Photometric calibration in the ultraviolet of the Star-Planet Activity Research CubeSat (SPARCS)

The Start-Planet Activity Research CubeSat (SPARCS) is a NASA-funded mission led by Arizona State University, devoted to characterizing the UV emission of low-mass stars. During its one--year mission, SPARCS will observe close to 20 low-mass stars, with the goal of understanding their short and long-term UV variability. SPARCS is expected to be ready for launch in 2025. SPARCS’ payload is a 9-cm telescope paired with two delta-doped CCDs. The data calibration converts the raw instrument counts into an average flux for the two ultraviolet bands (153 - 171 nm, 258 - 308 nm). While the system is only weakly sensitive in the infrared, the target stars are very bright at long wavelengths. This requires careful correction for out-of-band emission. The system is being fully characterized on the ground to provide supporting data for the calibration. The calibration uses observations of very stable white dwarfs to achieve the 10% photometric accuracy requirement in both bands.