Utils

epsf.utils.download_jwst1pass(overwrite=False)

Download all FITS files from JWST1PASS library

Downloads to EPSF_PATH/jwst1pass if EPSF_PATH env var is set, otherwise to ~/.local/share/epsf/jwst1pass

Parameters:

overwrite (bool) – If True, use timestamping to update existing files. If False, skip existing files.

epsf.utils.get_cutout(img, pos, half_size)

Get a cutout from an image around a given position.

Parameters:

• img (ndarray) – Array to take a cutout from with shape (Ny, Nx)

• pos (tuple[int, int]) – indices of the x and y positions around which to take a cutout

• half_size (int) – Half-size of the cutout to extract

Returns:

Returns a copy of the desired cutout from the original image

Return type:

ndarray

epsf.utils.get_epsf_data_path()

Get the EPSF data directory path

Returns EPSF_PATH env var if set, otherwise ~/.local/share/epsf

Returns:

Path to EPSF data directory

Return type:

Path

epsf.utils.get_final_img(img, final_size, pos_int=None)

Get a cutout with size final_size around a given position in an image. This is very similar to get_cutout(). get_cutout() was written to extract a wider array from a full-frame image while this function was written to extract the final, small cutout from a single-PSF image.

Concretely, the main differences are that get_cutout() requires a position and an half_size, while here we use the final size of the image and take the middle pixel by default.

Parameters:

• img (ndarray) – Array to take a cutout from with shape (Ny, Nx)

• final_size (int) – Final size of the cutout, in pixels

• pos – indices of the x and y positions around which to take a cutout. Take the central pixel if None. Defaults to None.

• pos_int (tuple[int] | None)

Returns:

Returns a copy of the desired cutout from the original image.

Return type:

ndarray

epsf.utils.open_jwst_image(path, pos_cut=None, half_size_cut=None, final_size=None, recenter=True)

Open a JWST image with uncertainties

Parameters:

• path (Path) – Path to a JWST cal file (output of the stage 2 image pipeline).

• pos_cut (tuple[int, int] | None) – Rough position of the target in the full-frame image. Used to center a first cutout.

• half_size – Half size of the first cutout taken from the full-frame image in pixels.

• final_size (int | None) – Size of the final image to return in pixels.

• recenter (bool) – Refine the centroid after the first cutout if True. Uses photutils.centroids.centroid_quadratic().

• half_size_cut (int | None)

Returns:

Science image and associated uncertainties (SCI and ERR extensions).

Return type:

tuple[ndarray, ndarray]

epsf.utils.radec2seppa(ra, dec)

Convert RA and Dec to separation and position angle (PA)

PA = 0 is along the Y axis (north) and RA increases to the left (east)

Parameters:

• ra (float | ndarray) – RA in mas

• dec (float | ndarray) – Dec in mas

Returns:

Separation and PA in mas and deg, respectively

Return type:

tuple[float | ndarray]

epsf.utils.seppa2radec(sep, pa)

Convert separation and position angle (PA) to RA and Dec

PA = 0 is along the Y axis (north) and RA increases to the left (east)

Parameters:

• sep (float | ndarray) – Separation in mas

• pa (float | ndarray) – Position angle in deg

Returns:

RA and Dec in mas

Return type:

tuple[float | ndarray]