Description
For large images, this can be millions of pixels, which is not really needed to achieve an accurate background level, the user can provide a positive integer factor by which to reduce the number of pixels used in the calculation.
ap_background_unsharp_lowpass (int, default 3)
Referencing Methods
Description
User provided FFT coefficient cutoff for constructing unsharp image.
ap_badpixel_exact (float, default None)
Referencing Methods
Description
flux value that corresponds to a precise bad pixel flag, all values equal to ap_badpixel_exact will be masked if using the Bad_Pixel_Mask pipeline method.
ap_badpixel_high (float, default None)
Referencing Methods
Description
flux value that corresponds to a saturated pixel or bad pixel flag, all values above ap_badpixel_high will be masked if using the Bad_Pixel_Mask pipeline method.
ap_badpixel_low (float, default None)
Referencing Methods
Description
flux value that corresponds to a bad pixel flag, all values below ap_badpixel_low will be masked if using the Bad_Pixel_Mask pipeline method.
ap_centeringring (int, default 50)
Referencing Methods
Description
Size of ring to use when finding galaxy center, in units of PSF. Larger rings will give the 2D fit more data to work with and allow for the starting position to be further from the true galaxy center. Smaller rings will include fewer spurious objects, and can stop the 2D fit from being distracted by larger nearby objects/galaxies.
ap_ellipsemodel_replacemaskedpixels (bool, default False)
Referencing Methods
Description
If True, a new galaxy image will be generated with masked pixels replaced by the ellipse model values.
ap_ellipsemodel_resolution (float, default 1)
Referencing Methods
Description
scale factor for the ellipse model resolution. Above 1 increases the precision of the ellipse model (and computation time), between 0 and 1 decreases the resolution (and computation time). Note that the ellipse model resolution is defined logarithmically, so the center will always be more resolved
ap_extractfull (bool, default False)
Referencing Methods
Description
Tells AutoProf to extend the isophotal solution to the edge of the image. Will be overridden by ap_truncate_evaluation.
ap_fit_limit (float, default 2)
Referencing Methods
Description
noise level out to which to extend the fit in units of pixel background noise level. Default is 2, smaller values will end fitting further out in the galaxy image.
ap_fluxunits (str, default “mag”)
Referencing Methods
Description
units for outputted photometry. Can either be “mag” for log units, or “intensity” for linear units.
ap_forcing_profile (string, default None)
Referencing Methods
Description
File path to .prof file providing forced photometry PA and ellip values to apply to ap_image_file (required for forced photometry)
ap_guess_center (dict, default None)
Referencing Methods
Description
user provided starting point for center fitting. Center should be formatted as:
{'x':float, 'y': float}
, where the floats are the center coordinates in pixels. If not given, Autoprof will default to a guess of the image center.
ap_guess_psf (float, default None)
Referencing Methods
Description
Initialization value for the PSF calculation in pixels. If not given, AutoProf will default with a guess of 1/ap_pixscale
ap_iso_interpolate_method (string, default ‘lanczos’)
Referencing Methods
Description
Select method for flux interpolation on image, options are ‘lanczos’ and ‘bicubic’. Default is ‘lanczos’ with a window size of 3.
ap_iso_interpolate_start (float, default 5)
Referencing Methods
Description
Use a Lanczos interpolation for isophotes with semi-major axis less than this number times the PSF.
ap_iso_interpolate_window (int, default 3)
Referencing Methods
Description
Window size for Lanczos interpolation, default is 3, meaning 3 pixels on either side of the sample point are used for interpolation.
ap_iso_measurecoefs (tuple, default None)
Referencing Methods
Description
tuple indicating which fourier modes to extract along fitted isophotes. Most common is (4,), which identifies boxy/disky isophotes. Also common is (1,3), which identifies lopsided galaxies. The outputted values are computed as a_i = imag(F_i)/abs(F_0) and b_i = real(F_i)/abs(F_0) where F_i is a fourier coefficient. Not activated by default as it adds to computation time.
ap_isoaverage_method (string, default ‘median’)
Referencing Methods
Description
Select the method used to compute the averafge flux along an isophote. Choose from ‘mean’, ‘median’, and ‘mode’. In general, median is fast and robust to a few outliers. Mode is slow but robust to more outliers. Mean is fast and accurate in low S/N regimes where fluxes take on near integer values, but not robust to outliers. The mean should be used along with a mask to remove spurious objects such as foreground stars or galaxies, and should always be used with caution.
ap_isoband_fixed (bool, default False)
Referencing Methods
Description
Use a fixed width for the size of the isobands, the width is set by ap_isoband_width which now has units of pixels, the default is 0.5 such that the full band has a width of 1 pixel.
ap_isoband_start (float, default 2)
Referencing Methods
Description
The noise level at which to begin sampling a band of pixels to compute SB instead of sampling a line of pixels near the isophote in units of pixel flux noise. Will never initiate band averaging if the band width is less than half a pixel
ap_isoband_width (float, default 0.025)
Referencing Methods
Description
The relative size of the isophote bands to sample. flux values will be sampled at +- ap_isoband_width *R for each radius.
ap_isoclip (bool, default False)
Referencing Methods
Description
Perform sigma clipping along extracted isophotes. Removes flux samples from an isophote that deviate significantly from the median. Several iterations of sigma clipping are performed until convergence or ap_isoclip_iterations iterations are reached. Sigma clipping is a useful substitute for masking objects, though careful masking is better. Also an aggressive sigma clip may bias results.
ap_isoclip_iterations (int, default None)
Referencing Methods
Description
Maximum number of sigma clipping iterations to perform. The default is infinity, so the sigma clipping procedure repeats until convergence
ap_isoclip_nsigma (float, default 5)
Referencing Methods
Description
Number of sigma above median to apply clipping. All values above (median + ap_isoclip_nsigma x sigma) are removed from the isophote.
ap_isofit_fitcoefs (tuple, default None)
Referencing Methods
Description
Tuple of FFT coefficients to use in fitting procedure. AutoProf will attemp to fit ellipses with these Fourier mode perturbations. Such perturbations allow for lopsided, boxy, disky, and other types of isophotes beyond straightforward ellipses. Must be a tuple, not a list. Note that AutoProf will first fit ellipses, then turn on the Fourier mode perturbations, thus the fitting time will always be longer.
ap_isofit_fitcoefs_FFTinit (bool, default False)
Referencing Methods
Description
If True, the coefficients for the Fourier modes fitted from ap_isofit_fitcoefs will be initialized using an FFT decomposition along fitted elliptical isophotes. This can improve the fit result, though it is less stable and so users should examine the results after fitting.
ap_isofit_iterlimitmax (int, default 300)
Referencing Methods
Description
Maximum number of iterations (each iteration adjusts every isophote once) before automatically stopping optimization. For galaxies with lots of structure (ie detailed spiral arms) more iterations may be needed to fully fit the light distribution, but runtime will be longer.
ap_isofit_iterlimitmin (int, default 0)
Referencing Methods
Description
Minimum number of iterations before optimization is allowed to stop.
ap_isofit_iterstopnochange (float, default 3)
Referencing Methods
Description
Number of iterations with no updates to parameters before optimization procedure stops. Lower values will process galaxies faster, but may still be stuck in local minima, higher values are more likely to converge on the global minimum but can take a long time to run. Fractional values are allowed though not recomended.
ap_isofit_losscoefs (tuple, default (2,))
Referencing Methods
Description
Tuple of FFT coefficients to use in optimization procedure. AutoProf will attemp to minimize the power in all listed FFT coefficients. Must be a tuple, not a list.
ap_isofit_perturbscale_ellip (float, default 0.03)
Referencing Methods
Description
Sampling scale for random adjustments to ellipticity made while optimizing isophotes. Smaller values will converge faster, but get stuck in local minima; larger values will escape local minima, but takes longer to converge.
ap_isofit_perturbscale_pa (float, default 0.06)
Referencing Methods
Description
Sampling scale for random adjustments to position angle made while optimizing isophotes. Smaller values will converge faster, but get stuck in local minima; larger values will escape local minima, but takes longer to converge.
ap_isofit_robustclip (float, default 0.15)
Referencing Methods
Description
quantile of flux values at which to clip when extracting values along an isophote. Clipping outlier values (such as very bright stars) while fitting isophotes allows for robust computation of FFT coefficients along an isophote.
ap_isofit_superellipse (bool, default False)
Referencing Methods
Description
If True, AutoProf will fit superellipses instead of regular ellipses. A superellipse is typically used to represent boxy/disky isophotes. The variable controlling the transition from a rectangle to an ellipse to a four-armed-star like shape is C. A value of C = 2 represents an ellipse and is the starting point of the optimization.
ap_isoinit_R_set (float, default None)
Referencing Methods
Description
User set initial semi-major axis length, will override the calculation.
ap_isoinit_ellip_set (float, default None)
Referencing Methods
Description
User set initial ellipticity (1 - b/a), will override the calculation.
ap_isoinit_pa_set (float, default None)
Referencing Methods
Description
User set initial position angle in degrees, will override the calculation.
ap_mask_file (string, default None)
Referencing Methods
Description
path to fits file which is a mask for the image. Must have the same dimensions as the main image.
ap_name (string, default None)
Referencing Methods
Description
Name of the current galaxy, used for making filenames.
ap_plot_sbprof_set_errscale (float, default None)
Referencing Methods
Description
Float value by which to scale errorbars on the SB profile this makes them more visible in cases where the statistical errors are very small.
ap_plot_sbprof_xlim (tuple, default None)
Referencing Methods
Description
Tuple with axes limits for the x-axis in the SB profile diagnostic plot.
ap_plot_sbprof_ylim (tuple, default None)
Referencing Methods
Description
Tuple with axes limits for the y-axis in the SB profile diagnostic plot. Be careful when using intensity units since this will change the ideal axis limits.
ap_psf_deconvolution_iterations (int, default 50)
Referencing Methods
Description
number of itterations of the Richardson-Lucy deconvolution algorithm to perform.
ap_psf_file (string, default None)
Referencing Methods
Description
Optional argument. Path to PSF fits file. For best results the image should have an odd number of pixels with the PSF centered in the image.
ap_radialprofiles_expwidth (bool, default False)
Referencing Methods
Description
Tell AutoProf to use exponentially increasing widths for radial samples. In this case ap_radialprofiles_width corresponds to the final width of the radial sampling.
ap_radialprofiles_nwedges (int, default 4)
Referencing Methods
Description
number of radial wedges to sample. Recommended choosing a power of 2.
ap_radialprofiles_pa (float, default 0)
Referencing Methods
Description
user set position angle at which to measure radial wedges relative to the global position angle, in degrees.
ap_radialprofiles_variable_pa (bool, default False)
Referencing Methods
Description
Tell AutoProf to rotate radial sampling wedges with the position angle profile of the galaxy.
ap_radialprofiles_width (float, default 15)
Referencing Methods
Description
User set width of radial sampling wedges in degrees.
ap_regularize_scale (float, default 1)
Referencing Methods
Description
scale factor to apply to regularization coupling factor between isophotes. Default of 1, larger values make smoother fits, smaller values give more chaotic fits.
ap_sampleendR (float, default None)
Referencing Methods
Description
End radius (in pixels) for isophote sampling from the image. Default is 3 times the fit radius, also see ap_extractfull.
ap_samplegeometricscale (float, default 0.1)
Referencing Methods
Description
growth scale for isophotes when sampling for the final output profile. Used when sampling geometrically. By default, each isophote is 10% further than the last.
ap_sampleinitR (float, default None)
Referencing Methods
Description
Starting radius (in pixels) for isophote sampling from the image. Note that a starting radius of zero is not advised. Default is 1 pixel or 1PSF, whichever is smaller.
ap_samplelinearscale (float, default None)
Referencing Methods
Description
growth scale (in pixels) for isophotes when sampling for the final output profile. Used when sampling linearly. Default is 1 PSF length.
ap_samplestyle (string, default ‘geometric’)
Referencing Methods
Description
indicate if isophote sampling radii should grow linearly or geometrically. Can also do geometric sampling at the center and linear sampling once geometric step size equals linear. Options are: ‘linear’, ‘geometric’, ‘geometric-linear’
ap_saveto (string, default None)
Referencing Methods
Description
Directory in which to save profile
ap_scale (float, default 0.2)
Referencing Methods
Description
growth scale when fitting isophotes, not the same as ap_sample—scale.
ap_set_background (float, default None)
Referencing Methods
Description
User provided background value in flux
ap_set_background_noise (float, default None)
Referencing Methods
Description
User provided background noise level in flux
ap_set_center (dict, default None)
Referencing Methods
Description
user provided fixed center for rest of calculations. Center should be formatted as:
{'x':float, 'y': float}
, where the floats are the center coordinates in pixels. If not given, Autoprof will default to a guess of the image center.
ap_set_psf (float, default None)
Referencing Methods
Description
force AutoProf to use this PSF value (in pixels) instead of calculating its own.
ap_slice_anchor (dict, default None)
Referencing Methods
Description
Coordinates for the starting point of the slice as a dictionary formatted “{‘x’: x-coord, ‘y’: y-coord}” in pixel units.
ap_slice_length (float, default None)
Referencing Methods
Description
Length of the slice from anchor point in pixel units. By default, use init ellipse semi-major axis length
ap_slice_pa (float, default None)
Referencing Methods
Description
Position angle of the slice in degrees, counter-clockwise relative to the x-axis.
ap_slice_step (float, default None)
Referencing Methods
Description
Distance between samples for the profile along the slice. By default use the PSF.
ap_slice_width (float, default 10)
Referencing Methods
Description
Width of the slice in pixel units.
ap_truncate_evaluation (bool, default False)
Referencing Methods
Description
Stop evaluating new isophotes once two negative flux isophotes have been recorded, presumed to have reached the end of the profile.
ap_zeropoint (float, default 22.5)
Referencing Methods
Description
Photometric zero point. For converting flux to mag units.