Comet 67P observations with LOTUS: a new near-UV spectrograph for the Liverpool Telescope

The European Space Agency’s Rosetta spacecraft has been orbiting comet 67P/Churyumov-Gerasimenko (hereinafter “67P”) since August 2014, providing in-situ measurements of the dust, gas and plasma content of the coma within ~100km of the nucleus. Supporting the mission is a world-wide coordinated campaign of simultaneous ground-based observations of 67P (www.rosetta-campaign.net), providing wider context of the outer coma and tail invisible to Rosetta. We can now compare these observations, augmented by "ground truth" from Rosetta, with those of other comets past and future that are only observed from Earth.The robotic Liverpool Telescope (LT) is part of this campaign due to its unique ability to flexibly and autonomously schedule regular observations over entire semesters. Its optical imagery has recently been supplemented by near-UV spectroscopy to observe the UV molecular bands below 4000Å that are of considerable interest to cometary science. The LT's existing spectrographs FRODOSpec and SPRAT cut off at 4000Å, so the Liverpool Telescope Optical-to-UV Spectrograph - LOTUS - was fast-track designed, built and deployed on-sky in just five months. LOTUS contains no moving parts; acquisition is made with the LT's IO:O imaging camera, and different width slits for calibration and science are selected by fine-tuning the telescope's pointing on an innovative "step" design in its single slit.We present here details of the LOTUS spectrograph, and some preliminary results of our ongoing observations of comet 67P.