Updated radiometric and wavelength calibration of the Juno ultraviolet spectrograph

Juno is a spacecraft in polar orbit around Jupiter, and one of its objectives is to explore the Jovian magnetosphere. Charged particles trapped along the Jovian magnetic field lines may generate auroral emission. The Juno magnetospheric payload is designed to measure the charged particle distributions in the Jovian magnetosphere while remote sensing the related UV-auroral emissions. The ultraviolet spectrograph on Juno (Juno-UVS) is a photon-counting imaging spectrograph designed to observe Jupiter's prominent far-UV auroral emissions in the 68 to 210 nm spectral range. This work presents an improvement on the wavelength and radiometric calibration of Juno-UVS. Ground calibration measurements were reanalyzed by expanding the spectral database ultimately used to produce the instrument spectral pixel size map. This significantly improves the wavelength assignation, up to 4 nm at the longer wavelengths, compared with the previous calibration. Dedicated Juno-UVS observation sequences were made to evaluate the slit-dependent radiometric calibration, which was revised accordingly. This work highlights a slight slit-dependent variation in the radiometric calibration. An additional radiometric correction was established at wavelengths greater than 160 nm using some of UVS's brightest recorded stellar spectra.