On March 18, 2012, an interferometer test was conducted at the Array Operations Site (AOS) at 5000 m asl using two Japanese 7-m antennas equipped with the Band 8 receiver manufactured by NAOJ, and interference fringes were successfully obtained.

On the following day, another interferometer test was carried out and fringes of the emission of carbon monoxide molecule at 461 GHz around R Aquilae were successfully detected. The figures below show the spectrum (right) and phase (left) obtained in this interferometer test. The slightly protruding red lines in the left figure indicate the radio waves emitted by carbon monoxide molecule. In the phase diagram (right), you can see signals (red dots) concentrated around the center within the same frequency range at around the channel number 3000 to 4000 on the horizontal axis as shown in the spectral graph (left). These results demonstrate that signals received by the two antennas are properly cross-correlated and the two antennas are working well as an interferometer. In observations with a radio telescope like ALMA, we check the observation results with spectral graphs like these unlike optical observations where we can see the image just after the observation.

The picture below shows Héctor Alarcón (deputy leader of the Telescope Operator Group at the Joint ALMA Observatory (JAO)) indicating the spectral graph of the successful interferometer test and Shin’ichiro Asayama (assistant professor at the NAOJ and senior RF engineer at the JAO).

[Photographed by Paulo Cortes]