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Spectrum's digitizer cards used by Max Planck Institute to measure diameters of distant stars | Spectrum

World's largest Cherenkov telescopes get their enormous sensivity with the help of Spectrum digitizers
The MAGIC telescopes on the Canary Island of La Palma were built to observe cosmic objects that emit high-energy gamma rays, i.e. supernovae or black holes. Astronomers also use the twin telescope to measure the diameter of stars to investigate the processes throughout their life cycle. This is a challenging task for earthbound telescopes, since the angular diameter of stars is extremely small: only a few milli-arc-seconds. That is about the size of a coin on top of the Eiffel Tower as seen from New York! Not even the largest telescopes in the world are able to measure them directly. Instead, the researchers record the light intensity of an object by combining the light from several telescopes at a distance of tens of meters – a technique called intensity interferometry. However, the signals are very weak so any spurious signals and crosstalk would swamp them. Having evaluated several makes of digitizer card, Spectrum Instrumentation M4i.4450-x8 digitizer cards were selected.
MAGIC (Major Atmospheric Gamma-Ray Imaging Cherenkov) are the world's largest air-Cherenkov-telescopes each with a diameter of 17m.

"We found that these cards not only had the lowest levels of spurious signals and crosstalk of all the PC cards that we tested," said David Fink from the Max Planck Institute for Physics, who is in charge of Electronic Development on the project, "but the performance of each card was also identical. The latter is so important as you are trying to compare the differences between the signals from each telescope. The technique is very sensitive to correlated signals and crosstalk between channels including anything picked up along the way from the optical sensors through to the computer that the digitizer cards are mounted in. To put it into perspective, these Spectrum cards enable us to precisely measure fluctuations of the light intensity on nanosecond time scales giving unprecedented sensitivity that is around ten times better than that achieved in the 1970s with the Narrabri interferometer."

"The other important factor in choosing Spectrum digitizer cards is their excellent reputation for reliability. The cards are located by the two telescopes that are high up in the mountains on the island of La Palma, one of Spain's Canary Islands, so it is not a simple matter to swap in a new card if there is an issue. Plus, there is the cost of instrument downtime and lost observation time. The fact that Spectrum provides a five-year warranty shows their faith in the high quality and reliability of their cards which was supported when we checked with other users in the scientific community. Lastly, Spectrum assured us that they can repair cards long after the five years have passed. That i very reassuring as long-term experiments can often be confronted with a large effort to redevelop a system because the original hardware at the heart of it is no longer available."

The telescopes in the north of the island are currently not threatened by the volcanic eruption, as the volcano is located in the south of La Palma.

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Photos courtesy of MAGIC Collaboration, photo 1 by Giovanni Ceribella and photo 2 by Robert Wagner.