A full description of HERA HEterodyne Receiver Array and its observing modes is given in the HERA manual. Here we only give a short summary.
The 9 dual-polarization pixels are arranged in the form of a center-filled square and are separated by . Each beam is split into two linear polarizations which couple to separate SIS mixers. The 18 mixers feed 18 independent IF chains. Each set of 9 mixers is pumped by a separate local oscillator system. The same positions can thus be observed simultaneously at any two frequencies inside the HERA tuning range (210-276 GHz for the first polarization, and 210-242 for the second polarization).
A derotator optical assembly can be set to keep the 9 pixel pattern stationary in the equatorial or horizontal coordinates. Receiver characteristics are listed in Tab. .
Recent observations have shown that the noise temperature of the pixels of the second polarization array may vary across the 1 GHz IF band. The highest noise occurs towards the band edges which are, unfortunately, picked up when HERA is connected with VESPA whose narrow observing band is located close to the lower edge of the 1 GHz band. Therefore, while not as important for wide band observations with centered IF band, the system noise in narrow mode is higher (factor 1.5 - 2) as compared to the first polarization array. We do not recommend to use the second polarization for frequencies GHz.
HERA can be connected to three sets of backends:
HERA is operational in two basic spectroscopic observing modes: (i) raster maps3 of areas typically not smaller than , in position, wobbler, or frequency switching modes, and (ii) on-the-fly maps of moderate size (typically ). Extragalactic proposals should take into account the current limitations of OTF line maps, as described in the HERA User Manual, due to baseline instabilities induced by residual calibration errors. HERA proposers should use the web-based Time Estimator. For details about observing with HERA, consult the User manual. The HERA project scientist, Karl Schuster (schuster@iram.fr), or Albrecht Sievers (sievers@iram.es), the astronomer in charge of HERA, may also be contacted.
Accepted HERA proposals will be pooled together in order to make more efficient use of stable 1.3mm observing conditions (see section . Questions concerning the HERA pool organization can be directed to the scheduler (thum@iram.fr) or the HERA Pool Coordinator, Helmut Wiesemeyer (wiesemeyer@iram.es).