The Caviar software package for the astrometric reduction of Cassini ISS images: description and examples⋆,⋆⋆
1 Astronomy Unit, School of Physics and Astronomy, Queen Mary University of London, Mile End Road, London E1 4NS, UK
2 IMCCE, Observatoire de Paris, PSL Research Univ., UMR 8028 du CNRS, UPMC, Université de Lille 1, 77 av. Denfert-Rochereau, 75014 Paris, France
3 Department of Astronomy, Cornell University, Ithaca, NY 14853, USA
4 Department of Computer Science, Jinan University, 510632 Guangzhou, PR China
Received: 4 August 2017
Accepted: 13 October 2017
Aims. Caviar is a software package designed for the astrometric measurement of natural satellite positions in images taken using the Imaging Science Subsystem (ISS) of the Cassini spacecraft. Aspects of the structure, functionality, and use of the software are described, and examples are provided. The integrity of the software is demonstrated by generating new measurements of the positions of selected major satellites of Saturn, 2013–2016, along with their observed minus computed (O−C) residuals relative to published ephemerides.
Methods. Satellite positions were estimated by fitting a model to the imaged limbs of the target satellites. Corrections to the nominal spacecraft pointing were computed using background star positions based on the UCAC5 and Tycho2 star catalogues. UCAC5 is currently used in preference to Gaia-DR1 because of the availability of proper motion information in UCAC5.
Results. The Caviar package is available for free download. A total of 256 new astrometric observations of the Saturnian moons Mimas (44), Tethys (58), Dione (55), Rhea (33), Iapetus (63), and Hyperion (3) have been made, in addition to opportunistic detections of Pandora (20), Enceladus (4), Janus (2), and Helene (5), giving an overall total of 287 new detections. Mean observed-minus-computed residuals for the main moons relative to the JPL SAT375 ephemeris were − 0.66 ± 1.30 pixels in the line direction and 0.05 ± 1.47 pixels in the sample direction. Mean residuals relative to the IMCCE NOE-6-2015-MAIN-coorb2 ephemeris were −0.34 ± 0.91 pixels in the line direction and 0.15 ± 1.65 pixels in the sample direction. The reduced astrometric data are provided in the form of satellite positions for each image. The reference star positions are included in order to allow reprocessing at some later date using improved star catalogues, such as later releases of Gaia, without the need to re-estimate the imaged star positions.
Key words: astrometry / methods: data analysis / techniques: image processing / planets and satellites: general
The Caviar software is available for free download from: ftp://ftp.imcce.fr/pub/softwares/caviar.
Full Tables 1 and 5 are only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (188.8.131.52) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/610/A2
© ESO, 2018