Interview with Giovanni Cresci (Inaf) on the new instrument just approved by Eso for the Vlt, Mavis. It will cost about 12 million euros (8 already funded), will make adaptive optics in the visible and will allow the telescope to reach the sensitivity and resolution of the next generation giant telescopes, remaining at the forefront of astronomical research.
With the signing of the agreement with Ex (announced today , Tuesday, June 1), the project Mavis – a new innovative tool designed for the VLT – enters the so-called Phase B . The design of the instrument then begins in view of the next stage, the Preliminary Design Review . What characteristics must an instrument have to be considered worthy of being included in a system that – between the individual Vlt telescopes and the Vlti network – already boasts at least fifteen others? Media Inaf went to ask Giovanni Cresci , co-project scientist of Mavis and researcher of INAF of Arcetri.
With the start of Phase B , it starts to get serious. However, there are still many steps to be taken. What are the timelines?
«I would say that the most important date to keep in mind is when the instrument will have to be operational at the telescope: this is what interests astronomers and also those who want to see the results in terms of the instrument’s performance. We are talking about 2028, date in line – among other things – with the implementation of the first instruments of the Extremely large telescope ( Elt ), the 30-meter ESO telescope that will soon be built in Chile ».
Why does he emphasize this alignment?
«It is an interesting combination because on the one hand we will have Mavis, which will obtain images with very high angular resolution in the visible, and on the other Elt, which will reach the same resolution in the infrared. A unique synergy can be established between the two ».
About seven years to go from concept to realization. Is it likely as a time frame?
«Our schedule foresees that it is, even if unexpected events and delays can always happen. Until now, however, despite the pandemic – which has greatly limited the possibility of interaction and work in the laboratories – we have managed to stay on time and conclude Phase A with excellent results. The Mavis consortium is mainly composed of some INAF offices in Italy and various Australian institutes, plus a contribution from the Laboratoire d’Astrophysique de Marseille (Lam): we work with time differences of ten hours and the fact of not being able to see each other in person he weighed a lot ».
Before looking closely at the division of roles between partners, however, let’s take a step back. What is Mavis?
“Mavis is an instrument that will make multi-conjugated adaptive optics in the visible: it will use 8 laser guide stars and 3 natural guide stars to make a correction of the turbulence introduced by the Earth’s atmosphere on a very large field of 30 × 30 arc seconds – rather than correcting a very small field of view as the tools available today do. Moreover, it will do so at optical wavelengths ».
Which is totally new, right?
“Exact. A few years ago we began to do adaptive optics also to optical wavelengths but limiting ourselves to a small source in the center of the field, while this instrument will allow to do so on a large field. Mavis will allow its imager to obtain images at a resolution three times better than that of the Hubble Space Telescope. In addition, it is also equipped with an integral field spectrograph, which will provide a spectrum with a resolution of approximately 20 milliarcoseconds for each point of a field of 6 × 6 arc seconds. It is a revolutionary instrument which, thanks to its angular resolution and sensitivity, will allow us to do astronomy as we have never done so far ».
Will the full-field spectrograph be better than Muse ?
“It will be different and somewhat complementary to Muse – which is a spectrograph that covers a very large field, 1 × 1 arc minutes. With Mavis we will be able to study the regions at the center of galaxies or globular clusters where the sources have a very high density and cannot be solved individually with Muse ».
What other adaptive optics tools are currently present at the Vlt?
«The adaptive tools in the visible are Sphere and Muse, and they have two main limitations: they work on very small fields and they need a very bright star to guide the adaptive optics system. Mavis will overcome these limits, and will be able to see about an order of magnitude more sources than those currently observable in the visible. For example, at the Galactic Pole , where there are fewer stars, Muse can only see 5 percent of the sources. With Mavis, on the other hand, we will be able to reach 50 percent ».
What are the main risks and the main technological challenges in making Mavis?
«As I said before, this is the first time that multi-conjugated adaptive optics have been done in the visible – usually in infrared. This is our great technological challenge. However, we think that the techniques developed up to now in the infrared are mature enough to allow such an extension. It is difficult, but we can also count on what the Vlt already offers us ».
“The idea is to use an infrastructure already present in one of the four telescopes, which has a deformable secondary mirror with 1170 actuators and four laser guide stars working for Muse.”
The four stars, however, are not enough, according to what he told me before.
“No, we need eight stars. Our solution is to divide the laser beam of each one in two: instead of having four lasers we will have eight with a reduced power ».
How much money has been allocated for this tool?
“Thus, the workforce is provided by the partners, who will receive approximately 150 nights of guaranteed observation time. Inaf will therefore have about 45 percent of these nights. As for the hardware, Eso will finance us with eight million euros, which however are not enough to complete the tool. We need about 10 million plus two in contingency – for the unexpected. We are working to find the missing sum ».
How do you plan to do?
«First of all, by participating in European and Australian calls for funding and grants , or by identifying a new partner who wants to join the consortium by bringing the money that is missing to be able to implement the instrument. We think we can do it quickly, given that we already have the bulk of the sum ».
What led to the signing of this agreement today?
«We had to pass a first review at the end of the so-called Phase A , in which Eso verified that the design of the instrument met the needs that the institution had for it. Before signing, we also had to negotiate the technical and scientific requirements of Mavis to make explicit the objectives to be achieved ».
How will the work be divided between the partners?
“Most of the effort is shared between INAF and a consortium of Australian institutes. As for Inaf, we will mainly deal with adaptive optics and instrument software, while the Australians will focus on wavefront sensors for lasers and postfocal instrumentation: imager and spectrograph. Lam instead will mainly deal with the postprocessing of raw data, in particular with the reconstruction of the point spread function . Finally, there is Eso, who will take care of inserting the instrument into the telescope and interfacing with the other instruments ».
All these parts, therefore, will be developed separately. In which laboratory will the integration take place?
“In Australia, at the Stromlo Observatory . And finally in Chile for integration with the telescope ».
In Italy, however, in which laboratories will you work?
«In the laboratories of the Inaf headquarters in Padua».
If you were to identify an emblematic scientific case to which Mavis will contribute, what would you say?
«So, it is a bit difficult, because this instrument will deal with numerous and very different scientific cases: from the Solar System to the most distant galaxies. Kind of like Hubble did , and in fact Mavis sets out to be a bit of Hubble’s replacement when it can’t work anymore. However, I can mention something particularly interesting: First, we want to create the deepest image ever made of the universe. With 10 hours of integration it will be possible to observe galaxies even fainter than those seen in the Hubble Ultra Deep Field, the deepest picture of the universe we have so far. It will also be possible to investigate the origin of supermassive black holes, whose primordial seeds should reside at the center of low-mass objects such as globular clusters or dwarf galaxies. Before Mavis, we did not have the angular resolution necessary to do astrometry at this level of precision ».
So, if everything goes as it should, will Mavis have nothing to envy to a space telescope like Hubble despite being on Earth?
“Exactly. In fact, it should be more sensitive and be able to see finer details. In fact, with this adaptive optics system, the damaging effect of the Earth’s atmosphere should be overcome. But, above all, it will be interesting that Mavis will be the optical counterpart of what we will do in the infrared with the great telescopes of the future like Elt ».
As if to say that it will give a new life to Vlt allowing it to stay on track alongside the telescopes of the future.
What is your role in Mavis?
«As regards the scientific part, we have two project scientists : one for the Australian part and one for Inaf, which is me. I am mainly concerned with ensuring that the characteristics of the instrument are the optimal ones for doing the science that is required. For the scientific part, then, there is also a representative for each site that participates in the construction of the instrument. In the case of Inaf, therefore, the offices of Arcetri, Rome and Padua. In identifying scientific cases for Mavis, Italy played the lion’s share: when there was a call from Eso for the presentation of scientific proposals, more than half of the proposed projects had Italian principal investigators ».
Besides being involved in many projects of telescope instruments, you use them to do science. What do you do?
«I deal with the evolution of galaxies – especially chemical evolution – from the local universe to the more distant one. I am also involved in the co-evolution between the central black hole and the host galaxy. Also for the scientific progress of these two areas Mavis will be a revolutionary tool. As he said, I also deal a lot with instrumentation: I think it is interesting for us scientists to understand what is the whole process that is needed to build and optimize the instruments, and allow them to obtain the results we are looking for from them ».
Does knowing the tools in depth also allow us to think about more adequate scientific cases?
“Of course. And also to better understand what problems can arise in the data and how to solve any oddities or artifacts that can only be understood by knowing the instrument in depth ».
Featured image: Rendering of the Mavis tool. Credits: Eso / Mavis consortium / L. Calçada
Provided by INAF