​Engineers from the Group for Advanced Receiver Development at Onsala Space Observatory and Chalmers examine the top part of SEPIA before installation at APEX. On the left Mathias Fredrixon and Denis Meledin (leaning down), and behind them Igor Lapkin. 
S. Krause (Dept. of Earth and Space Sciences, Chalmers)

Desert telescopes ready to discover water in space

​Two of the world’s highest and most advanced telescopes have started searching for water in space – and other surprises – with new eyes. New capabilities for the ALMA and APEX telescopes in Chile’s Atacama desert have been achieved thanks to advanced technology developed by Onsala Space Observatory and Chalmers.

At 5000 metres above sea level, the Chajnantor plateau in northern Chile is one of few places in the world where the air is dry enough to see traces of water in space. Light with a particular colour, specifically with wavelength between 1.4 and 1.9 mm (frequencies between 158 and 211 GHz) is normally blocked by water vapour in the atmosphere. 

From Chajnantor, detecting signs of water in space possible if you have excellent weather conditions – and the right equipment. Since early 2015, the giant telescope ALMA and its neighbour APEX, both located here, have for the first time been able to observe signals from space in these exciting new colours. These wavelengths are sometimes referred to as light, sometimes as radio waves, sometimes simply as millimetre waves. ALMA stands for Atacama Large Millimetre/Submillimetre Array and APEX for Atacama Pathfinder EXperiment.

This opportunity has been made possible thanks to new instrumentation developed by the scientists and engineers in the Group for Advanced Receiver Development (GARD) at Onsala Space Observatory and the Department of Earth and Space Science, Chalmers.

During 2015, new receivers – instruments for detecting and measuring radio waves - underwent their first field tests on ALMA. At the same time on APEX, a receiver with similar design has been tested as part of a new instrument – called SEPIA.

ALMA, an array of 66 antennas, 12 and 7 metres in diameter, which gives astronomers the world’s sharpest views of the universe in light with wavelength around one millimetre, much redder than our eyes can see. ALMA’s much smaller cousin APEX, with its single 12-metre antenna, is not as sharp-sighted, but complements its neighbour thanks to its ability to quickly make deep, sensitive observations of large areas of the sky.

The new instrument SEPIA has been mounted on APEX since early in 2015. SEPIA stands for “Swedish ESO PI receiver for APEX”, but SEPIA is also a colour with a close connection to water. We have cuttlefish of genus SEPIA to thank for the reddish-brown shade which has been used in ink since ancient times.

Advanced tech inside

For astronomers who want to know what the sky looks like at wavelengths as long as 1.4-1.9 mm, advanced technology is as important as dry conditions and big antennas. 

In the heart of the receiver, some of the most remarkable phenomena in physics are used to register and measure faint signals from space. For this the detector needs to be cooled to extremely low temperatures. 

The scientists and engineers at GARD are one of the few radio astronomy instrumentation groups with the facilities and experience that’s needed to meet the challenging requirements of the world’s most advanced telescopes.

– For us, building state-of-the-art instrumentation for telescopes like APEX and ALMA means combining different technologies in the best possible way. The challenge of solving problems in many different fields – for example microwave and millimetre-wave semiconductor and superconductor electronics, microfabrication, physical optics and cryogenics – is what makes this work exciting, says GARD scientist Alexey Pavolotsky.

First signs of water

During 2015, the receivers have been tested for the first time at APEX – as part of SEPIA – and at the antennas of ALMA. 

The results of SEPIA’s first observations – many of them suggested by astronomers in Sweden - are being analysed now.  

For astronomers in Sweden and in the rest of the world, finding and measuring water in space is a major goal. Water’s role in life on Earth makes it an essential part of understanding our cosmic origins, but water molecules in space – for example in clouds in our galaxy where new stars are formed, and around stars that are shedding their outer layers at the end of a long and productive life – have other stories to tell.

Elvire De Beck, astronomer at Chalmers and Onsala Space Observatory, was one of the first to use SEPIA to see signs of water. Together with her colleagues Wouter Vlemmings (also Chalmers and Onsala Space Observatory) and Liz Humphreys (ESO) she collected measurements of the star W Hydrae (see image), an old, red giant star 300 light years away in the constellation Hydra, the Water Snake. The measurements show a strong signal at frequency 183 GHz (1.6 millimetre wavelength), a clear signal of water vapour in dense clouds close to the star.

– SEPIA is working really well. These data show how clearly we can detect water and other molecules around stars like this one. With SEPIA – and soon also in sharper detail with ALMA – measurements like these will be able to tell us a lot about red giants, and that tells us what happens to stars like the Sun when they grow old, Elvire De Beck explains.

Finding water is only part of the story. Other scientists, again many from Sweden, plan to use SEPIA to detect the signatures of other molecules, atoms and ions from both nearby stars and distant galaxies. 

With SEPIA in operation and ALMA’s Band 5 receivers being installed, two of the world’s best telescopes are showing their ability both to study water in space - and to make other discoveries in this new window on the universe. 

While tests continue into late 2015 at both APEX and ALMA, scientists from all over the world can now propose observations with SEPIA, ready for further investigation with ALMA later in 2016. 


More about the project

Receivers for ALMA Band 5 and SEPIA were originally designed and prototyped by the Group for Advanced Receiver Development (GARD) at Onsala Space Observatory and Chalmers University of Technology in Sweden, in collaboration with the Rutherford Appleton Laboratory, UK, and ESO, under the European Commission supported Framework Programme FP6 (ALMA Enhancement). After having successfully tested the prototypes, the first production-type receivers were built and delivered to ALMA in the first half of 2015 by a consortium of NOVA, the Netherlands Research School in Astronomy, and GARD. The room temperature electronics and local oscillator source was delivered by NRAO. By November 2015, 12 receivers have been delivered to ALMA, the first two of which were used for the first test observations in in mid-2015. By 2017, the remainder of the 73 receivers, including spares, will be delivered. 

Further reading





Robert Cumming, astronomer and communications officer, Onsala Space Observatory, +46 31 772 5500, +46 70 49 33 114, robert.cumming@chalmers.se
John Conway, director, Onsala Space Observatory, +46 31 772 5500, john.conway@chalmers.se
Victor Belitsky, professor of radio and space science, Chalmers, leader for Group for Advanced Receiver Development (GARD)  at Onsala Space Observatory and Chalmers, +46 31-772 1893, victor.belitsky@chalmers.se



1. SEPIA is lifted into the telescope. On a snowy day in February 2015, SEPIA is lifted up and into the APEX instrument cabin, 5000 metres up on the Chajnantor plateau in Chile. 
Credit: A. Ermakov (Dept. of Earth and Space Sciences, Chalmers)

2. Advanced components in the heart of the receivers for SEPIA and for ALMA’s Band 5. When cooled to four degrees above absolute zero, the components in this photograph use quantum effects and a niobium superconducting tunnel junction to convert the faint signal from the telescope to data that can be analysed by astronomers. 
Credit: Onsala Space Observatory/E. Sundin

3. Signs of water around the star W Hydrae. Thanks to its new instrument SEPIA, the APEX telescope can now see light with wavelength around 1.5 mm – ideal for measuring signs of water in space. Among the first targets is the red giant star W Hydrae, around 300 light years from Earth. This spectrum from SEPIA shows clear signals of warm water vapour close to the star. With these measurements, and follow-up observations with ALMA, scientists will try to understand how red giant stars contribute to the cosmic ecosystem. 
Credit: ESA/Herschel/MESS (Mass-loss of Evolved StarS) program/N. Cox & F. Kerschbaum (background); W. Vlemmings, E. De Beck and E. Humphreys (spectrum)

4. A receiver cartridge for 1.4-1.9 mm (Band 5). Engineer Mathias Fredrixon, GARD, working on one of the first receivers made for the ALMA Band 5 project – now upgraded and part of the new instrument SEPIA on APEX. 
Credit: Onsala Space Observatory/A. Pavolotsky



Page manager Published: Wed 04 Nov 2015.