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The New GREAT SOFIA Scenario With 4GREAT
Wednesday, February 21, 2018 - 9:00am PST
Carlos A. Durán
The German REceiver for Astronomy at Terahertz frequencies has been successfully in service onboard SOFIA since 2011. GREAT, with its modular approach, is composed of a group of cryostats containing detectors for different frequency bands between 1.25 and 4.7 THz. Individual cryostats are then grouped in pairs. 4GREAT, a new member of the GREAT constellation, is a four-color single-pixel- detector. Two channels, CH1 and CH2, are implemented using spare flight mixers of Herschel-Heterodyne Instrument for the Far-Infrared: HIFI band 1 (492– 635 GHz) and band 4 (892-1100 GHz). The third channel -CH3- makes use of the GREAT L1 detector (1.2 – 1.5 THz), while the fourth –CH4- covers the entire frequency range of GREAT Ma,b (2.5-2.7 THz), using a variation of one the upGREAT HFA mixers. The channels are all co-aligned on sky in a single closed-cycle cooled cryostat. 3 Channels of 4G have been commissioned by July-2017, while the fourth one has been recently integrated, making the system ready for the next observing campaign. It will be used simultaneously with the upGREAT-HFA (an array of 7 pixels at 4.745 THz covering the line of atomic oxygen [O I]), allowing multiple frequency band observations of astrophysically important transitions including ammonia (NH3), the methylidyne radical (CH), ground-state isotopic water H218O, hydroxyl (OH), and carbon monoxide among many others.