Successful Interferometer Test with Japanese Band 10 Receiver—Birth of Highest Frequency Radio Interferometer

On October 26 (Chilean Time), the Joint ALMA Observatory (JAO) successfully detected interference fringes from Callisto (a satellite of Jupiter) and Orion KL at 863 GHz and 806 GHz respectively in an interferometer test with two Band 10 receivers developed by the National Astronomical Observatory of Japan (NAOJ). This is the highest frequency ever achieved by an interferometer.

Figure. Spectrum and phase of Orion KL

Figure. Spectrum and phase of Orion KL
Click to Enlarge (PNG/ 116KB)

This figure shows the spectrum (top) and the phase (bottom) of the emission from carbon monoxide molecule of Orion KL obtained in this test observation. Orion KL is known to contain an active star forming region. The spectrum of complicated shapes indicates that dynamic gas activity is taking place, while the phase shows possible gas outburst in Orion KL.

This test observation was conducted at the ALMA Array Operations Site (at 5000 m asl.) with two Japanese 7-m antennas, each of which is equipped with a Band 10 receiver. Received signals were processed by the ACA correlators developed by Japan. This high frequency observation was made possible by the combination of ideal atmospheric condition (dryness) of the Atacama Desert, high surface accuracy of the antenna, and proper functions of all components as an entire array system including the Band 10 receiver.

To cover a wide range of observing frequencies, each of the ALMA antennas is equipped with ten types of receivers dedicated to different frequency bands. The development of the Band 10 receiver for the highest frequency band (787 GHz to 950 GHz) was extremely difficult and faced many technical challenges from its material selection. Since the Band 10 specifications couldn’t be satisfied by the existing superconducting material used for the other frequency bands, a new superconducting material was developed by the development team at the NAOJ Advanced Technology Center to realize the state-of-the-art ALMA receiver.

The picture shows the ALMA staff celebrating the success of the test at the control room in the Operations Support Facility (2900 m asl).