High resolution on-sky spectroscopy calibrated with a partially stabilized 15-GHz astrocomb from 550–890-nm

Summary form only given. Astronomical spectrographs combining high resolution (R >> 10, 000) with high stability provide unique scientific capabilities, e.g. for observing the small Doppler shifts which are signatures of Earth-like exoplanets or sensitively measuring isotopic ratios in ancient stars to reveal details of the early universe. Laser frequency combs with mode spacings from 12.5-50 GHz [1] have been shown to offer unprecedented precision for calibrating astronomical spectrographs, and have been demonstrated on-sky across bandwidths up to 150 nm (visible) [2] and 400 nm (near-infrared) [3]. Here we demonstrate practical calibration of on-sky spectrograph data from the 10-m Southern African Large Telescope (SALT) telescope using a 15-GHz to 25-GHz comb with an instantaneous visible coverage from 555-890 nm. This broad spectral bandwidth makes it possible to completely calibrate the diffraction orders of the red channel of SALT's R = 65, 000 Échelle spectrograph.