The BlackGEM array (Conference Presentation)

The BlackGEM Phase 1 array for optical synoptic surveys consists of three wide-field telescopes providing an 8.1 square degrees field-of-view sampled at 0.56". It will be installed at the ESO La Silla Observatory. Each unit telescope consists of a modified Dall-Kirkham (Wynne-Harmer) configuration with a 65cm parabolic primary mirror, a 23cm spherical secondary and a triplet corrector lens. The third lens in the triplet is motorized to double as an Atmospheric Dispersion Corrector. The 10cm x 10cm flat, achromatic focal plane contains a single STA1600 10.5k x 10.5k chip with 9 micron pixels, providing a 2.7 square degree field-of-view sampled at 0.56"/pix. The telescope is equipped with a 6 slot (u,g,q,r,i,z) filter wheel. Limiting magnitude (5 sigma) in dark conditions is q=23 in 300s integration in 1" seeing. The telescope structure is made from carbon-fibre for maximum stability. The secondary mirror is mounted on a piezo-stage for active control. Each telescope is mounted on the Fornax 200 mount. On La Silla each telescope will be housed in a clamshell dome, and be located on a 7m high double-walled cylinder to lift it above the ground-layer seeing. The outer cylinder will carry the dome and the inner cylinder the telescope. The scientific program of BlackGEM is centered on optical afterglows of gravitational wave mergers, reacting to Advanced LIGO/Virgo triggers. The array will also perform a full southern sky survey (BG-SASS), covering 30000 square degrees (Dec < +30d) down to 22nd magnitude in all six filters at 1" resolution; a fast synoptic survey at 1 minute cadence for characterization of fast transients; bi-weekly all-sky q-band scan; and a twilight survey of the local universe. The BlackGEM consortium consists of the Netherlands Research School for Astronomy (NOVA), Radboud University and KU Leuven as founding members and the University of Manchester, UC Davis, Tel Aviv University, the Weizmann Institute, the University of Canterbury and the Hebrew University Jerusalem as partners. BlackGEM data will be processed on-line for transients and a full-source database using optimal photometry and the ZOGY image subtraction techniques. BlackGEM transients will be announced publically upon detection. All BlackGEM data will be cloud-based, including the 150Tb live database of the full source photometry. BlackGEM Phase 1 is scheduled for installation on La Silla in Q2-Q3 2018 and start of operations of in Q4 2018. In Phase 2 (2019-2022) the array is to be expanded to 15 unit telescopes, providing a 40.5 square degree instantaneous field-of-view. An overview of the array, first results of the prototype and an update of the installation will be given. www.blackgem.org