Temporal and spatial variations of the absolute reflectivity of Jupiter and Saturn from 0.38 to 1.7 μm with PlanetCam-UPV/EHU^⋆

¹ Departamento de Física Aplicada, Escuela de Ingeniería, Universidad del País Vasco, Plaza Torres Quevedo 1, 48013 Bilbao, Spain
e-mail: inigo.mendikoa@tecnalia.com
² Department of Theory of Signal & Communications, Universidad Carlos III de Madrid, Avenida de la Universidad 30, Leganés, 28911 Madrid, Spain
e-mail: jalopezs@ing.uc3m.es

Received: 4 May 2017
Accepted: 22 July 2017

Abstract

Aims. We provide measurements of the absolute reflectivity of Jupiter and Saturn along their central meridians in filters covering a wide range of visible and near-infrared wavelengths (from 0.38 to 1.7 μm) that are not often presented in the literature. We also give measurements of the geometric albedo of both planets and discuss the limb-darkening behavior and temporal variability of their reflectivity values for a period of four years (2012–2016).

Methods. This work is based on observations with the PlanetCam-UPV/EHU instrument at the 1.23 m and 2.2 m telescopes in Calar Alto Observatory (Spain). The instrument simultaneously observes in two channels: visible (VIS; 0.38–1.0 μm) and short-wave infrared (SWIR; 1.0–1.7 μm). We obtained high-resolution observations via the lucky-imaging method.

Results. We show that our calibration is consistent with previous independent determinations of reflectivity values of these planets and, for future reference, provide new data extended in the wavelength range and in the time. Our results have an uncertainty in absolute calibration of 10–20%. We show that under the hypothesis of constant geometric albedo, we are able to detect absolute reflectivity changes related to planetary temporal evolution of about 5–10%.