External resources#

The following external resources are required and most of them are not bundled within the GitHub repository. All resources must be referenced with the corresponding entries in the env.toml file (see Configuration).

Stars catalogue#

The stars.npy file is provided on the GitHub under the resource directory. This binary file is a sample of the Pickles and Depagne (2010) catalogue. They use stellar equatorial coordinates and proper motions from the Tycho-2 catalog, providing reliable positions and temporal drift; UV magnitudes are derived from spectral fits to multi-band photometry, allowing an estimate of each star’s brightness in the relevant filters. The stars.npy file contains a subset of the full catalogue, with only stars with a magnitude smaller than 10 in the U band, and only the following fields:

  • tyRA: Right ascension [°].

  • tyDE: Declination [°].

  • pmRA: Proper motion in RA [mas/yr].

  • pmDE: Proper motion in Dec [mas/yr].

  • Bt : Tycho-2 B_T magnitude.

  • eBt: Uncertainty on B_T.

  • fBt: Spectrally matched / fitted B_T magnitude.

  • U : Spectrally matched / fitted U magnitude.

This dataset is stored as a NumPy structured array, and can be loaded with the cassini_upyp.geometry.geometry.stars_pickles() function. The array also stores the following fields, that are not part of the original catalogue but are computed for a given observation epoch during the geometric computations:

  • RA_cor : Proper-motion corrected RA at the observation epoch [°].

  • DEC_cor : Proper-motion corrected Dec at the observation epoch [°].

  • XYZ : Unit direction vector in the J2000 frame.

UVIS calibration files#

UVIS calibration files must be available locally and grouped in a single directory.

The required files are:

  • Laboratory calibration: EUV_1999_Lab_Cal.dat and FUV_1999_Lab_Cal.dat

    Those contains the full-slit, low-resolution monochromatic extended-source sensitivity measured in the laboratory (1997, updated 1999), in units of (counts s⁻¹ ) / (kilorayleigh).

  • Calibration time dependance: uvis_calibration_trending_v01_data.sav

  • Flat-field: FLATFIELD_*UV_POSTBURN.txt and FLATFIELD_*UV_PREBURN.txt

    There should be four files, two for each UVIS channel. The two files relates to the flat field before and after the starburn event that occured on 6 June 2002.

  • Flat-field time dependance: *{channel}*ff_modifier*.dat

    Those are the flat-field modifier files. The last 10 characters of the file name should correspond to the spacecraft time.

Calibration files are available on the PDS website page of UVIS in the corresponding directory.

SPICE kernels (geometry)#

SPICE kernels are required to compute observation geometry. Two usage patterns are supported.

Full kernel tree (automatic selection)#

Users may maintain a local SPICE kernel repository with the following directory structure:

spice_kernels/
├─ ck/
├─ fk/
├─ ik/
├─ lsk/
├─ mk/
├─ pck/
├─ sclk/
└─ spk/

When this layout is provided and kernels_dir is set accordingly, the geometry code can automatically search for and load appropriate kernels based on observation time and context, provided that the required kernels are available.

Manual kernel list#

Alternatively, users may explicitly provide the list of SPICE kernels to be loaded when calling geometry-related routines in the form of a single metakernel (.mk) file.

In this mode, kernel selection is fully controlled by the user, and the code will not attempt to discover kernels automatically.