LOTUS: a low-cost, ultraviolet spectrograph
Marchant, J. M.; Steele, I. A.; Snodgrass, C.; Jehin, E.; Smith, R. J.; Jermak, H. E.; de Val-Borro, M.; Jones, G.; Mottram, C. J.; Fitzsimmons, A.; Barnsley, R. M.; Bates, S. D.; Clay, N. R.
United Kingdom, Belgium, United States
Abstract
We describe the design, construction and commissioning of a simple, low-cost long-slit spectrograph for the Liverpool Telescope. The design is optimized for near-UV and visible wavelengths and uses all transmitting optics. It exploits the instrument focal plane field curvature to partially correct axial chromatic aberration. A stepped slit provides narrow (2.5 × 95 arcsec) and wide (5 × 25 arcsec) options that are optimized for spectral resolution and flux calibration, respectively. On sky testing shows a wavelength range of 3200-6300 Å with a peak system throughput (including detector quantum efficiency) of 15 per cent and wavelength dependent spectral resolution of R = 225-430. By repeated observations of the symbiotic emission line star AG Peg, we demonstrate the wavelength stability of the system is <2 Å rms and is limited by the positioning of the object in the slit. The spectrograph is now in routine operation monitoring the activity of comet 67P/Churyumov-Gerasimenko during its current post-perihelion apparition.