Auxiliary tools

This section describes various procedures that make use of auxiliary numina scripts that support the scientific analysis of images obtained with FRIDA.

Among these tools we can highlight the following:

  • numina-compare_adr_extensions_in_3d_cube: this script computes the correction for differential atmospheric refraction present in a 3D data cube, by reading the information from two specific extensions (e.g., ADRCROSS, ADRTHEOR).

  • numina-compute_adr_wavelength: this script calculates the effect of atmospheric refraction, using a predefined wavelength as reference.

  • numina-extract_2d_slice_from_3d_cube: extracts a 2D section from a 3D FITS image. It allows specifying the axis to collapse and the interval (pixel range) along that axis.

  • numina-generate_mosaic_of_2d_images: this script generates a mosaic of 2D images from a list of 2D FITS files.

  • numina-generate_mosaic_of_3d_images: this script generates a mosaic of 3D data cubes from a list of 3D FITS files.

    • It is possible to use arguments to fix the desired outupt celestial 2D WCS, as well as the output CRVAL3 and CDELT3 parameters that define the output linear wavelength sampling.

    • If the input is a single 3D FITS cube, the code can be used to resample the initial cube with different values of CRVAL3 and CDELT3. In that case, it is recommended to use interp as the reprojection method to avoid the default Gaussian kernel used when the reprojection method is adaptive).

  • numina-imath3d: performs basic arithmetic operations with FITS images (addition, subtraction, multiplication, division) from the terminal command line.

  • numina-measure_slice_xy_offsets_in_3d_cube: this script calculates the spatial offset in the sky plane between a particular spatial slice and all the spatial slices of a given 3D cube. It does so using a cross-correlation method.

  • numina-pixel_solid_angle_arcsec2: this script calculates the solid angle subtended by a pixel in a 2D FITS image (in arcsec^2).

  • numina-pixel_to_world: auxiliary script to convert from pixel coordinates to celestial coordinates and wavelength. There is also the script numina-world_to_pixel, which performs the inverse transformation.

  • numina-resample_wave_3d_cube: this script resamples a 3D data cube by specifying the output values for CRVAL3, CDELT3 and NAXIS3. The celestial WCS is preserved, and the spectral WCS is modified in order to make use of the new wavelength sampling. This code does not use the functionality of the reproject package and instead performs a simple linear redistribution of the signal in the newly sampled wavelength grid. In this sense, it produces the same result as the numina-generate_mosaic_of_3d_images script when employed with a single input 3D FITS file and the reprojection method is interp.

  • numina-sp3d_with_ds9: this script opens a 3D FITS image in the ds9 image browser and allows interactive selection of object and sky spaxels. Simultaneously, the corresponding spectra and their subtraction are displayed. This interaction is similar to what is done with the program qfitsview. The reason for developing this code has been the more comfortable interaction with the Matplotlib window displaying the spectra, along with the ability to leverage the full functionality of the ds9 program. The ds9 session is launched automatically when running this script and must be closed manually upon completion.

  • numina-ximshow: this is a tool for visualizing 2D FITS images using Matplotlib, which can be convenient when displaying multiple images consecutively and quickly saving the result to a PNG or PDF file.

Some of these tools are employed in the examples described in following procedures: