Precision characterization of the TESS CCD detectors: Quantum efficiency, charge blooming and undershoot effects

摘要

NASA's Kepler mission revolutionized the exoplanet field by showing how abundant planets around stars are. The Transiting Exoplanet Survey Satellite (TESS) is the next logical step in searching for planets around nearby bright stars that can be followed up using spectroscopy to measure the planetary masses and atmospheric conditions. TESS was launched successfully in April 2018 as an Astrophysics Explorer mission, and is expected to discover a thousand or more planets that are smaller in size than Neptune. TESS employs four identical wide-field optical CCD cameras with a band-pass of 600 nm-1050 nm to perform differential time-series photometry by monitoring at least 200,000 main sequence stars. The detectors are designed for enhanced sensitivity to the redder wavelengths because it is easier to detect small planets around small red stars. The upper limit of the band-pass cutoff at 1050 nm is driven by the quantum-efficiency curve of the detectors. Exoplanet detection using planetary transits requires very high precision photometry because the occultation causes a dip in the brightness in the order of a few hundred parts per million (ppm). The detector noise should therefore be significantly low. This requires very accurate characterization and minimization of the noise sources. An optical test bench with significantly high photometric stability has been developed to perform precise noise measurements for TESS. In this paper, results from precision characterization techniques developed for the TESS CCD detectors are presented. In particular, the characterization of the absolute quantum efficiency (QE), gain, charge saturation and blooming, undershoot effects, and straps of the CCD detectors are presented.