Blinking flash in the dark

Paranal sky has been at its best for our last night of this run: perfectly clear and with enough ground layer to enjoy the power of the AOF. We focused on  performance assessment, looking to star’s cluster at various places and measuring the improved image quality when we turn on and off the adaptive optics system.

We perform many on/off sequence of observations to measure the improvement of image quality brought by the AOF (photo Roland)
Core of the galaxy cluster Abell 2204, showing structured gas emission around the Brightest Cluster Galaxy (near the bottom of the image). A small horizontal arc is also visible above and is due to gravitational lensing (image Johan R)

We also took some longer exposure to measure the laser background impact.


A first quick analysis of the system performances gives us confidence that we will achieve a significant improvement of image quality most of the time. This will open a new discovery space for MUSE.

Thanks to AOF and Paranal experts, the robustness of the system has been much improved during this first commissioning. There is nevertheless still a number of open actions and we will be back in two weeks for another commissioning run.

The AOF magician Johann is invoking the laser power (photo Roland).

It is time for us to leave. Thanks to all of you – Elena, Fernando, Gérard,  Joel, Johan, Johann,  Pierre, Peter,  Ralf, Sebastian – for all the work performed in a very nice and constructive atmosphere. The commissioning team is tiny part of a group of many talented people which have been working hard for many years to achieve this fantastic results, the list is too long to be written here, but I want to warmly thank all of you. Thanks also to the Paranal staff for its hospitality and support.

It has been a great experience to share and we enjoyed so much the laser show in the magnificent sky of Paranal.

Laser traffic upon UT2 (photo Peter).

Stay tuned, we will be back on July 13th.




A perfect night


Sunset at Paranal, the start of a perfect night (photo Roland)

At sunset, Paranal sky shows its intention to cooperate, and indeed, it did all night. After a look at the beautiful sunset, we did not even wait for the sky to be fully dark and could start the big laser show.

The laser is of course the most obvious part you see when you are on the platform. But it is only a subset of the AOF, a fantastic master piece of technology.

A typical observation always start by pointing the telescope to the target and then shaping the primary mirror to the correct optical surface to produce sharp images (the so-called active optics system). Then the laser show starts. First the beam is propagated and hits the atmospheric sodium layer at 90 km above, producing four artificial stars. The four wave-front sensor cameras are then pointed to the laser guide stars. The field selector is then moved to the selected natural tip/tilt guide star and locked to it. The full analysis of the atmospheric turbulence is then performed using these 5 guide stars. Information is processed in real time, 500 times by second, and the computed correction is sent to the secondary deformable mirror. This mirror of 1 m diameter and only 2 mm thickness, is levitating, linked to its support only by active magnets. The deformation of the mirror then corrects the light entering MUSE, producing even sharper images.

The closing of the numerous loops to control this complex system is performed in 2 min. Impressive. And then you can monitor the system on the numerous screens.

AOF GALACSI monitoring screen displays in real time the shape of the deformable secondary mirror (lower right), the tip/tilt star (lower left) and the four laser wave front sensors (upper-left panels). Video Roland.

After performance measurements on a globular cluster, we went to some deep sky exposures to evaluate the impact of the lasers on the background. There is no moon, time to go to the platform and contemplate the millions of stars of the Paranal sky. These four bright light sabers pointing to the target add a surrealistic touch to this fascinating landscape.

Laser shot pointing to M68 seen from the UT4 dome (photo Roland)
Reconstructed color image of a short exposure (1 sec) of Saturn (image Peter).

This night was very productive, we obtained many gigabytes of excellent data over various targets. In the middle of the night, we even did a stop to greet the lord of the rings.

At six in the morning, after this successful long night, it is time to take some rest before the next one.

Cloudy outside, bubbles inside


Cloudy night at Paranal (photo Peter)

Many clouds and gray sky at the start of the night did not look very promising. We nevertheless launch the laser and close the loop on some bright tit/tilt star to perform further tests. We also continue to investigate software issues.

Celebrating first light (photo Diego)
Chair crisis in the VLTI control room (photo Roland)

But Paranal sky did not want to cooperate and remained cloudy all night. Although the show of the lasers shining through the various layers of clouds was nice, we took this opportunity of free time to pop a few champagne
corks to celebrate the first adapted light of MUSE. Suddenly the grumpy atmosphere became much more cheerful. Many

The question is “why is the field selector at this location” (photo Roland)

thanks to the Paranal chef and his staff for the delicious petit fours and mini cakes.

The rest of the night was spent on functional tests, software debugging and long discussions  about the GALACSI field selector, the elongation of stars and various others items.

Deep thinking about center of rotations, offsets and directions. Joel knows the solution (photo Roland)

Let’s hope for a clear night tomorrow.

How is your ground layer today ?

“Did you get good seeing last night ? Excellent at the start,  but at the end very poor ? I wish you clear sky and good seeing for this night …”

Nice sunset, no wind, time to go ! (photo Roland)

This is the typical discussion you can hear at any ground based observatory site because seeing is the obsession of all observers. However if you want to be trendy, you have to ask about ground layer. Nowadays  if you happen to meet some MUSE observers you may hear something like this: “did you say 80% of ground layer ? that’s great, let’s go to the next target then”.

The great laser show over the milky way (Photo Roland)

The ground layer is the part of turbulence layer (the first 500 m) which is beautifully corrected by the AOF GALACSI Ground-Layer mode, just before entering MUSE. And if it happens that most of the turbulence is in this layer, then the improvement of the image quality shall be good. That was indeed the idea 15 years ago when discussing the AOF project and its coupling with MUSE.

Photo Johan R

This second night looks favourable. The wind stopped and a few clouds stay a bit at sunset, just the time to take some nice pictures. Soon after dark time, the laser show start. Tonight’s show was quite spectacular, it is an unforgettable experience to stand over the platform looking at the milky way spiked by four blazing swords.

Back to the control room, while some are performing additional tests to find solutions of the few issues identified at the first night, others are producing the first analysis of the performance tests, on the globular clusters NGC5694 and M75.  In both cases we can see the two direct gains of the AO: the many stars in the cluster get sharper images, and some of the faintest stars in the fields reveal themselves much more easily.

A stellar field in the vicinity of the globular cluster NGC5694, with and without the adaptive optics correction (Image Roland)








The center of the globular cluster M75 in open and closed loop (Image Johan R).
Planetary nebula IC4406 (in Lupus) 2000 light years away (Image Johan R)

Overall, it was a very good night. We obtained data of excellent quality and learned a lot about the system.

Welcome back

Joel and Johann K are inspecting the GALACSI AOF module in the integration hall at ESO Garching (photo Roland)

Three years after the end of MUSE commissioning, we are back to Paranal for another exciting adventure, the coupling of the Adaptive Optics Facility with MUSE.

But what happened during these three years ?  After its very successful commissioning, MUSE was immediately offered to the community and it became so popular that it is currently one of the most demanded instrument of all VLT instrument suite. It has since produced many discoveries, published in scientific journals and some of them have been reported in ESO Press Releases.

Cloudy sunset, high winds at the start of the night (photo Roland)

In parallel, ESO engineers have been working hard to transform UT4 in an adaptive optics telescope. The so called Adaptive Optics Facility (AOF) and its GALACSI module, will correct for the blur produced by the atmosphere, producing sharp images that will boost MUSE performances.

Kick-off meeting at the Residencia to prepare the night program (photo Roland).

The coupling of these two complex systems, AOF and MUSE, will produce one of the most advanced and powerful technological system ever built for ground based Astronomy. Improved spatial resolution, i.e sharper images, will not only allow MUSE to scrutinize in even more detail objects in the sky but will also improve its detection limits to fainter objects.

An experienced team of MUSE observers has joined the talented AOF team and the crew at Paranal for this first commissioning run of 5 nights.  AOF has been independently tested by the AOF team over the past months. Everything is in place, but the commissioning of such a complex system is not straightforward, nobody knows how long it will take to get it ready for science. Expectations are high.

We finally meet the four lasers … very impressive ! (photo Roland)

For our first night with the new system, we planned a battery of tests for the performances “end-to-end”. The idea was to measure the gain offered by the AOF on MUSE for given atmospheric conditions. Despite the strong winds and some small technical issues with the telescope very early in the night, we were soon rewarded by the spectacular images obtained thanks to the

The slow guiding system oscillations show the change of image quality when we switch the AOF on or off (photo Roland)

AO!  Playing with the switch “On / Off” we could clearly measure the gain in image quality.

While the very long winter night is approaching the end, we face a number of technical problems. Debugging such a complex system at 5 am is not the easiest task.

Despite these small mishaps, this first night has already given some interesting results that we have to digest. Robustness has still to be improved but the performances seem very good.

Stay tuned, for some nice images tomorrow.