Lillo Box, J., Aceituno, J., Pedraz, S., Bergond, G., Galadi Enríquez, D., Azzaro, M., Arroyo Torres, B., Fernández Martín, A., Guijarro, A., Hedrosa, R. P., Hemelo, I., Hoyo, F., Martín Fernández, P. (2020). CAFE(2): an upgrade to the CAFE high-resolution spectrograph. Commissioning results and new public pipeline. Monthly Notices of teh Royal Astronomical Society 491, 3, 4496-4508 DOI: 10.1093/mnras/stz3283
CAFE is a high-resolution spectrograph with high-precision radial velocity capabilities mounted at the 2.2 m telescope of Calar Alto Observatory. It suffered from strong degradation after 4 yr of operations and it has now been upgraded. The upgrades of the instrument (now named CAFE(2)) aimed at recovering the throughput and improving the stability due to the installation of a new grating, an active temperature control in the isolated coude room, and a new scrambling system. In this paper, we present the results of the new commissioning of the instrument and a new pipeline (CAFExtractor) that provides the user with fully reduced data including radial velocity measurements of FGK dwarf stars. The commissioning results show a clear improvement in the instrument performance. The room temperature is now stabilized down to 5 mK during one night and below 50 mK over two months. CAFE2 now provides 3 m s(-1) precision on the reference ThAr frames and the on-sky tests provide a radial velocity precision of 8 m s(-1) during one night (for S/N > 50). The throughput of the instrument is now back to nominal values with an efficiency of around 15 per cent at 550 nm. The limiting magnitude of the instrument for a 1 h exposure and S/N = 20 is V = 15. With all these properties, CAFE enters into the small family of high-resolution spectrographs at 2-4 m telescopes capable of reaching radial velocity precisions below 10 m s(-1).
