Near-Infrared photometry of Neptune’s small regular satellites with Keck

Abstract

We present data and images that provide insight on the infrared photometry and reflectivity of five of Neptune’s small, regular moons: Proteus, Despina, Galatea, Larissa, and Naiad. Data were taken in the H-band (1.485–1.781μm) on October 07, 2021 from the Keck telescope on Maunakea, Hawaii using the NIRC2 instrument with adaptive optics. We applied a shift-and-stack procedure that allowed us to enhance the signal to noise ratio on each moon as it moved across the detector frame-by-frame. We applied an aperture photometry method to these stacked images in order to extract the flux density and reflectivity of each moon. We find that the H-band albedo of Proteus, Larissa, Galatea, and Despina is the same within one standard deviation, with values near 0.13. The brightness of Naiad is somewhat lower, with a geometric albedo of 0.072±0.013. Comparing these findings with previous observations at visible and infrared wavelengths, we find that four of the five observed moons display a slight spectral reddening from visible to near-infrared wavelengths.