NEAR-INFRARED PHOTOMETRY OF THE IRREGULAR SATELLITES OF JUPITER AND SATURN

摘要

We present JHK_s photometry of 10 Jovian and four Saturnian irregular satellites, taken with the Near-InfraRed Imager at the 8 m Gemini North Observatory on Mauna Kea, Hawaii. The observed objects have near-infrared colors consistent with C-, P-, and D-type asteroids, although J XII Ananke and S IX Phoebe show weak indications of possible water features in the H filter. The four members of the Himalia family have similar near-infrared colors, as do the two members of the Gallic family, S XX Paaliaq and S XXIX Siarnaq. From low-resolution, normalized reflectance spectra based on the broadband colors and covering 0.4-2.2 μm, the irregular satellites are identified as C-type (J Ⅶ Pasiphae, J Ⅵ Himalia, and S Ⅸ Phoebe), P-type (J Ⅻ Ananke and J XVIII Themisto), and D-type (J Ⅸ Carme and J Ⅹ Sinope), showing a diversity of origins for these objects.