With a little help from our friends: Finding a home for E-ELT March 4, 2010
Posted by sarah in: astronomy, politics , trackback
Cerro Paranal (middle right) and Cerro Armazones (middle left)
ESO announced today that their Council have recommended Cerro Armazones in the Chilean Andes as the preferred site for their next generation optical/IR observatory, the 42-m European Extremely Large Telescope. The decision came in response to the delivery of a technical report by the organisation’s E-ELT Site Selection Advisory Committee, from which Armazones emerged as the frontrunner, “because it has the best balance of sky quality across all aspects and it can be operated in an integrated fashion with the existing ESO Paranal Observatory”.
So does this means the deal is done? Apparently not. The text also tells us that ESO have received proposals to host the telescope from both Spain, who would like to see the telescope site on La Palma, and Chile, so a final run-off between these two countries now seems likely.
What has struck me about this whole site selection exercise is the different approaches taken by ESO for the E-ELT and their North American counterparts, the Thirty Meter Telescope project.
Choosing the site for a new telescope, particularly one which will represent the interests of astronomers in much of Europe, is a hugely complex process – I’ve talked about it before, here. As well as the purely scientific merit of the site for astronomical research, there are a bunch of other considerations: how accessible is a site, where would the astronomers live and work, is there access to a power grid, where is the nearest water source? On top of that there are the diplomatic and political aspects: is the government and scientific community of the host country on board, is the local population open to an invasion of foreign scientists, are there significant business interests in the region? It’s clear that picking a site for the E-ELT is a very involved process that should be handled with sensitivity, diplomacy and a great deal of political nous.
Despite all these considerations that come into play, let’s not forget about the science of site selection. Astronomers’ interest in the skies start with our own local skies, and our weather. In the last century our understanding of the influence of atmospheric conditions on astronomical observations has increased hugely. Temperature, pressure, wind, humidity and other molecular abundances from the ground up to several kilometres in height all have their unique effects on the quality of our data. With the advent of smart telescope technologies that correct in real time for environmental fluctuations, like active and adaptive optics, the need for a detailed knowledge of local conditions both on a spatial and temporal scales becomes ever more important. The huge investment needed for telescopes like the E-ELT demands that we try to get the best possible astronomical site to get the best bang for our buck euros.
Given all that, the committee’s recommendation of Cerro Armazones comes as no surpise. Located close to ESO’s existing facilities at Paranal at a shade over 3000 m in altitude, Armazones appears to be an excellent site. It only became a (presumed) candidate E-ELT site last summer, when the E-ELT’s US counterpart, the Thirty Meter Telescope, announced that their telescope would be built on Mauna Kea in Hawaii. TMT had selected Armazones as one of its frontrunner sites back in 2008, so the Mauna Kea decision freed up the spot for ESO. So in fact, if the E-ELT does go to Armazones, the European community will have benefited massively from the North Americans’ early testing of the site.
And this brings me to the researchy part of this post. I’m loving the way TMT have kept the community informed of their site testing activities. Scientists working for the project have carried out an extensive 5-year campaign at five different sites: Cerro Armazones (Chile, 3064 m) , Mauna Kea (US, 4050 m), Cerro Tolonchar (Chile, 4480 m), Cerro Tolar (Chile, 2290 m) and San Pedro Martir (Mexico, 2830 m). Last year, Schöck et al published the first of a series of 12 (!!) papers in PASP detailing the results of the campaign. This first paper is an excellent read, with a clear overview of the chosen sites and the parameters they studied. More importantly, they talk about the constraints of their work, both in terms of available instruments, calibration and data processing.
As far as I can see, four of the 12 papers have been published so far, dealing with seeing and isoplanatic angle (Skidmore et al, 2009); turbulence profiles (Els et al, 2009); turbulence coherence time (Travouillon et al, 2009). The rest are still in preparation, although much work has been presented at conferences as well (a good listing here). From what I can gather, the TMT site testing team have done a very good job at planning their campaign and gaining the best possible understanding of their equipment and data analysis methods.
In my perhaps limited view, ESO’s reports on site testing have been a bit confusing. Back in 2008, there were five official candidate sites (pdf) – including La Palma but not Armazones. Today’s announcement tells me there were indeed five shortlisted sites, but three of those are different to those on 2008′s list. I’d heard some gossip about there being more sites under consideration, but no names mentioned. It all seemed a little hush-hush, or rather, it was not something the community was being actively updated on. But maybe that just reflects my status as a lowly minion.
The best part of the TMT testing is that the team have created an online database with all their test data from the 5-year survey, free for anyone to download, with a wealth of background and context. I’ve often argued that observatories should treat their site monitoring data the same as the science data, and make them available in archives with proper formatting and metadata.
ESO have tons of astroclimatology data available on their site (see e.g. here, here) and staff were very helpful when I had questions about the data last year, but their state is rather disorganised and badly or wrongly labelled. I really hope they take a leaf out of the North Americans’ book and make available their E-ELT site test results to the community, both with detailed peer-reviewed publications and by making the data publicly accessible.
As Schöck and colleagues rightly point out in their paper, there are many ways to analyse and interpret a given dataset, and perhaps the data can be useful to scientists in ways that go beyond what the initial site testing survey had envisaged. Furthermore, perhaps data from sites that were not selected can be useful for smaller countries or institutes looking for an astronomical base but lacking the resources to fund an expensive test campaign.
The bottom line to the story is that the data from the TMT test campaign show Armazones to be a fine observing site, on first glance rather comparable to nearby Paranal – and from a purely scientific view considerably better than La Palma. I look forward to hearing about a final decision for the home of the E-ELT.
Image: ESO/M. Tarenghi
References
M. Schoeck, S. Els, R. Riddle, W. Skidmore, T. Travouillon, R. Blum, E. Bustos, G. Chanan, S. G. Djorgovski, P. Gillett, B. Gregory, J. Nelson, A. Otarola, J. Seguel, J. Vasquez, A. Walker, D. Walker, & L. Wang (2009). Thirty Meter Telescope Site Testing I: Overview arXiv: 0904.1183v1
Els, S., Travouillon, T., Schöck, M., Riddle, R., Skidmore, W., Seguel, J., Bustos, E., & Walker, D. (2009). Thirty Meter Telescope Site Testing VI: Turbulence Profiles Publications of the Astronomical Society of the Pacific, 121 (879), 527-543 DOI: 10.1086/599384
Skidmore, Warren, Els, Sebastian, Travouillon, Tony, Riddle, Reed, Schöck, Matthias, Bustos, Edison, Seguel, Juan, & Walker, David (2009). Thirty Meter Telescope Site Testing V: Seeing and Isoplanatic Angle PASP, 121 (884), 1151-1166 : 10.1086/644758
Travouillon, T., Els, S., Riddle, R., Schöck, M., & Skidmore, W. (2009). Thirty Meter Telescope Site Testing VII: Turbulence Coherence Time Publications of the Astronomical Society of the Pacific, 121 (881), 787-796 DOI: 10.1086/605295
Comments»
Hi sarah,
when searching about tolonchar site altitude, I found your blog by accident.
Nice and informative.
Cheers
Eric
[...] Jordskorpans största teleskop för synligt ljus ska bli E-ELT, European Extremely Large Telescope, med sin planerade spegel på 42 meter. Så är tanken i alla fall och 2010 är avgörandets år för projektet. Planerna är långt framskridna men ännu upp till diskussion är var teleskopet ska byggas, och hur det ska finansieras. När det gäller stålarna så ser det ut som om medlemsländernas avgifter till Europeiska sydobservatoriet ESO kommer att behöva höjas. Snart kommer Vetenskapsrådet att besluta om Sverige ska vara med i projektet. I maj ordnas en hearing i Stockholm i frågan, enligt mina källor på VR. Den roligare frågan om E-ELT:s läge kom idag närmare ett svar. En ESO-utredning har kommit fram till vilken som är den bästa av de platserna på kortlistan – fem i Chile och en på Kanarieön La Palma. Vinnaren såhär långt är berget Cerro Armazones, som ligger i norra Chile, nära Paranalobservatoriet och jätteteleskopkvartetten VLT (och helt i linje med tidigare skvaller). Se pressmeddelandet hos ESO. Därmed får det anses vara kört för platserna i Argentina och Marocko som tidigare föreslagits. Spanien däremot är inte uträknat. Enligt utredningen har alla platserna på kortlistan, inklusive La Palma, sina förtjänster. Cerro Armazones vinner på en jämn hög standard på sina natthimlar, samt just närheten till VLT. I Spanien är kampen om E-ELT en het fråga och den spanska regeringen har satsat mycket för att få bygga teleskopet på La Palma. Några som inte brydde sig lika mycket var fotbollslaget Real Madrid. Laget fick enligt nyhetsrapporter en förfrågan om att ta på sig specialgjorda tröjor till stöd för ett E-ELT på La Palma, men man vägrade klä om sig för teleskopets skull. Mer om E-ELT hos ESO Astronomen Sarah Kendrew tycker att ESO borde vara öppnare med man gjort valet [...]
[...] expected, ESO Council have accepted the recommendation to build the European Extremely Large Telescope at Cerro Armazones in the Chilean Andes. The [...]