ESO/Cou-1296 conf. Date: 19.03.2010
EUROPEAN ORGANISATION FOR ASTRONOMICAL RESEARCH IN THE SOUTHERN HEMISPHERE ______
VOTING PROCEDURE: FOR Two-thirds Majority APPROVAL of all Member States
Council (Extraordinary Meeting) 116th Council (Extraordinary) Meeting Garching, 26 April 2010
THE SITE FOR THE EUROPEAN EXTREMELY LARGE TELESCOPE
Council is invited to select Cerro Armazones in Chile’s Region II as the baseline site for the construction of the E-ELT.
European Organisation for Astronomical Research in the Southern Hemisphere ESO/ Cou-1296 conf. Page 1
Contents
1. Introduction ...... 2 2. Site characterization ...... 2 3. Relative costs of construction and operations ...... 4 3.1 Construction ...... 4 3.2 Operations ...... 4 4. Conclusions of the Site Selection Advisory Committee ...... 5 5. Chile ...... 6 5.1 Offer ...... 6 5.2 Comments ...... 7 6. Spain ...... 9 6.1 Offer ...... 9 6.2 Comments ...... 10 7. Development of the Organisation ...... 11 8. Global Perspective ...... 12 8.1 Today ...... 12 8.2 Two competing projects ...... 12 8.3 North or South? ...... 12 9. Funding ...... 13 10. Conclusions ...... 14 11. Council Action ...... 14 Annex 1 Status Report by the SSAC Annex 2 Offer by the Chilean government Annex 3 Offer by the Spanish government
European Organisation for Astronomical Research in the Southern Hemisphere ESO/ Cou-1296 conf. Page 2
1. Introduction
In 2004 Council adopted as its highest priority strategic goal for ESO the retention of leadership in the era of extremely large telescopes (Cou-991rev). The precursor studies on the 100m OWL telescope and other concepts were followed by a full Phase B design study for the E-ELT, with as baseline an adaptive telescope with a 42m segmented primary mirror, equipped with a powerful suite of instruments built in collaboration with institutes in the Member States. The Phase B study started in 2007, and will be completed in the course of 2010.
It was understood from the start that the E-ELT will be the world’s largest, most advanced and most powerful optical/infrared telescope, and that it should therefore be constructed on the best site possible, as an integral part of ESO’s overall long- term program. An extensive site characterization effort was carried out with the support of a Site Selection Advisory Committee (SSAC), consisting of independent experts who agreed to treat all data and deliberations in confidence. The SSAC assisted ESO in assessing the atmospheric quality of the potential sites as well as the logistical requirements and relative costs of E-ELT construction and operations.
2. Site characterization
The E-ELT site-testing campaign evolved from the FP6-supported collaborative program that was initiated in 2004 in the context of the OWL study, following earlier ESO efforts to find promising sites for astronomy. Four identical instruments for measuring the atmospheric turbulence profile were constructed and subsequently deployed on Aklim (Morocco), El Roque de los Muchachos on La Palma1 (Spain), Sierra de Macón (Argentina) and Cerro Ventarrones (Chile Region II). The instruments started taking data in late 2007.
After the first year of measurements it became clear that the quality of the atmosphere above Aklim and Sierra de Macón is inferior to that above the other sites. Upon recommendation by the SSAC these two sites were therefore dropped from further consideration, although data-taking continued until the end of the FP6 activities in June 2009. An agreement between ESO and the Thirty Meter Telescope project (TMT) allowed inclusion of TMT’s measurements for Cerro Armazones and Cerro Tolonchar in Chile’s Region II. Data taken on Cerro Vizcachas on ESO’s La Silla property in Chile’s Region IV were also included. These data sets were carefully correlated with the FP6 measurements. The extensive historical records for Cerro Paranal and for several telescopes on La Palma were also used, as was data taken over a long period by weather satellites and atmospheric models that allow prediction of conditions until 2050. In the course of 2009 the SSAC asked for one more site in Chile to be studied, Cerro Vicuña MacKenna, also in Region II.
The final site characterization effort therefore focused on four sites in Region II of Chile (Armazones, Ventarrones and Vicuña MacKenna near Paranal and Tolonchar south of Peine near the Salar de Atacama, see Figure 1), Vizcachas and La Palma.
1 Following the wording used in the SSAC Status Report, the phrase ‘El Roque de los Muchachos on La Palma’ is in nearly all occurrences abbreviated to ‘La Palma’ in this document. European Organisation for Astronomical Research in the Southern Hemisphere ESO/ Cou-1296 conf. Page 3
Figure 1. Location of Armazones, Tolonchar, Ventarrones and Vicuña MacKenna in Chile’s Region II. Paranal and the ALMA site are also indicated.
A full analysis of the measurements of atmospheric turbulence, weather statistics, temperature variations, humidity, and the presence of strong winds and/or dust was carried out by the E-ELT project and the SSAC. The main results, taken from the SSAC Status Report reproduced in Annex 1, are as follows:
The three sites near Paranal all have clear skies usable for science with the E-ELT for about 90% of the time. For Vizcachas and Tolonchar this fraction drops to 84% and 80% respectively, while for La Palma it is 72%. These fractions take into account high humidity and strong winds, but not the presence of dust. The latter is of particular concern for the E-ELT with its ~1000 mirror segments which are not easily cleaned in a short time. Dust is not a factor for the sites near Paranal or for Vizcachas. It has a minor impact on Tolonchar, but is significant for La Palma (notably in the summer), lowering the fraction of usable time to well below 70%.
Armazones and Tolonchar have the best seeing (median value ~0.″65), followed by La Palma and Vizcachas (~0.″8). The coherence time of atmospheric turbulence is longest on La Palma (during some months of the year), with Armazones coming in second. The sky background above La Palma is brighter than it is for the sites in Chile. The fraction of time usable for mid-infrared observations is correlated closely with the altitude of the site, and is highest on Tolonchar (62%) and Armazones (49%), and lowest on Vizcachas (24%) and La Palma (21%).
Taking into account the planned instrumental capabilities of the E-ELT and the extensive design reference mission developed by the Science Working Group in 2008-2009, the E-ELT will produce ~60 nights more science time per year on the sites near Paranal than on La Palma, in better overall conditions. For Vizcachas and Tolonchar this difference reduces to ~45 and ~30 nights extra, respectively. European Organisation for Astronomical Research in the Southern Hemisphere ESO/ Cou-1296 conf. Page 4
3. Relative costs of construction and operations
The E-ELT project carefully analyzed the differences in cost of constructing and operating the E-ELT on the various sites, and the SSAC reviewed the results independently. Detailed estimates were done for all aspects, including the cost of electrical power, fuel, water, fire fighting (including relative risk), earthquake impact, snow and ice build-up on the dome, insurance, handling of materials, accessibility, needs during construction for accommodation and transport, accommodation for staff during operations, the number of staff, the optimal shift-work system, and various other local and off-site support needs.
The cost differences between Armazones, Ventarrones and Vicuña MacKenna are fairly insignificant. As it was already becoming clear that Vizcachas would not be amongst the top sites, the detailed comparison was therefore done between Armazones, Tolonchar and La Palma, with Armazones taken as reference.
3.1 Construction
Armazones benefits from the proximity to Paranal, and the cost assessment assumes that various technical support facilities including the control room will be on Paranal. Being an isolated, bare mountain there are few if any constraints on the area and schedule of construction activities, minimizing risks and construction time.
Tolonchar is an unoccupied and isolated 4480m high mountain located in a remote area in Chile. This leads to additional construction costs of ~53 M€ (compared to Armazones) caused by longer supply lines, and the required extra staff and mountain allowances needed for working at high altitude.
For La Palma the additional cost of construction is about 25 M€. The bulk of the difference with Armazones comes from the increased cost of manpower and of construction materials. The quoted amount does not include the significant cost of upgrading the existing infrastructure on La Palma (which would be borne by Spain, Section 6), nor the costs associated with the schedule constraints resulting from undertaking a giant construction project in the middle of an operating observatory.
The extra cost required to protect the E-ELT from the seismic risk in Chile (not needed on La Palma), just as was done for the VLT, is very similar to the extra cost required to protect the E-ELT from ice and dust on La Palma (not needed in Chile).
3.2 Operations
Ignoring the cost of power supply, operating the E-ELT on Tolonchar would be ~5.5 M€/yr more expensive than on Armazones, mainly caused by the increased staff complement and associated costs resulting from the need to work at high altitude. Operating the E-ELT on La Palma would cost ~8.5 M€/yr more than on Armazones. The main reasons for this difference are the higher staff salaries on La Palma, the need for extra staff in Administration, Human Resources and Logistics to deal with rules, regulations and procedures in an additional Host State, and higher costs for procurement of goods and services. Both cost comparisons include a European Organisation for Astronomical Research in the Southern Hemisphere ESO/ Cou-1296 conf. Page 5 conservative estimate of ~1 M€/yr in annual savings, mostly in staff costs, provided by direct operational synergy of Armazones with Paranal.
The E-ELT will consume 36 GWh of power per year (10 MW peak). If Armazones is connected to the Chilean electrical grid (Section 5), and if the existing power line on La Palma would likewise be upgraded to the requirements of the E-ELT (Section 6) then the total operational costs on La Palma would be ~9 M€/yr more than on Armazones, based on the cost per kWh on La Palma and in Chile (in 2010 prices).
If both Armazones and La Palma ran on island-mode power as Paranal does today, then the operations costs on Armazones would increase by ~5.5 M€/yr and on La Palma the increase would be ~5 M€/yr. Island-mode power on Tolonchar would be more expensive than on Armazones, but connection to the Chilean electrical grid would keep the total operational costs below those for La Palma.
4. Conclusions of the Site Selection Advisory Committee
Based on the results of the site-characterization campaign and of the comparison of costs for construction and operations of the E-ELT, the SSAC concludes the following (see Annex 1 for the Status Report and the full Executive Summary):
1. Armazones is the best site for construction of the E-ELT. Its generally outstanding atmospheric conditions combined with the excellent opportunities for operational and scientific synergy with the telescopes on Paranal and its overall cost effectiveness make it the clearly preferred location.
2. Tolonchar is a similarly excellent site for its very good atmospheric conditions and is the best site for mid-infrared observations. However, the additional costs associated with the construction and operation of a new observatory on a very remote and high-altitude site reduce Tolonchar’s overall attractiveness compared to Armazones.
3. Ventarrones offers very good observing conditions but is less attractive than Armazones because the atmospheric turbulence has a prominent surface layer. Vicuña MacKenna is very likely to be a similarly good back-up to the two top sites. Both sites offer the advantage of good synergy with Paranal.
4. La Palma and Vizcachas are both good astronomical sites but do not match the excellent conditions of the top sites nor the high standards required for the E-ELT. La Palma benefits from low turbulence and long coherence times at high altitude, but has a relatively modest fraction of clear weather, poorer properties for mid-infrared observations and a much reduced scientific and programmatic synergy with other ESO facilities. Like the other Chilean sites, Vizcachas benefits from overall good sky quality, a high fraction of clear weather, and strong scientific synergy with the ESO telescopes, ALMA, and the future Large Synoptic Survey Telescope (LSST) and the Square Kilometer Array (SKA), but with average seeing and poorer mid-infrared properties. Neither Vizcachas nor La Palma is recommended for construction of the E-ELT. European Organisation for Astronomical Research in the Southern Hemisphere ESO/ Cou-1296 conf. Page 6
5. Chile
5.1 Offer
The Chilean government has repeatedly expressed its strong desire for the E-ELT to be located in Chile. ESO’s formal point of contact is the Ministry of Foreign Affairs, and over the past year a number of discussions took place with the Foreign Minister, with the Secretary General of the President’s Office, and with the President herself. Chile’s offer is summarized in a letter dated 12 February 2010, attached as Annex 2. The main elements of the offer are outlined below.
1. Donation of 189 km2 of land contiguous to ESO’s Paranal property containing Armazones, and an additional free concession of 362 km2 surrounding this in order to further limit the possibilities for outside interference. The total area of 551 km2 (Figure 2) would be added to ESO’s 700 km2 Paranal territory in April 2011 when the current concession of much of this area to Universidad Católica del Norte (UCN) in Antofagasta expires. ESO is asked to find a satisfactory arrangement for the future of the Bochum University telescopes located on Cerro Murphy 1 km south-west of Armazones which are being used partially in collaboration with UCN. The whole area may become part of a larger scientifically protected area (which extends the similar area already so designated by the Chilean government in 1991 at ESO’s request).
Figure 2. Proposed extension of the territory of the Paranal Observatory.
European Organisation for Astronomical Research in the Southern Hemisphere ESO/ Cou-1296 conf. Page 7
2. Application of the same rules for observing time for Chilean astronomers that apply to the VLT and the VLTI, namely that up to 10% of the time is reserved for meritorious Chilean proposals (as judged by the ESO Observing Programmes Committee), of which at least half are for collaborative projects with astronomers in the Member States. The government has moreover expressed a willingness to discuss this further in the Joint Committee ESO- Chile in order to strengthen the Chilean collaboration with the ESO Member States, and possibly introduce changes for the Chilean observing time on the Paranal telescopes before the E-ELT is constructed.
3. In-kind contributions to construction and operations, including maintenance and upgrade of the newly paved road to Paranal, improving (fiber) connectivity for data transfer, and an intent to enable the connection of the Paranal Observatory to the Chilean electrical grid in the near future, with the various options to be clarified before E-ELT construction starts.
4. Cooperation in science and technology, through the establishment of a Chilean innovation fund for the development of astronomy and related technologies. The fund is to be used, with an ESO financial contribution, for the training of scientists, engineers and technicians, the development of instrumentation and for improving efficiency of the construction and operations of the E-ELT. In addition, access of Chilean industry to Calls for Tenders for the E-ELT is requested, either on their own or in partnership with industry in the Member States.
5.2 Comments
The operations of the VLT on Paranal and the role of Chile are governed by the Interpretative, Supplementary and Amending Agreement to the Convention between the Government of Chile and ESO of 1963, concluded in 1995, and ratified by the Chilean Parliament. It allows the addition of new telescopes, which should normally reserve 10% of the available observing time for Chile. Modification of the fraction of observing time for Chile is possible under this Agreement, provided it is agreed in the Joint Committee ESO-Chile. This has bearing on the first two components of the Chilean offer, all four of which are commented on below:
1. Extension of ESO’s Paranal territory, and location of the E-ELT on it, is in line with the 1995 Agreement. ESO would need to formally notify the Chilean government that it will build a new telescope in the (extended) Paranal Observatory, but no new Agreement would need to be concluded, avoiding a lengthy process of parliamentary approval before construction could start.
The commercial value of the 189 km2 to be donated is ~24 M€, according to an estimate by the Chilean government. The surrounding concession of 362 km2 would normally require an annual fee of ~3% of the commercial value (~46 M€). As such, the free concession represents ~1.4 M€/yr in value.
Constructive discussions with Bochum University and UCN have been initiated, with as common goal to agree on a good solution before E-ELT construction starts. European Organisation for Astronomical Research in the Southern Hemisphere ESO/ Cou-1296 conf. Page 8
2. The proposed application of the VLT rule for Host State time on the E-ELT is a concession by Chile, by not demanding 10% of the available time without conditions, but allowing at least half of this in collaboration with the Member States. Discussions with the Chilean astronomical community indicate a willingness to consider this matter further for the VLT, VLTI, VISTA, VST and E-ELT, and the Joint Committee ESO-Chile will take this up shortly.
3. The proposed facilitation by the Chilean government of the energy supply to Paranal is a delicate issue as the production and provision of energy in Chile is privatized. The Chilean government is actively investigating technical possibilities for the power distribution, and has received four written expressions of interest from the energy sector to connect Paranal and Armazones to an existing power production substation. One option would be to connect Paranal to the central Chilean grid via a 42 km line coming up the coast from Paposo north of Taltal, and extending it by another 21 km from Paranal to Armazones. The commercial cost of installing such a line is estimated at ~15 M€. It is possible that this will be subsidized by Chile but this needs further clarification.
This connection would lower the operational costs on Paranal today by about 1 M€/yr (based on the price per kWh provided by the multi-fuel turbine and the price to be offered via the central Chilean electrical grid as communicated by the Chilean government). It would lower the operational costs of the E- ELT by ~5.5 M€/yr (in 2010 prices, see Section 3). Over the nominal thirty year lifetime of the E-ELT, this represents a significant financial contribution.
Fiber connectivity to Paranal and Armazones is already being provided through the EVALSO project, in which Bochum University is a partner. Maintenance by Chile of the part outside the Paranal territory is welcome.
4. Chilean involvement in instrumentation development has traditionally been limited but recent activities for ALMA (Band 1) and for the E-ELT instrument studies (SIMPLE) are a positive step in this direction.
ESO currently contributes annual funds to strengthen Chilean astronomy. Strategic application in the direction outlined in the Chilean offer is possible without increasing the total.
Chile already participates in Calls for Tenders for goods and services and for construction projects such as the Santiago Central Office building for ALMA on the Vitacura premises. This is in line with ESO’s Financial Rules and Regulations. The wish to participate in E-ELT contracts is aimed at strengthening the technological base in Chile, by competing and collaborating with industry in the Member States. The likelihood that this will have a significant impact on the industrial return to the Member States is modest. It is noted that if Brazil were to join ESO as Member State (see Section 9 and Cou-1287 conf.), it would no doubt obtain a significant part of the industrial return currently going to Chile.
European Organisation for Astronomical Research in the Southern Hemisphere ESO/ Cou-1296 conf. Page 9
The SSAC concluded that Tolonchar is also an excellent site for the E-ELT, with more mid-infrared time than on Armazones at the expense of a somewhat reduced fraction of clear nights. Gaining access to Tolonchar has not been discussed in detail with the Chilean government, as it became clear early on that the costs for construction and operations are substantially higher due to longer supply lines and the added cost of working at high altitude (Section 3). Building the E-ELT on Tolonchar would clearly constitute the development of a separate observatory, which would require a new agreement with the Chilean government and subsequent parliamentary approval. Measures would also have to be taken to retain good relations with the local community. All of this would take time and add further cost.
The two back-up sites Ventarrones and Vicuña MacKenna are both near Paranal, and could in principle be included in an extension of the Paranal territory as proposed here for Armazones, and hence also in line with the 1995 Agreement. Operational synergy with Paranal would be possible, but would be less than for Armazones because of the larger distance.
Finally, it is instructive to compare the Chilean offer to host the E-ELT with the Chilean position during the negotiations in 2009 to bring the TMT to Armazones. It is ESO’s understanding that Chile offered a ~5.5km2 area surrounding Armazones in concession for an annual fee, requested 10% of the observing time for Chilean astronomers to be allocated by the Comisiόn Nacional de Investigaciόn Científica y Technolόgica (CONICYT), and asked for significant annual cash contributions to CONICYT and UCN to benefit astronomy in Chile, for an estimated total cost to TMT of ~0.5 M€/yr and up-front costs of ~4M€. The project’s decision to decline this offer and locate the TMT on Mauna Kea instead has certainly influenced the Chilean government’s offer to ESO regarding the E-ELT in a positive way.
6. Spain
6.1 Offer
The Spanish Council delegation indicated during the December 2008 Council meeting that Spain would welcome the construction of the E-ELT on La Palma, provided it is amongst the best sites identified by the SSAC, and would be willing to provide significant additional funding if the E-ELT were placed on La Palma.
In the course of 2009, a Spain-ESO working group analyzed physical requirements (footprint, geology, infrastructure required), logistics (access requirements, construction conditions) and legal requirements (privileges and immunities). A draft offer (dated 30 November 2009) was sent to the Executive in early December 2009, together with a statement that clarification on the amount of potential additional funding would follow in due course. The Executive visited the State Secretary for Research twice to discuss the Spanish offer. The Minister of Science and Innovation formalized the offer by letter on 25 February 2010. This letter and the supporting document of 30 November 2009 are attached as Annex 3. European Organisation for Astronomical Research in the Southern Hemisphere ESO/ Cou-1296 conf. Page 10
The main elements of the Spanish offer can be summarized as follows: Spain will provide free access to ~0.1 km2 land for the construction of the E-ELT and for support facilities in other locations, will grant ESO autonomy and the required immunities and privileges, and will encourage the local authorities to speed up various administrative approval procedures. For the E-ELT it will waive the traditional 20% of observing time on La Palma telescopes reserved for the Host State. It will guarantee access to the site by maintaining and upgrading, when necessary, the existing access roads. Spain will also build or upgrade, free of charge to ESO, a number of basic and advanced infrastructures, including a permanent power line capable of carrying 10 MW, water provision and drainage structure and a fast data link to mainland Europe under the IRIS NOVA II project. The Spanish government values the proposed infrastructure upgrade at about 50 M€, and will offer up to 250 M€ in-kind contributions for construction of the E- ELT, with the specifics to be negotiated.
6.2 Comments
Donation of public land is not possible under Spanish law, hence the land for the construction and operations of the E-ELT is offered in concession. A suitable site for the E-ELT has not been identified because the best sites are already occupied and the area required for the E-ELT construction is substantial.
The waiving of Host State observing time for Spain would make all the observing time on the E-ELT available in open competition to the Member States (including Spain). Given the difference in clear weather fraction with Armazones, this would still be less than for the E-ELT placed on Armazones, even after taking into account the fact that some of the time would go to Chilean astronomers and perhaps to a new Member State.
The suggested infrastructure contributions would provide savings of 10-15 M€ in the construction budget of the E-ELT. This amount was already taken into account in the computation of the total additional construction cost of 25 M€ as compared with construction on Armazones (Section 3.1). The upgrade of the existing power line to 10 MW capacity would help to limit the additional cost of operations compared to Armazones to 9 M€/yr (Section 3.2).
A contribution of up to 250 M€ in-kind towards construction is generous, and could be a large step towards fully funding the construction of the E-ELT. This however would need the identification of enough in-kind contributions from Spain that would not interfere with the industrial return to other Member States in an undesirable direction. This would need careful analysis and discussion.
Finally, it is by no means evident how to construct the E-ELT in the middle of a working observatory with telescopes operated by different international consortia without causing significant and lengthy disruptions (either to the other telescopes or to the E-ELT construction schedule). The practical implementation of the suggested sharing of facilities with the Instituto Astrofísica de Canarias (as described in Annex 3) would also need clarification.
European Organisation for Astronomical Research in the Southern Hemisphere ESO/ Cou-1296 conf. Page 11
7. Development of the Organisation
ESO’s original purpose was to build, equip and operate a powerful observatory in the Southern Hemisphere. This was achieved with the creation of the La Silla Observatory, supported by the ESO Office in Vitacura. It was followed by the construction of the VLT on Paranal in the nineties. APEX was added to the ESO program in 2002, with a support base in Sequitor and the 12m sub-millimetre antenna on a small concession on Llano Chajnantor, now surrounded by the global ALMA project in which ESO represents Europe. With Headquarters in Garching, and not counting small offices in La Serena and Antofagasta, this means ESO currently operates five sites. Council has indicated on several occasions that it does not favour a further increase in the number of sites.
The decision to put the VLT, VLTI, VST and VISTA all on Paranal was the correct one, but it had as an inevitable consequence that the centre of ESO’s activities shifted from La Silla to Paranal, leading to a reduction of activities on La Silla, and a different role for the remaining medium-sized telescopes in ESO’s overall program.
Putting the E-ELT on either Tolonchar or La Palma would necessitate opening another ESO site. On La Palma this would mean developing a site in the middle of an existing observatory and in a different Host State which is also a Member State. This would complicate ESO’s internal organisation by spreading it out further, and would require substantial additional efforts in Administration, Human Resources and Logistics (included in the higher operations costs reported in Section 3.2). It would also threaten the long-term future of Paranal, as the new flagship facility would be in another Hemisphere at a significant additional cost, so that pressure on the Paranal budget would mount and operations, maintenance and upgrades would suffer.
In contrast, the addition of the E-ELT to the Paranal Observatory would not open another site, but would further strengthen Paranal with a unique additional capability which would be part of its world-leading integrated system, thus ensuring a highly- productive long-term future. The integration of the E-ELT into ESO’s end-to-end operations model is straightforward if the E-ELT is operated from Paranal where the required science operations infrastructure from control room to dataflow system already exists. It would also provide a natural way of making optimal use of the very strong operational and engineering skills available on Paranal. The engineers involved in integrating the complex second generation instruments for the VLT and the VLTI as well as PRIMA and the Adaptive Optics Facility would be well-prepared and highly-motivated to take on the challenge of integrating and operating the E-ELT and its instruments.
It is not unlikely that by the time the E-ELT is constructed, APEX will be discontinued and La Silla is no longer a factor in the ESO budget, so that ESO would run the Paranal Observatory, support its share of ALMA operations (via the Santiago Central Office in Vitacura), and could take on a new ambitious project reasonably soon after. European Organisation for Astronomical Research in the Southern Hemisphere ESO/ Cou-1296 conf. Page 12
8. Global Perspective
8.1 Today
There are currently a dozen 8-10m class telescopes in the world, with two prime centres. One is Mauna Kea with the twin 10m Keck telescopes, the 8.2m Subaru telescope and the 8.2m Gemini North telescope. The other is Paranal, built as a single integrated system of the four 8.2m telescopes comprising the VLT, together with the VLTI, VISTA and the VST. Paranal is widely acknowledged to be the world’s most advanced ground-based astronomical observatory.
Other large optical-infrared telescopes are the 10.4m GranTeCan on La Palma, the Large Binocular telescope on Mount Graham, and the 8.2m Gemini South telescope on Cerro Pachón. The Hobby-Eberly Telescope in Texas and the South African Large Telescope are in the same aperture class but are not fully steerable.
8.2 Two competing projects
The TMT project plans to put a 30m telescope on Mauna Kea. In principle this makes it possible to develop the set of large telescopes there into a strong system. This will be challenging as the 8-10m telescopes are currently operated by three different partnerships which overlap with but are not identical to the TMT partnership. If achieved, then Mauna Kea would continue to be the leading observatory in the Northern Hemisphere.
A consortium led by the Carnegie Observatories plans to put the 22m Giant Magellan Telescope (GMT) on Las Campanas near La Silla, which already hosts the twin 6.5m Magellan telescopes. Together with Gemini South and the future 8.4m LSST, also to be placed on Cerro Pachón, this would provide substantial non-ESO observing capabilities in the South, mostly complementary to the VLT.
8.3 North or South?
The VLT and ALMA are both in the South (-25o and -23o latitude, respectively), as will be the major future ground-based facilities LSST and SKA (if funded). While there is partial overlap in sky accessibility with Mauna Kea (+19o) this is more modest for La Palma (+28o).
Putting the E-ELT on El Roque de los Muchachos might ensure a long-term future for the non-ESO telescopes on La Palma. Even if these could be integrated into a system, it would be unlikely to be able to compete effectively with Mauna Kea, despite the power of the E-ELT, and would furthermore lead to the undesirable situation where the two largest optical/infrared telescopes in the world would be in the North while all the other major ground based facilities would be in the South, severely hampering scientific synergy. And Paranal would similarly have a very hard time competing with Mauna Kea with the TMT. European Organisation for Astronomical Research in the Southern Hemisphere ESO/ Cou-1296 conf. Page 13
In contrast, integrating the E-ELT into the Paranal system will guarantee the long- term undisputed world-wide scientific dominance of the Paranal Observatory, and enable ESO to continue world-leading studies of the Southern sky, fully in line with its purpose and with maximum scientific synergy with ALMA, LSST and SKA. The crucial importance of this synergy was already pointed out in the December 2008 report to Council by the E-ELT Standing Review Committee (Cou-1233).
9. Funding
The baseline funding scenario for the construction of the E-ELT was noted by Council in June 2009 (Cou-1248). It foresees a contribution of approximately 300 M€ from the projected ESO income until 2020 assuming the current 14 Member States and the normal annual correction for cost variation. Added to this is a foreseen extra contribution from the Member States, consisting of a 2% year-on- year increase (for a decade) of the regular annual contributions and a lump sum of at most 250 M€. The remaining 300 M€ can in principle be borrowed (an offer is in hand from the European Investment Bank), but the goal is to avoid (or at least minimize) this by means of contributions of new Member States and/or partners and/or the Host State. Recent progress in this direction is summarized in Cou-1287 conf., with a verbal update provided during the Committee of Council meeting on 2 March 2010. This included an expression of interest in participation in ESO’s program by the government of Brazil, provided the E-ELT is placed in Chile.
The bulk of the E-ELT construction funding will be spent on industrial contracts in the Member States. The Host State gains advantages, as part of the construction (e.g. civil works) will of necessity be carried out by local companies. Similarly, many goods and services needed for operations will be supplied locally, and the E-ELT staff will spend (part of) its salary locally. In round numbers, the E-ELT may inject 20+ M€/yr into the local economy during operations (which are expected to continue for 30 years - if not longer) and another 100+ M€ during construction.
Spain’s offered in-kind contribution might just allow construction of the E-ELT on La Palma, but this financial advantage would essentially be lost as a result of the substantially increased cost of operations over 30 years. Moreover, the same total cost of construction and operations would result in significantly fewer nights/year of observing time on the E-ELT on a site that is not nearly as good as Armazones. It would also lead to a dispersion of activities and loss of focus in the Organisation and would have a detrimental effect on the Paranal Observatory, putting at risk the world-leading integrated system that has made ESO so effective.
The Chilean contributions are very significant, but do not solve the need for additional construction funding. Putting the E-ELT on Armazones would clearly maximize the scientific return while minimizing the overall cost of the project (construction and operations).
European Organisation for Astronomical Research in the Southern Hemisphere ESO/ Cou-1296 conf. Page 14
The recent resurgence of interest in ESO from a number of potential new Member States is clearly connected with the general perception that the E-ELT project is rapidly becoming the most advanced of the large telescope projects, both technically and organisationally. Selection of Armazones as the site will demonstrate that ESO is intent on adding the best telescope in the world on the best site as part of the already world-leading Paranal Observatory. This will surely help in securing the required additional funds from the current 14 Member States, and is very likely to result in more than one application for ESO membership, which would go a long way towards avoiding borrowing altogether. It is clearly the right way forward, even in light of the Spanish in-kind contribution.
10. Conclusions
Based on the analysis of the atmospheric characteristics and of the costs of construction and operations, Armazones is the best site for the construction of the E-ELT, by a large margin. It provides unrivalled astronomical conditions and operational and scientific synergy with the VLT, VLTI, VISTA and VST. Adding the transformational scientific capabilities of the E-ELT to this already tremendously powerful integrated system guarantees the long-term future of the Paranal Observatory as the most advanced optical/infrared observatory in the world, offers scientific synergies with ALMA, LSST and SKA, and further strengthens ESO’s position as the world-leading Organisation for ground-based astronomy.
The selection of the site for the E-ELT could be done as part of the approval of the construction and operations of the E-ELT as a Supplementary Program. There are, however, a number of reasons for selecting the site now. It would facilitate the writing of the construction proposal with a formally selected baseline site, would (hopefully) reduce the intense media scrutiny and pressure, including activities in the European Parliament aimed at influencing the future of ESO, and would have the additional benefit of further increasing the likelihood of securing the required funding as outlined in Section 9.
If Council were to select Armazones as the baseline site, the Executive would negotiate further particulars with the Chilean government, including the donation and concession of the land containing Cerro Armazones (Figure 2), the connection of Paranal and Armazones to the Chilean electrical grid, the fraction of observing time reserved for Chilean astronomers on the Paranal telescopes including the E-ELT, and the implementation of the proposed technology collaboration.
As approval of a Supplementary Program requires a two-thirds majority of all Member States, the same voting majority is needed for the selection of the site.
11. Council Action
Based on the arguments above, Council is invited to select Cerro Armazones in Chile’s Region II as the baseline site for the construction of the E-ELT.
European Organisation for Astronomical Research in the Southern Hemisphere Annex 1 to ESO/ Cou-1296 conf.
Annex 1. Status Report by the SSAC
Annex 1 to Cou-1296 conf.: SSAC Status Report E-ELT Site Selection Advisory Committee – Status Report, March 2010 – CONFIDENTIAL
Status report of the Site Selection Advisory Committee for the European Extremely Large Telescope
March 2010
1. PREAMBLE 2
2. EXECUTIVE SUMMARY 3
3. INTRODUCTION 4 3.1 CHARGE 4 3.2 HISTORY 5 3.3 SOME NOTES ON SPECIFIC SITES 6 3.4 LESSONS LEARNED AT PARANAL 8
4. SCIENCE REQUIREMENTS AND SYNERGIES 8 4.1 OBSERVING MODES 8 4.2 SYNERGIES WITH EXISTING AND FUTURE FACILITIES 9
5. SITE TESTING METHODOLOGY 9 5.1 INSTRUMENTS AND PARAMETERS 10 5.2 OTHER INPUT 13
6. OTHER CONSIDERATIONS 16 6.1 LIGHT POLLUTION 16 6.2 SEISMICITY & VOLCANIC ACTIVITY 16 6.3 CONTRAILS 17 6.4 THE SODIUM LAYER 17 6.5 LONG-TERM CLIMATE CHANGE 18 6.6 OPERATIONAL SYNERGIES 21 6.7 CONSTRUCTION & OPERATIONS COSTS 22
7. RESULTS 22 7.1 SUMMARY OF KEY PARAMENTERS 22 7.2 SITE DESCRIPTION 24
8. DISCUSSION 27 8.1 COMPARISON OF MOST RELEVANT PARAMETERS 27 8.2 THE TIME DOMAIN 29 8.3 COMPARISON WITH THE TMT & GMT SITES AND PARANAL 29
9. RECOMMENDATIONS 30
10. ACKNOWLEDGEMENTS 33 REFERENCES 33
1 Annex 1 to Cou-1296 conf.: SSAC Status Report E-ELT Site Selection Advisory Committee – Status Report, March 2010 – CONFIDENTIAL
1. PREAMBLE
This confidential document, delivered to the ESO Director General, is a Status Report, dated March 2010, of the Site Selection Advisory Committee for the European Extremely Large Telescope. Completing the SSAC’s task requires a more extensive discussion and presentation of some aspects of site characterization, as well as the analysis of the last few months of site testing data. Although work is ongoing, the Committee believes that the main conclusions and recommendations are robust and are not likely to change. A public version of the report will be published once our task has been finalized.
E-ELT Site Selection Advisory Committee March 2010
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2. EXECUTIVE SUMMARY
This report presents the progress of the work and conclusions from the ESO E-ELT Site Selection Advisory Committee (SSAC), whose task it was to advise the ESO Director General on the best possible location for the future European Extremely Large Telescope. The committee’s conclusions are based on a critical and objective assessment of the extensive and intense site testing initiative led and coordinated by ESO. Our conclusions not only take into account the wide range of astronomically relevant atmospheric parameters, but also aspects related to the construction and future efficient operation of the facility.
Our key conclusions are summarized as follows:
1. Of the sites considered, Armazones and Tolonchar are found to be excellent locations for the E-ELT based on their atmospheric conditions. Of these two top locations the SSAC strongly favours Armazones as the prime site for the construction of the E-ELT. Its generally outstanding atmospheric conditions combined with the excellent opportunities for operational and scientific synergy with the Paranal Observatory and its overall cost effectiveness make Armazones the clearly preferred location.
2. Tolonchar is also characterized by very good atmospheric conditions and is the best site for mid-IR observations. However, the potential difficulties and additional costs resulting from the development and the operation of a new observatory on a remote and high site reduce its overall attractiveness compared to Armazones. Moreover, being located in a populated area, this site has significance to the local population, which would have to be carefully addressed.
3. If Armazones and Tolonchar could not be made available for constructing the E-ELT, another site in the Paranal area would be our next preference. We feel confident that a site in this area would offer observing conditions similar to those prevailing, and exceedingly well characterized, at Paranal, and would offer a strong synergy with the Paranal Observatory. More site testing would however be required, in particular for what concerns the strength of the surface layer at a given site. At this point, two potential locations could be considered: Ventarrones, which offers overall turbulence conditions less attractive than those of Armazones, and Vicuña MacKenna for which only very limited data exit.
4. The sites of La Palma and Vizcachas (or its neighbourhood) are very good astronomical sites with a long track record of development of first class facilities and of scientific discoveries. The site of La Palma benefits from low turbulence at high altitude and long coherence times, two important assets for the operation of adaptive optics systems. However, its relatively moderate fraction of clear weather and poorer properties for mid-IR observations, combined with the much reduced scientific and programmatic synergy with other ESO facilities due to its Northern and remote location, are elements irreconcilable with the very high expectations raised by the E- ELT. Vizcachas benefits from an overall good sky quality and high fraction of clear weather, and strong scientific synergy with the La Silla-Paranal telescopes, ALMA, SKA and the LSST, but with an average seeing and poorer properties for mid-IR observations. Here again, this site does not meet the high standards required by the E-ELT and would be of significantly lower scientific value than the north-Chilean sites. We therefore do not recommend building the E-ELT on either of these two sites.
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3. INTRODUCTION
3.1 CHARGE
Selecting a location for a large astronomical telescope is a complex task that involves extensive long-term monitoring of many atmospheric parameters as well as a judgement of aspects that are not so easily quantified. The final choice of site affects fundamental aspects such as the cost and efficiency of constructing and operating the facility, and, most importantly, the science that is best done with it. Site selection for the E-ELT commenced several years ago as a truly global investigation to find the best possible location. The SSAC was constituted in the spring of 2008 to assist ESO in its quest to find the optimal place for constructing and operating the E- ELT, taking into account the full range of relevant scientific and operational issues. The formal remit of the committee was as follows:
The SSAC will advise ESO on the selection of the site for the European Extremely Large Telescope. The details of the methodology to be used will be discussed during the first meeting and agreed with ESO.
ESO will support the SSAC by providing regular updates on the site characterization data collection and on the requirements of the project.
The SSAC will review the site characterization strategy and may request, through the P.I., the support of site characterization specialists to address specific issues.
The SSAC will produce a final report assessing the candidate sites according to a decision matrix. The report will include a ranking of the sites, and will be delivered to the ESO DG.
SSAC membership consisted of: Jean-Gabriel Cuby (OAMP), Roland Gredel (MPIA), Sergio Ortolani (Padova Univ.), Mark Phillips (Carnegie Observatories), René Rutten (Grantecan, chair).
The SSAC met several times face-to-face, and was in regular contact between meetings in order to assess the site testing data and their analysis, to plan and provide advise on the activities ahead, and assist the ESO-team where possible. The SSAC also visited five of the sites that were considered most important at the time.
The search for the optimal E-ELT site implied an intense effort by several people for site testing and to carry out studies on specific subjects related to the construction and operation of the future facility, including an inquiry into its future scientific scope. The SSAC received regular reports on progress of all activities, extensive bi-monthly reports on the results of the site-testing campaigns, and in-depth studies on specific aspects. In addition to data from the E-ELT campaign, advantage was taken of data such as those obtained for the TMT site testing campaigns and historic records for La Palma and Paranal.
With respect to the site testing activities, the SSAC’s aim was to have at least one full year of complete site testing data on which to base its final recommendation. Although in the course of the campaign new ideas developed and some setbacks occurred in the data collection process, the SSAC is of the opinion that our conclusions are solid.
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3.2 HISTORY
SITE PRE-SELECTION
In preparation for the search of a potential site for the ELT, ESO convened various working groups since 1995. The ESO Search for Potential Astronomical Sites (ESPAS-2000) Working Group was set up to evaluate site characterization for Extremely Large Telescopes (ELTs). The ESPAS working group report was finalised in 2000 and a library of potential sites was made available at http://www.vt-2004.org/gen-fac/pubs/astclim/espas/espas_lib.html. The ESPAS activities paved the road to the shortlist of potential sites for future giant telescopes. In the context of the study of the 100-m Overwhelmingly Large Telescope project (OWL), M. Sarazin of ESO provided a comprehensive summary of site characterisation methods in the OWL blue book, which can be accessed at http://www.eso.org/sci/facilities/eelt/owl/Phase_A_Review.html.
New sites which were being explored from the outset as potential hosts of future observatories often lack a long-term and comprehensive data basis which may be used to assess the atmospheric transparency. Even at existing astronomical sites the definition of the quality of a night in terms of ‘photometric’, ‘clear’, ‘spectroscopic’, or ‘useful’ varies to a large extent among the various observatories. This is why ESO developed, together with the University of Fribourg, the FriOWL tool in preparation of the OWL site selection (http://www.iapmw.unibe.ch/research/projects/FriOWL/). FriOWL is a composite climatologic and geomorphologic database including the ERA-40 reanalysis of climatologic data, a seismic layer at high resolution, topographical tiles at 1 km resolution, and cloud models from the Canadian Centre for Climate Modelling and Analysis. The tool allows atmospheric constraints for astronomical observations to be specified such as cloudiness, turbulence, precipitable water vapour column densities, relative humidity, low surface and jet stream wind speeds, air temperature and variability, aerosol contamination, severe weather (snowstorm, lightning) conditions, the night sky brightness, and contour maps defined by e.g. the amount of land above a certain altitude. It moreover allowed creating time series, and investigating for instance the evolution of the precipitable water vapour over a given site over the last few decades. FriOWL thus allowed identifying, on a global scale, potential sites for the next generation of large telescopes and was a useful aid for the initial search for potential sites.
THE ELT DESIGN STUDY
In the meantime, ESO successfully submitted to the 6th Framework Programme (FP6) of the European Commission a Technology Development Program towards a European Extremely Large Telescope (E-ELT): the ELT Design Study, coordinated by ESO, started in January 2005. One work package (WP12000), led by J. Vernin from the University of Nice, was tasked to design, build, and operate standard site testing equipment, most notably the DIMM and MASS instruments. Initially two sites were selected, one in each hemisphere, that would serve as reference points and were known for being good locations: Paranal-North (cerro La Chira) and La Palma, in the Canary Islands. Later the list was expanded and besides the two initial locations site testing was extended to Aklim, in the Moroccan southern Atlas mountains, Izaña, on the island of Tenerife, and Macon in the Argentina Andes, east from Paranal (Vernin et al., 2009).
THE E-ELT
After the OWL review in November 2005, ESO convened in early 2006 five working groups with the goal to develop the Basic Reference Design of a 40 to 60 m E-ELT – this marked the starting point of the E-ELT project. The five working groups were tasked to assemble a roadmap for the main components of the E-ELT: adaptive optics, instrumentation, site evaluation (WG3), telescope design, and science. The site evaluation working group considered various aspects of E-ELT site characterization and site selection, and provided in their final report:
• A compilation of 19 potential ELT sites; • The available sources of information on site parameters for these sites; • The available instrumentation and methodology to obtain these parameters;
5 Annex 1 to Cou-1296 conf.: SSAC Status Report E-ELT Site Selection Advisory Committee – Status Report, March 2010 – CONFIDENTIAL
• A discussion of all relevant site parameters; • The impact of various site parameters on the various ELT science cases.
The WG3 report complemented the large and comprehensive documentation on site characterisation for the various ELT projects that were available at that time (e.g. for the TMT project: Schöck, 2004).
The E-ELT baseline reference design was presented to the ESO community in a conference in Marseille at the end of the year 2006, and the ESO council subsequently granted approval for the project to proceed to Phase-B. In order to commence realistic engineering design studies, three reference sites were chosen whose site conditions were well established and representative of the range of conditions that are encountered in astronomical sites at low to mid latitudes. These reference sites were Paranal, Vizcachas and La Palma.
The ELT Design Study equipment became progressively available and was deployed on the various sites between the end of 2007 and mid-2008. In July 2008, the ESO Director General then convened the Site Selection Advisory Committee (SSAC) which was tasked to assist ESO in the analysis of the site testing campaigns and to recommend the best site(s) where to install the E-ELT.
With the E-ELT project then firmly in place and with the site testing campaigns just started, the shortlist of potential sites clearly had to be rapidly revisited, taking into account the on-going activities in the ELT Design Study framework and the thorough site testing campaigns that the Thirty Meter Telescope project had launched in the meantime, including at sites that were also prime candidate sites for the E-ELT.
FIRST DATA AND THE REFINEMENT OF THE SITE LIST
As part of the ELT Design Study, a number of cross-calibrated MASS-DIMM instruments were developed and deployed on Aklim, La Chira, La Palma, and Macon. Thanks to a collaborative agreement between ESO and the TMT project, the data for the sites of Armazones and Tolonchar, characterized by TMT since 2005 for Armazones and 2006 for Tolonchar eventually became available to ESO1; these two sites were then formally included by the SSAC in the list of potential sites for the E-ELT as both were very promising and Armazones was already well known from the VLT site-testing campaign. As part of this agreement, one TMT MASS-DIMM was also deployed on the Vizcachas site, on the ESO premises close to La Silla. Cross calibration campaigns between the various equipments, from the ELT Design Study, TMT and other ESO MASS-DIMMs (e.g. the Paranal one) were performed, and their performance were shown to be in good overall agreement (Sarazin et al. 2009).
3.3 SOME NOTES ON SPECIFIC SITES
LA CHIRA
During the first months of site testing on La Chira, it became obvious that this site suffered from mediocre conditions. Consequently, further site testing activities were discontinued and the equipment was re-deployed to Ventarrones in the first quarter of 2008.
AKLIM & MACON
In November 2008, the SSAC expressed concern about the appropriateness of the Aklim site. The delivery and installation of a DIMM from the FP6 ELT Design Study had been severely delayed and concerns were raised about the quality of the data. Seeing measurements taken until the end of 2008 were not promising. Considering that Aklim was also clearly the warmest site of all, this site was discarded and not evaluated further by the SSAC.
1 All TMT site testing data became public in January 2010. See http://sitedata.tmt.org/
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The only high-altitude site originally tested by ESO was Macon, at 4634 m. The extremely strong winds prevailing on this site (in excess of 12 m s-1, twice as much as typically encountered on the other sites) had been a serious concern to the SSAC from the beginning. After a few months of data analysis, it also became clear that the seeing conditions, in particular the free atmosphere seeing, were not at the level of quality required for the E-ELT. In the summer of 2009, the SSAC recommended to discontinue further site testing activities on Macon.
After the formal decision to withdraw the site equipment from Macon, the SSAC received a detailed summary of the studies (Garcia Lambas & Recabarren, 2009) and the results of a numerical study of the wind patterns across the Macon Ridge (Gonzalez, 2009). The numerical study confirmed the very high wind speeds that prevail near the location initially selected for site characterization, but suggested that the very high wind at the tested location results from topography alone, and that significantly lower wind speeds are to be expected at alternative sites located just a few hundred meters away. Measurements with a weather station installed at an alternative site were obtained in May 2009, and they showed that the wind speed ranged between 62–75% of its value at the site tested in the first place, in agreement with the expectations from the simulations. Finally, although Macon may be a very good site for other future telescope projects, the relatively poor free atmosphere seeing which is independent of the surface wind speed precludes it as a viable site for the E-ELT.
VICUÑA MACKENNA
Cerro Vicuña MacKenna (3100 m) is located in the vicinity of Paranal. It was considered as an option by ESO, after La Chira and Ventarrones. At that time (2008-2009), access to Armazones and Tolonchar data was not at all clear. Of the four sites (Armazones, La Chira, Ventarrones, and Vicuña MacKenna) in this same general area, Vicuña MacKenna is the most distant from Paranal and is currently the most difficult to access. The meteorological situation is expected to be very similar to Paranal, but there are no archival records on the optical turbulence.
ESO carried out two brief site testing campaigns of a few nights in May 2009 under difficult logistical conditions. The equipment included a portable DIMM with a MASS-DIMM device mounted on a 6 m tower, and a LuSci device. Simultaneous measurements were taken at Paranal and Ventarrones. The results showed marginally better seeing and coherence time at Vicuña MacKenna compared to the other two sites.
The SSAC recognized this site as a valid intermediate altitude alternative and encouraged ESO to proceed with a 6-month site testing campaign to mitigate the risk in case of problems with the other sites. However, logistics and difficulties with instrumentation availability hampered continuation of the measurements.
LA PALMA
Roque de los Muchachos Observatory on the island of La Palma remained the only potential location in the northern hemisphere on the shortlist, but there are some complications with respect to the data from this site. The dataset from La Palma lacks uniformity in particular for the characterization of optical turbulence. Systematic seeing measurements for the ELT-DS were carried out under the EU-FP6 contract. Site testing equipment was installed at a location called Degollada del Hoyo Verde (DHV), although this site was not a realistic place for the E- ELT. Measurements did not start in earnest until May 2008. In November of 2009 the equipment was moved to a new location, close to the Magic Telescopes, although it remained unclear whether this would be the final E-ELT location. This change interrupted the continuity of the already collected data. In addition, the seeing data from La Palma over the whole period of the E-ELT site testing campaign suffers from a significant paucity in the winter months causing a bias towards the summer months. We will come back to this issue in Section 7.1.
The La Palma site is also unique on the shortlist in the sense that it is the only location inside a major operational observatory. A concern is the impact the E-ELT may have on the other telescopes present at the observatory, during construction, but also during future operation.
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Airflow models that take into account the local orography and actual location of existing telescopes show a significant risk that the E-ELT dome will affect the airflow at other telescopes down wind (Tamai, private communication). In itself this is maybe not of direct concern to the E- ELT project, but is not something that can be ignored either.
3.4 LESSONS LEARNED AT PARANAL
Cerro Paranal was selected by ESO in the early 1990s as the site for the VLT after an extensive site testing campaign (Sarazin, 1990). The main criteria for the selection of Paranal over Cerro Vizcachas were photometric nights (81% vs 58%), seeing (median of 0.66″ vs. 0.76″), and precipitable water vapour (median of 2.3 mm vs. 3.9 mm). Twenty years later, it is instructive to compare these results with the data obtained in 2008-2009 as part of the E-ELT site testing campaign. The difference in precipitable water vapour remains exactly the same, but the statistics on photometric nights (77% for Paranal vs 66% for Vizcachas) and DIMM seeing (median of 0.93″ vs. 0.81″) indicate that real changes have occurred at both sites which appear to have diminished the overall difference in quality of the two sites. Indeed, if the selection for the VLT site had been based on the 2008-2009 data, it is not so clear that Paranal would have been selected.
There are two important lessons to learn from this comparison. First of all, even the best of sites can show variations in their properties with time. The significant degradation in the quality of the seeing at Paranal as measured by the facility DIMM has been shown to be associated with a secular change in the wind rose. In particular, bad seeing conditions are now known to occur preferentially when the winds are from the NNE and SSE, and such winds have become increasingly more common at Paranal during the last 15 years. Hence, no matter how carefully a site testing campaign is carried out, it is impossible to fully characterize a site based on only a few years of data. Nevertheless, we know from more than six years of observations with FORS2 on UT2 that the actual science data image quality in the R band delivered by the VLT telescopes has been excellent (median 0.65″) while the median seeing as indicated by the facility DIMM was much poorer (0.81″). As reported by Sarazin et al. (2008) this discrepancy is due to the presence of a surface layer of turbulence that is strongest when the wind blows from the NNE and SSE. Fortunately, most of the time this surface layer does not extend above the first 20 m, affecting the DIMM measurements but not the VLT telescopes. Thus, the second lesson to be learned from Paranal is the necessity of characterizing the surface layer in order to properly interpret the seeing results from a site testing campaign.
4. SCIENCE REQUIREMENTS AND SYNERGIES
4.1 OBSERVING MODES
Extensive efforts have been devoted to define the scientific and instrumentation plan for the E- ELT, with a strong involvement of the user community. Elaborating detailed ELT science cases has been a long standing endeavour of the three main ELT projects since 2000 or earlier. In Europe, a dedicated Working Group, under the auspices of the Opticon programme, was explicitly tasked to elaborate the European ELT science case. This activity culminated with the release of the first book on the science case for the European ELT in 2005 (Hook, 2005). In 2006, the Opticon WG was merged with the ESO E-ELT Science Working Group to further elaborate the E-ELT science case and to develop a Design Reference Mission (DRM). In the meantime, instrument studies were also carried out, initially as part of the ELT Design Study and later as part of the E-ELT project, leading to further insights into the E-ELT Science Case and scientific requirements.
All ELT science cases are remarkably similar, and all express a high synergy with JWST and a strong scientific interest for adaptive optics (AO) assisted observations into the near IR domain – the realm of ELTs (see e.g. Kissler-Patig et al., 2009). The main observing modes that have been identified in the E-ELT Science Case to enable the highest scientific return over its first few years of operations are:
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• Seeing limited spectroscopy at visible wavelengths; • Imaging and spectroscopy with adaptive optics in the near-IR; • Diffraction limited near-IR imaging and spectroscopy; • High-contrast near-IR adaptive optics (also known as Extreme AO or XAO); • Diffraction limited imaging and spectroscopy in the thermal-IR (mid-IR).
Defining the science that will be contemporary in ten years from now is hard enough, but is a necessary endeavour considering the long development timescales of telescopes and instruments; defining the science that will be contemporary over the whole lifetime of a facility like the E-ELT is much harder still. One should make sure that the facility will provide a large range of capabilities, beyond those initially offered. As far as sites are concerned, good weather conditions enable more science; good seeing conditions, in particular at high altitudes, enable higher contrast images or corrections over wider fields; dry, dust-free and high altitude sites enable good transparency over large spectral ranges. These certainly are high-level key scientific requirements for an ELT site, to which obvious operational requirements shall be added, such as moderate winds, air temperatures well above the dew point, stability of the observing conditions, etc.
4.2 SYNERGIES WITH EXISTING AND FUTURE FACILITIES
Astronomy has become more and more pluri-disciplinary and multi-wavelength. Synergy with other facilities is a key requirement for a general-purpose facility such as the E-ELT. For obvious reasons, the synergy with existing ESO facilities, VLT/VLTI, VISTA, and soon ALMA, but also the LSST, if built, points toward a preference for the Southern hemisphere. In the longer term, the development of SKA in the Southern hemisphere is another attractive factor favouring the South. However, some ESO member states have access to telescopes on northern sites (e.g. GTC, LBT, LOFAR, Gemini-N), and a northern site would provide better synergy with these. We note an initiative from the Spanish community in 2009 that specifically contrasted science programmes for both hemispheres, the outcome of which is reported by Herrero et al. (2009). Clearly excellent science can be done from both hemispheres, both hemispheres possess unique sources that are of interest to the E-ELT, and any telescope located at intermediate latitudes can see large parts of the sky in the opposite hemisphere.
More important, perhaps, is the fact that TMT has chosen a Northern hemisphere site, and developing both TMT and the E-ELT on the same hemisphere would clearly be counter- productive from the global astronomy perspective.
The synergy with space missions will also be extremely strong, in particular, as already mentioned, with JWST. Space missions usually do not favour one hemisphere in particular, but there are clear exceptions such as the Kepler mission that only observes objects in a small patch of the Northern sky.
Apart from the scientific synergies, we stress the potential importance of running the E-ELT and the VLT as a future coordinated operation. Sharing of infrastructure resources, accommodation, engineering staff, astronomy staff and administrative staff appears feasible and attractive if the E-ELT were to be located close to Paranal.
5. SITE TESTING METHODOLOGY
Searching for the best possible E-ELT site is primarily driven by the future operational scientific goals. Therefore an objective assessment of the site quality for astronomical observations has taken a prominent role, bearing in mind the instrumentation and observing modes that are expected to be important (see Section 4.1). But also consideration has to be given to the local conditions and circumstances that will have an impact on the optimal and efficient construction and operation of the facility. The process thus involves a large number of parameters that need
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to be considered, and involves judging and balancing sometimes conflictive aspects in the most objective way. Aspects to be considered are:
Atmospheric conditions: Cloud cover statistics, seeing, isoplanatic angle and coherence time, vertical turbulence profile, local air temperature, local wind speed, precipitable water vapour levels, humidity statistics, dark sky brightness and its future development, extinction statistics, sodium layer strength, snowfall, and local dust conditions.
Geology and geography: Available space, bedrock and soil conditions, seismic and volcanic activity, general orography.
Location: Latitude and accessibility of declination range, synergy with other key astronomical facilities, air traffic, potential local restrictions or complications for constructing or operating the facility, space availability for future extension of the site and potential development of accompanying facilities.
Infrastructure: Roads, airport, seaport, electricity, water, data transmission, medical facilities.
Developments: Population, light pollution, tourism, infrastructure, mining or industrial activities, cultural or archaeological significance to the local population.
The various parameters are not equally important for the different science cases that are pursued with the E-ELT. While it is clear that a high, cold and dry site with little atmospheric turbulence will serve all needs, operational aspects and cost will establish the need to evaluate lower, warmer sites. In the latter case, a compromise must be found for the needs of the various science cases. A first effort to find a site that provides such a compromise was undertaken by the E-ELT – WG3 that evaluated the impact of the various site parameters on the different science cases that were proposed for the OWL project. The task of weighting some of the key astronomical site parameters has been brought to maturity by Melnick & Monnet (2010) in their formalism of the ELT Merit Function and is described in more detail in Section 8.1.
5.1 INSTRUMENTS AND PARAMETERS
The objective of the site testing initiatives was to deploy (near) identical instruments on each site and where necessary and feasible, to cross calibrate these. Basic site testing equipment consisted of a meteorological station recording temperature, pressure, humidity, and wind speed and wind direction. Seeing measurements were conducted using a standardized Differential Image Motion Monitor (DIMM), while atmospheric turbulence strength as a function of height was measured with a Multi-Aperture Scintillation Sensor (MASS). Local atmospheric dust was detected with different commercial devices. Later on in the campaign it became clear, based on an extensive study of the Paranal seeing characteristics, that knowledge of the surface layer is very important. Therefore a Lunar Scintillometer (LuSci) was deployed.
Here we summarize the instruments used and the parameters derived from them. A comparison of the results for each site is given in Section 7.
WEATHER STATIONS: WIND AND HUMIDITY
Several automatic weather stations (AWS) have been in use at the various sites studied to measure wind speed and direction, air temperature, pressure and relative humidity. Wind speed sensors were installed at 10 m above the ground at the DHV site on La Palma and Ventarrones. The TMT project AWS at Armazones and Tolonchar were mounted 2m above the ground, with additional air temperature sensors installed on 30m towers.
The E-ELT Basic Reference Design states that the telescope enclosure must be closed at wind speeds above 18 m s-1, and that the telescope cannot point into the wind for wind speeds
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between 12 – 18 m s-1. The dome must also be closed for high humidity. Rather than specifying a humidity limit, the closing conditions due to humidity are specified in terms of the difference between ambient temperature Ta and dew point Td of 2.5 C. The temperature margin of 2.5 C allows for cooling of the telescope structure and variable conditions while still avoiding the risk of condensation.
SKY TRANSPARENCY
Atmospheric transmission is one of the key parameters that determine the quality of an astronomical site. At optical and near-infrared wavelengths the atmospheric transmission is, first and foremost, determined by cloud cover, and the fraction of clear nights is one of the most important parameters used in the ranking of astronomical sites.
Satellite data may be used for the evaluation and forecasting at astronomical sites (e.g. Erasmus & Sarazin, 2000). Meteorological satellites in geostationary orbits provide uninterrupted monitoring of the cloud cover, yet at low spatial resolution. Higher spatial resolution is obtained from satellites at lower orbits, yet at the disadvantage of incomplete temporal sampling. The data contained in this report were obtained from the GOES12 images in the 10.7 μm band for the Chilean sites. The GOES12 images are characterized by a spatial resolution of 5 km and are updated every 3 hours. Data for La Palma were obtained from the EUMETSAT cloud product service derived from the second generation of METEOSAT satellites which provide a higher spatial resolution of 3 km. The nocturnal cloud mask test uses the brightness temperature at 10.8 μm and the albedo at 3.9 μm to detect ice clouds, liquid water clouds, and clear scenes (Kidder et al., 2000). A night is declared ‘clear’ if there are no clouds in two subsequent GOES12 images, thus 6 hrs in a row, or if the total number of METEOSAT images when the site is clear add up to more than 4.5 hrs per night.
During clear nights, atmospheric extinction at optical and near-infrared wavelengths is mainly dominated by ozone absorption below wavelengths of 320 nm (resulting in the atmospheric cutoff) and around 600nm, by Rayleigh scattering due to atoms and molecules, and Mie scattering by aerosols (e.g. Tueg et al., 1977). Discrete telluric absorption lines arise from molecular oxygen, ozone and water molecules, and the transmission near the edges of the near- and mid-infrared atmospheric windows depends critically on the precipitable water vapour column density (Lord, 1992, see also http://www.gemini.edu/node/10781?q=node/10789 and Section 5.2 on precipitable water vapour).
TURBULENCE PROFILING: DIMM AND MASS
For seeing-limited observations, the signal-to-noise ratio scales roughly inversely proportional to the image quality that is being obtained. The image quality, generally measured in terms of the diameter of the image of a point source that encircles a certain fraction of light, is thus a fundamental parameter that determines the scientific productivity of an optical telescope. This is even more so the case for adaptive optics, where good seeing facilitates attaining high Strehl ratios, as will be crucial for the E-ELT.
DIMM and MASS measure two complementary parameters of optical turbulence. The Differential Image Motion Monitor, DIMM (Sarazin & Roddier, 1990) measures the difference in the slope of the wavefront over two pupils. The variance of the differential image motion between the sub-images is calculated and compared to the theoretical variances based on Kolmogorov turbulence to provide an estimate of the integrated seeing through the atmosphere. The Multi Aperture Scintillation Sensor, MASS (Kornilov et al., 2003), on the other hand, measures the scintillation of stars in four concentric apertures of the telescope pupil using 2 photomultipliers. The vertical Cn (h) profile in six altitude layers located at 0.5, 1, 2, 4, 8, and 16 km height is obtained from a fit to a model (Tokovinin et al., 2003). The vertical resolution of MASS is low and about 50% of the altitude in each layer. MASS is not sensitive to the turbulence in the first few hundred meters as ground layer turbulence does not produce scintillation of point sources.
The interpretation of DIMM data in terms of the image quality that can be achieved with an optical telescope requires the scaling of differential image motion over small baselines to a
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much larger telescope pupil (Tokovinin, 2002a). In the framework of the scale-free Kolmogorov model of turbulence (with infinite outer scale), and in the absence of local degradations2 the image quality obtained in seeing-limited observations equals the seeing inferred from the DIMM.
The seeing ε0 is determined by the strength of the optical turbulence, generally expressed in terms of Fried's parameter r0, with ε0 being inversely proportional to r0. The approximation of the seeing based on DIMM measurements is good for telescopes with an aperture D << L0, where L0 is the outer scale of turbulence. Values of the outer scale range from 20 – 50 m typically (Martin et al., 1998; Tokovinin et al., 2007). For telescopes with apertures that become comparable to the outer scale, von Kármán's model is needed when assessing the seeing in terms of an image quality that may be reached. For large apertures the image quality that is reached (in the absence of local degradations) is better by tens of percent than the integrated seeing ε0.
When comparing seeing measurements for different sites, it is important to cross calibrate the instruments against each other. The cross-calibration of DIMMs used for the TMT and ELT site surveys shows that the obtained seeing measurements are, in general, consistent when using different instruments for simultaneous measurements at a given site. A cross-calibration of the ELT-DS DIMM with the IACDIMM was performed in September 2007 (http://www.iac.es/site- testing/index.php?option=com_content&task=view&id=95), with both instruments located on the same spot at the ORM. Other cross-calibrations are discussed by Sarazin et al. (2008).
The seeing measurements obtained from the DIMM εDIMM and the integrated MASS seeing εMASS may be used to estimate the seeing in the ground layer εGL (Skidmore et al., 2009) as follows:
5/3 5/3 3/5 εGL = (εDIMM − εMASS) / (⏐εDIMM − εMASS ⏐) x ⏐ εDIMM − εMASS ⏐
COHERENCE TIME AND ISOPLANATIC ANGLE
The efficiency of adaptive optics and high angular resolution techniques depends on the coherence time τ0 and the isoplanatic angle θ0. The atmospheric time constant τ0 or coherence time is a critical parameter for all high-resolution techniques and in particular for adaptive optics. 2 The value is derived from the Cn (h) profile and the wind speed profile V(h) according to
− ∞ 3/5 τ = 0.057λ6/5[]C 2(h)V(h)5/3dh 0 ∫0 n
The coherence time may also be estimated from the differential-exposure scintillation index which is computed for the smallest MASS aperture as a differential index between 1 ms and 3 ms exposures (Tokovinin, 2002b) – the coherence time obtained in this way is called τMASS and is used in our analysis.
2 The isoplanatic angle θ0 is also derived from the Cn (h) profile, as follows:
− ∞ 3/5 θ = 0.057λ6/5[]C 2(h)h 5/3dh 0 ∫0 n
All other things being equal, θ0 is an indicator for the typical altitude of turbulence in the atmosphere. The isoplanatic angle varies surprisingly little between sites.
2 Mirror- and dome seeing introduced by a poor control of the thermal environment of the telescope and its enclosure; telescope tracking errors and wind shake; static aberrations from the telescope and instrument optics and collimation problems; various detector characteristics such as pixel scale, charge diffusion; etc.
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5.2 OTHER INPUT
TURBULENCE PROFILING: LUSCI
Scintillation from extended sources such as the Sun or the Moon may be used to measure the 2 Cn (h) profile at low altitudes at a high vertical resolution. Due to the extension of the source, the scintillation signal from altitudes above ~100 m is spatially averaged. Thus, a lunar scintillometer (LuSci; Hickson et al., 2004), which measures spatial correlations of the scintillation signal from the Moon, senses turbulence located mostly below 100 m (Tokovinin, 2007).
As part of its E-ELT site characterization program, ESO carried out limited LuSci observations during 2009 at Paranal, Armazones, Ventarrones, Vicuña MacKenna, Tolonchar, and near the Magic telescopes at La Palma. Unfortunately, the interpretation of the LuSci data is still problematic. A comparison with SLODAR3 data obtained simultaneously at Paranal suggests that LuSci underestimates the integrated turbulence below 500 m by a significant factor. However, a closer look at the SLODAR turbulence profile reveals it to be flat above ~70 m, rather than continuing to decrease as one would expect. Hence, an alternative interpretation is that SLODAR is measuring noise above ~70 m and, thus, overestimates the integrated turbulence below 500m. An alternative check of the LuSci data is to subtract the total turbulence measured by LuSci out to 500 m from the DIMM seeing and compare the result with the MASS measurements. Again, this test seems to indicate that LuSci underestimates the integrated turbulence. However, when only the most turbulent of the LuSci data are considered, the agreement with the MASS-DIMM measurements is much better. Using only these most turbulent data, the tentative conclusion from the LuSci observations is that the surface layer turbulence appears to be weakest at Vicuña MacKenna, Tolonchar, and Armazones, and strongest at Paranal and Ventarrones. The surface layer at the Magic site on La Palma is much more turbulent than in any of the other sites, but this is possibly a local effect due to the Magic buildings and telescopes.
PRECIPITABLE WATER VAPOUR
The integrated precipitable water vapour (PWV) in the atmosphere above a site is a critical parameter for determining performance in the mid-infrared, in particular in the Q-band. The transmission of near-infrared bands, specially the J-band, is also affected by water vapour variations. Precipitable water vapour is conventionally expressed as the amount of water (depth in mm of a vertical column of unit cross sectional area) that would be obtained if all the water vapour in a specified column of the atmosphere were condensed to liquid. In general, PWV is strongly correlated with elevation, and can exhibit strong seasonal variation. Of the sites under consideration for the E-ELT, Tolonchar has the lowest PWV (median of ~1.4 mm). Armazones and Ventarrones are also quite dry sites with a median PWV of ~2.0-2.1 mm. Due mostly to their lower elevations, Vizcachas and La Palma have the highest median PWV (~3.8 mm). For completeness we mention here the PWV values resulting from the TMT site testing study for Armazones and Tolonchar of 2.9 mm and 1.7 mm, respectively (Schöck et al., 2009).
Satellite imaging provides a good baseline for examining the long-term behaviour of PWV above candidate E-ELT sites, but these data must be carefully calibrated to allow direct comparison. Florian Kerber has led an impressive effort by ESO to calibrate the GOES data for Paranal and La Silla using high-dispersion optical spectroscopy, radiosonde launches, and 20 μm radiometers (Kerber et al., 2010). These measurements allow reliable estimates to be made from long-tiime base GOES imaging of the median and seasonal variations of the PWV at Armazones, Ventarrones, and Vizcachas. Over 8 years worth of GOES data was analysed. A similar calibration campaign for Tolonchar could not be easily realized due to the undeveloped nature of the site, but in this case an excellent alternative is to scale the extensive APEX measurements of PWV on nearby Chajnantor at 5050 m. The geography and climate of La
3 SLODAR (SLOpe Detection And Ranging) is a triangulation method, in which the turbulence profile is recovered from observations of bright binary stars using a Shack-Hartmann wavefront sensor.
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Palma significantly complicates the calibration and interpretation of satellite observations of PWV. For this site, GPS measurements by Garcia-Lorenzo et al. (2009, 2010) provide the most reliable indication of the PWV properties.
DUST
The presence of dust at a site can affect operations of the E-ELT in two aspects:
1. Dust dispersed in the atmosphere along the line-of-sight of the telescope directly affects the quality of the observations in several ways. Dust increases atmospheric absorption and decreases photometric accuracy of the measurements. It may create point image diffusion in case of particles with a relatively high ratio of forward scattering to absorption. Moreover, suspended dust increases the sky background as it scatters light arising above the dust layer, or below it (Benn & Ellison, 2007). The sky can be brightened by the zodiacal light and starlight scattering by up to a few tens of percent, but the most important contribution is the back scattering from streetlights. The increased background is significant only above Av=0.25, corresponding to about 20% of the nights at La Palma sampled by Benn & Ellison (2007). For extinction between 0.4 and 0.8 mag, the increase of the background is estimated to be about 1 mag. Furthermore, the presence of dust considerably increases the sky background by moonlight (see Krisciunas & Schaefer, 1991, for the moonlight models). Dust also has a measurable effect on polarization measurements (Bailey et al., 2008). And finally, dust scattering may affect laser operation, both for the launched beam as well as for light returning from the laser beacon.
2. Local dust can stick on the coating of mirrors, accelerating the chemical degradation of these, and increasing scattering. Furthermore, at high concentrations, dust can accumulate in the filters of the ventilation systems of electronic devices.
Airborne particle counters were used on various locations to measure the suspended dust content. At Armazones and Tolanchar, the TMT particle counters measured continuously during the years 2006, 2007 and 2008. On La Palma data was used from two devices located at the Nordic Optical Telescope and at the Telescopio Nazionale Galileo. Also for Paranal and La Silla extensive measurements are available. For Ventarrones no measurements are available. The equipment used differs between sites, and also their elevation above the ground varies, which may cause systematic differences in the measurements. In order to bring the measurements to a common scale, the particle densities are summed up to a size of 5 μm.
The Canary Islands and the Cape Verde Islands are known to be occasionally affected by a wide plume of dust originating in the Sahara desert. La Palma is the most distant from the Africa coast among the Canary Islands, but the plume is usually still thick when it reaches the island. The Sahara is the most important surface deposit of dust on Earth. Dust which affects La Palma probably originates on the Ahaggar massif in Libya (Murdin, 1986). The dust is picked up by wind (even at a low speed) and then brought at high altitude by the strong daytime convection driven by the heating of the ground. It can reach an altitude of about 7 km in summer and somewhat less in winter. A typical layer from 1 to 6 km is horizontally transported by the high- speed winds over large distances. Once the plume is formed, it reaches the Caribbean in a few days, and sometimes it crosses even the North American continent. Some 2 x 108 t per year is removed from the Sahara, with an important impact on the marine biology, as well on the ecology on the other side of the Atlantic Ocean, in particular changing the Ph of the water basins.
The dust is homogeneous, but large particles can undergo a settling process by gravity in a time scale of a day. The wind direction and intensity depend on the season and on the meteorological situation. La Palma is located on the northern boundary of the typical summer plume extended to the Atlantic. The dust reaches La Palma during June, July and August. In winter time the plume moves further south, directly over the Cape Verde Islands. There are only occasional episodes of dust over La Palma in February and March.
The principal dust component is quartz, followed by calcite and mica and some plant residuals. The particle density at La Palma decreases approximately with a power law of the size between
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0.3 and 100 μm, with 95% of the particles smaller than 100 μm. The extinction during dust storm episodes is largely dominated by the smaller particles.
Satellite imagery often detects the peaks of the highest mountains of the Canary Islands above the dust, but sometimes, in particular in summer, the upper boundary of the plume is considerably higher. From ground measurements the dust storms appear as a sudden increase of about two orders of magnitude of the local submicron dust concentration. The typical thickness of the layer above El Roque de Los Muchachos during these storms has been estimated by Lombardi et al. (2008) to be about 2-3 km. The resulting upper boundary (about 5 km from sea level) is comparable to the estimated upper limit of the boundary layer measured above the desert.
The fraction of clear nights affected by dust extinction, deduced from photometric measurements of the extinction with ground based telescopes, depends on the threshold and on the definition of a clear night. Guerrero et al. (1998) give about 25% of the summer time affected by dust assuming a limit of 0.15 mag. per airmass. In winter time it decreases to about 10%, but a significant fraction of these nights could be confused with nights affected by thin cloud extinction. The visual extinction during the dusty days is typically around 0.2 mag per airmass but it can reach up to one magnitude or more during dust storms. The absorption is typically gray in the optical and relatively uniform. The storms persist about 2-4 days in summer, only one or two days in winter.
In general there is a good correlation between the dust concentration measured at ground level and the vertical visual extinction, indicating a wide area involved. However, there are also local episodes of increased dust, correlated with wind blowing from the South, when the extinction does not significantly increase. This suggests a local phenomenon related to the edge of the Caldera.
Dust storms in the Chilean sites are very rare, and satellite images of Chile don't show the thick, wide plumes of dust typical of the African west coast. Measurements of the local dust concentrations are available for Paranal, Armazones and Tolonchar. At Paranal the dust concentration is very low, while neighbouring Armazones appears to be somewhat dustier. Since Armazones is significantly windier than Paranal, it seems likely that at least part of the excess dust may be local and due to loose dust on the ground resulting from traffic and other construction/operation related activities. In fact, the dust-rose of Armazones shows a clear correlation between wind and dust: essentially all the high dust events happen when the wind blows from the NW and is stronger than ~12 m s-1.
Tolonchar is a peculiar site, with a surprisingly high average dust concentration, from two to three times higher than La Palma (excluding dust storms). Tolonchar only rarely suffers from dust storms. The wide scale UV images from TOMS confirm the detection of a significant amount of aerosol in the area, with a peak during the southern summer, but it is not possible to get quantitative data on the thickness and height of the layer without simultaneous ground based measurements or assumptions on the optical quality of the dust particles. Photometric observations carried out in December 2009, when the dust concentration was known to be near its maximum, do not show any increased visual extinction, indicating a low altitude upper boundary above the peak of the site. The data analysis shows that at Tolonchar there is a dominant wind coming from NW, where there is significant mining activity (Salar de Atacama and Chuquicamata mines). Dust events are also observed when the wind is from the NE, in the direction of the Lascar volcano.
For the E-ELT cleanliness of the optics will be an important factor during its operational life because of the difficulty to clean the huge reflective surfaces. A single major dust event while the telescope is operational could affect scientific work for many months. Therefore suspended dust will play a more important role in the site selection process than typically has been the case for smaller telescopes. Although there is no firm engineering limit for acceptable particle densities, as a working hypothesis the limit is set at a level corresponding to an extinction of 0.2 mag in the zenith. This limit robustly distinguishes typical background dust levels from dust storm events for which one may reasonably expect the telescope will close. From a calibration of particle densities against extinction this operational limit corresponds to 19 μg m-3.
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TEMPERATURE AND SKY BRIGHTNESS
At wavelengths above 2.3 μm, the dominant parameter that determines the brightness of the sky is the temperature of the atmosphere. In the thermal infrared where most of the observing programs are background limited, the integration time needed to reach a given signal to noise ratio is proportional to the sky background. Thus, a colder site with a reduced sky background results in significant savings of observing time. At near-infrared wavelengths, the dominant contributions to the sky brightness are discrete emission lines of the OH molecule. The sky brightness (in the absence of moonlight) in the optical wavelength region is caused by airglow from the emission of atoms and molecules in the mesosphere (below 100 km), to some extent by Aurorae, and by artificial light sources and light pollution (see Section 6.1 for a discussion of light pollution). As is summarized above, the presence of dust in the atmosphere degrades the quality of a potential ELT site in various ways. Thermal emission from dust augments the near- and mid-infrared sky background, and moonlight scattered on dust augments the sky brightness at optical wavelengths.
6. OTHER CONSIDERATIONS
6.1 LIGHT POLLUTION
Light pollution is a significant concern for all existing and potential astronomical sites. Mountains that were selected for their dark sky conditions only 50 years ago (e.g., Kitt Peak) are now faced with significant encroachment from man-made sources of light. Increases in population and standards of living are conspiring to produce a growth in artificial light that is now threatening all but the most remote sites in the world. The existing level of light pollution and its potential for growth over the lifetime of the E-ELT is therefore an important additional consideration in evaluating the proposed sites. In evaluating this factor, the SSAC has employed existing observations at Paranal and La Palma, all-sky images obtained at Armazones and Tolonchar as part of the TMT site testing campaign, and calculations of the present and future sky brightness at all five candidate sites using the Garstang (1989) model. These data indicate that Armazones, Ventarrones, and Tolonchar are all very dark sites that should remain this way until 2050 and beyond as long as there is no significant increase in the surrounding mining activity. Light pollution at Vizcachas is also currently negligible, but could become a threat over the lifetime of the E-ELT depending on the level of nearby mining activity and projections of the future growth of the cities of La Serena, Coquimbo, and Vallenar. La Palma is the only E-ELT site that currently suffers a measurable light pollution amounting to 0.05-0.10 mag at the zenith (Pedani, 2004). Fortunately, most of this is produced by low- pressure sodium lamps, and is therefore confined to the Na I D lines that are naturally present in the dark sky. Future growth in tourism appears to be the largest concern for keeping light pollution at this site from growing significantly in the future.
6.2 SEISMICITY & VOLCANIC ACTIVITY
The E-ELT sites in Chile are located in an area of strong seismic activity, whereas La Palma has no significant history of seismicity. The recent 8.8 magnitude earthquake in southern Chile serves to emphasize that seismic activity poses a significant risk if the E-ELT is sited in Chile. ESO has considerable experience in earthquake risk analysis and engineering, particularly in the context of its installations on Paranal. The E-ELT project office is adopting industry norms for dealing with earthquakes and is keeping up to date with the evolution of the field by engaging leading experts. The telescope and enclosure are being designed to withstand with zero damage an earthquake that produces a peak ground acceleration of 0.24 g. In the Paranal area, such a quake has a 10% chance of occurring in 50 years. For the maximum likely earthquake condition of 0.34 g which has a ~5% chance of occurrence in 50 years, the facility is designed to incur no significant damage, meaning that it would take no longer than a month to repair any problems. Nevertheless, seismology is a probabilistic field, and so definitive answers
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for what may actually occur over the lifetime of the E-ELT if it is sited in Chile cannot be given. The SSAC notes that the additional stiffness required for the enclosure to withstand earthquakes in Chile is roughly the same as is necessary to deal with maximum peak snow loads in La Palma. Also, the high stiffness of the telescope that is beneficial for the non-coupling to earthquakes is essential for optimal performance under wind load conditions.
Tolonchar is located 68 km to the southwest of Volcán Lascar, the most active volcano of the northern Chilean Andes. Frequent small-to-moderate explosive eruptions have been recorded from Lascar since the mid-19th century, along with periodic larger eruptions that produced ash- fall hundreds of kilometers away from the volcano. The largest historical eruption of Lascar took place in 1993, producing pyroclastic flows to 8.5 km northwest of the summit and ash-fall in Buenos Aires. Tolonchar is sufficiently far from Lascar that the most significant hazard posed by the volcano is ash-fall. Although the plume and ash-fall during the 1993 eruption was predominantly to the east-southeast of the volcano (Gardeweg, 1996), temporary changes in the wind direction could result in Tolonchar being affected by fine ash-fall in a future eruption.
Volcanic activity is also present to a lesser extent at La Palma. In the last 500 years there have been seven eruptions in the southern part of the island, the last being in 1971. These were characterized by mild explosive activity and lava flows that, in several cases, reached the sea.
6.3 CONTRAILS
Aircraft spend most of their time in the tropopause, the narrow band in the atmosphere where ice clouds typically form. Airplane exhaust plumes contain to a large extent water vapor and solid particles (mainly soot and sulfates). Under certain conditions, the particles act as condensation points for the formation of ice crystals, and the resulting contrails may persist for several hours. Contrails are one of the most visible anthropogenic effects on the atmosphere and may affect future ground based astronomical observations. The potential for contrail formation is thus of relevance for the ELT site search.
Contrail formation over the Canary observatories is rare. A 38 nautical mile exclusion zone for the ORM seems sufficient, and contrail formation only occurs during conditions that are not suitable for astronomical observations. In the north Chilean area regular air traffic is present, both for short-distance national flights as for intercontinental flights, but the traffic is currently not intense.
Predictions of persistent contrail formation for 2050 based on assumed air traffic growth rates are available in Saussen et al. (1998). The scenarios developed in that study are generally alarming, but the qualitative view is that for all of the potential ELT sites persistent contrail formation may become a nuisance by the year 2050.4
6.4 THE SODIUM LAYER
Adaptive optics, and hence the use of laser guide stars is of critical importance to the E-ELT. The most appropriate way to create artificial point-like sources in the sky for wavefront sensing is through resonant fluorescent back scattering of laser light off the mesospheric sodium layer that is found at a typical height of 95 km. The density of this sodium layer, its height and temporal variations impact on the design of the laser system and adaptive optics instrumentation and is therefore relevant for the selection of the site for the E-ELT.
Various experiments have been conducted to monitor the strength and behavior of the mesospheric sodium layer at, or close to the potential E-ELT sites (e.g. Ageorges & Hubin, 2000; Michaille et al., 2001; d’Orgeville et al., 2003; Chueca et al., 2004; Ageorges & Els, 2004; Roberts et al., 2007). Seasonal variations, nocturnal changes and sporadic events are
4 We gratefully acknowledge discussions with H. Pedersen from the Niels-Bohr Institute in Copenhagen.
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commonly observed. Reported sodium column densities are typically a few times 109 cm-2 both in Chile and La Palma. Sodium abundances tend to peak in winter, with peak values two to three times their summer values. There exists also a dependence on the geomagnetic field of the photon return from the sodium layer (Moussaoui et al., 2009), but for the sites considered here that have a similar distance to the geomagnetic equator this does not pose an important distinguishing factor.
In conclusion, the sodium layer appears to present similarly valid conditions for the use of laser beacons at all the potential E-ELT sites.
6.5 LONG-TERM CLIMATE CHANGE
The operation of the E-ELT is foreseen to last several decades. As a consequence, a complete evaluation of the E-ELT sites properties cannot ignore climatic changes on this time scale. Considering that the Chilean sites are located in a latitude range between 23º and 33º S, and La Palma at 28° N, all belong to the subtropical belts that are influenced by a comparable wide- scale atmospheric regime, characterized by the subsiding branch of the subtropical Hadley cell. However the geological and climatic histories of these sites are rather different, as is the local meteorology.
THE CHILEAN SITES
The prediction of the climatic trends in the Chilean sites is a difficult problem because little is known about the Atacama Desert, and specifically about the Andean and pre-cordillera area south of 23º S, due to the relatively short duration of systematic meteorological measurements. In addition, the potential sites are distributed in non-populated areas where there are no historical records.
The Atacama Desert is a geologically young feature, appearing about 12 Myr ago when the uplift of the Andes progressively reduced the zonal circulation at low altitudes. Evidence of this change is found in the ceasing of erosion and canyon cutting about 5.3 Myr ago. At the same time, in the Pacific Ocean, the Humboldt current increased its influence, while the corresponding counter-running warm current retreated. The extremely arid condition of the Atacama region was reached more recently, about 10.000 years ago, after the last glaciation.
The current climatic conditions over the Atacama Desert have been summarized by Fuenzalida (1983) and by Grenon (1990). The wet, tropical air masses are now blocked east of the Andes for most of the year, but during the southern summer they may cross the Andes and invade the western side due to movement of the Pacific anticyclone to the south. This period is referred to as the “Bolivian” or “Altiplanic” winter: the humid air masses may give rise to precipitations at high altitude, but when they reach low altitudes the relative humidity is typically lower than 30%. The storms coming from the west side are usually stopped by the anticyclone at latitudes lower than about 25º S year round. The coastal cordillera limits the influence of maritime humidity to a narrow strip along the coast. The precipitation regime up to 4000 m altitude is quite regular, with storms concentrated between November and April and more pronounced near the Chilean border. The dry desert ends around 27º S. At more southern latitudes, the weather is characterized by invasions of fronts coming from the polar regions, which happens more frequently during the southern winter when the anticyclone shifts to the North. At La Silla the pronounced decrease of photometric nights in winter is caused by this polar front activity.
As already pointed out, the restricted time range of the meteorological measurements is a major limitation for studying the long-term climatic trends in this area. Grenon (1990) reported the analysis of the hydrograms of Rio Huasco and Rio Carmen, monitored from 1942-1986, as climatic indicators for La Silla and Las Campanas. There is evidence of severe winter conditions with almost periodic 7 or 12 years variability. It is interesting to note that the site campaign performed in the years 1961-1962, when La Silla site was chosen, corresponds to a stable dry period. The limits of the desert region, and therefore the stability of the conditions in the Paranal area, are sensitive to global temperature changes. The transition region, nowadays located around 26-27º S, is most sensitive to climatic change. It is expected that temperature increases
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would shift the southern limits further towards the South, while a cooling would move the limit progressively to the North and precipitation in the La Serena region would be expected to increase. From a vegetation study the latitudinal shift of the climate during the last ice age was about 7 degrees. It has been speculated that the climatic conditions at Paranal were similar to those currently present at La Silla. Actually (in the period 1985-2007) the temperature at Paranal shows an increasing trend of about 0.4 C per 10 years (Lombardi et al., 2009) vs. a global warming estimated around 0.7 C per 10 years. In the same period the pressure did not significantly change.
The conclusion of this analysis is that, while the subtropical conditions are considered among the most variable on the Earth, the area around Paranal, located well inside the Atacama dry desert, should be considered quite stable in a global warming scenario. This is confirmed in the wide scale models of the 2007 Intergovernmental Panel on Climate Change report (http://ipcc- wg1.ucar.edu/wg1/Report/AR4WG1_Print_SPM.pdf). The projected patterns of precipitation changes for the period 2090-2099, relative to 1980-1999, show a negligible variation.
Intra-seasonal and inter-annual rainfall and moisture variability have been studied in detail by Garreau (2000) and Garreau & Aceituno (2001). They limited the study to the region just to the north of Paranal, between 15º and 21º S in the Altiplano, at an average altitude of 3800 m. In this region the Bolivian winter regime is prominent, with rain episodes during summer concentrated in periods of almost one week.
On interannual timescales, the Altiplano rainfall experiences strong fluctuations. The summertime weather variability, mostly the number of days characterized by an easterly flux of wet air, dominates the inter-annual variability. El Niño events are considered associated with westerly anomalous conditions giving dry conditions over the Altiplano. However, rainfall anomalies are tightly dependent on the location of the zonal wind anomalies, with the conclusion that the predictions in this region require detailed knowledge of the small-scale structure of the subtropical circulation.
Data collected from TOMS satellite archives in the last 30 years (Bertolin, 2010), based on the mean UV reflectivity, confirm the stability of the climate at La Silla, Paranal and Tolonchar. La Silla presents the highest yearly variations in cloudiness, with an almost regular periodicity of about 3-4 years but no evidence of a systematic trend in the last two decades appears from the data. Nevertheless, a systematic trend is apparent in the ground-based data derived from Paranal and La Silla telescopes logbooks. Starting from 1983 the difference of the photometric nights fraction at Paranal compared to La Silla decreased from about 30% to almost zero after 2003. While the absolute ratio could be affected by a different judgement in the two sites, there is no obvious explanation of this change. If we exclude a bias in the data, an obvious interpretation could be the atmospheric circulation (in particular the Bolivian high) moving South, possibly connected to some El Niño events (Sarazin, 1997). However, the pressure measured at Paranal (Lombardi et al., 2009) doesn't show any relevant change, above the instrumentation errors, from 1985 to 2007. The context of this change is not obvious in the long-term theoretical evolutionary models and appears more as a temporary event.
A complete discussion on the climatic trends in Chile cannot ignore the presence of El Niño, a semi-periodic wide-scale event with pronounced climatic effects on the meteorology of northern Chile. A full discussion goes well beyond the scope of this status report. Here we limit ourselves to the fact that although the El Niño events appear to have an effect on the number of photometric nights at La Silla (Sarazin, 1997), at Paranal the correlation is not so clear. Moreover, how the El Niño events will develop in the future remains a point of debate.
In conclusion, there is no evidence for dramatic climate changes for the relevant areas in northern Chile on the time scale of some decades. However, long-term climate forecasts in the specific selected sites remain limited.
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LA PALMA
La Palma is located at a latitude of approximately 28º N, several hundred km off the west coast of Africa in the Azores high-pressure system. In this region the meteorological situation is very stable, dominated by the trade wind system with a direction dependent on the altitude, and rotating from NE at sea level to N at the inversion layer altitude, and finally to NW above the height of the observatory. Below 1000 m, these winds transport cold air masses from higher latitudes. According to the direction of the wind, the surface ocean current (Canary stream) brings cold water from the north. The mean sea temperature at Canary Islands is about 22 C in summer and 18 C in winter, well below the average temperature at this latitude. This cold stream stabilizes the air layers. Between 1200 and 1600 m altitude, there is a strong temperature inversion layer of about 4 C degrees separating the lower convection from the subsiding air masses coming from the general tropical circulation (Hadley cell). The high pressure guarantees the stability of the inversion layer mostly during the summer. In winter the storms can reach the island and break the inversion layer causing an increase of humidity at the site.
The IPCC models (2007) do not indicate significant wide scale variations in the region of the Canary Islands from now until the 2090-2099 period.
There are few specific studies on La Palma climatic trends. A summary is presented by Graham (2002) in the ESPAS report available at http://www.vt-2004.org/gen-fac/pubs/astclim/espas/ espas_lib.html. Lombardi et al. (2006, 2007, 2008, 2009) discuss the temperature, precipitations, wind and pressure records, while Moulin and Chiapello (2004) and Chiapello and Moulin (2002) present the study of the variability of the African dust transport over the Atlantic. The yearly temperature variations at La Palma, starting from 1971 (Graham, 2002) have been interpreted as consequences of the Northern Atlantic Oscillation (NAO) measured as pressure difference between Iceland and the Azores. Increasing NAO means enhanced westerly flow, which brings cooler air while with negative NAO there is some increase of anomalous meridianal flows. Superimposed on this oscillation there is a long term warming of about 1 C over the past 30 years (1 C over only 10 years is reported in Lombardi et al., 2009). These numbers are considerably higher than the global warming. There is, however, no evidence of correlation between the average yearly temperature and the observing conditions. The pressure appears not to have significantly changed in the last two decades: a limited increasing trend of 2 hPa, from 1985 to 2007 is at the limit of the instrumental accuracy.
Annual precipitation has been highly variable in the thirty-year period from 1971 to 2000, but there is no clear long-term trend. There is some correlation of the precipitations with NAO. Very strong positive periods of NAO coincide with very dry phases, for example in 1990 and 1999- 2000. There are indications of an increased variability after 1987 coinciding with a similar variability increase of NAO. The inter-annual variability of the desert dust transport over La Palma has been studied mostly from TOMS satellites starting in 1979 with the Nimbus 7. There are wide variations of the mean optical thickness in the area, but no clear trends in the last three decades. The correlations with the NAO and other indices (for example the Sahel Drought index) are not very clear because of the dependence of the high altitude dust transport efficiency on several effects, including the wide scale wind speed and direction, the convection efficiency over the desert areas, or the humidity at ground. Furthermore these effects should not be simultaneous. For example, exasperated dry conditions in the Sahel index could anticipate major dust storms of the following year. In fact, the previous year Sahel drought index and the dust optical thickness over the ocean are quite well correlated. The wide scale NAO oscillations appear not to be well correlated on a yearly base with the optical thickness but a clear positive correlation appears when the comparison is limited to the winter (December-March). A recent analysis of dust measurements on Tenerife over five decades confirms the absence of any clear trend (Cuevas et al., 2009).
The conclusion is that there are no defined decadal trends for La Palma directly connected with the observations.
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6.6 OPERATIONAL SYNERGIES
For the E-ELT to be located at a short distance from one of ESO’s operational locations has various potentially attractive aspects. Facilities for which major investments have been made on Paranal are probably also of use to the E-ELT and would avoid duplication of infrastructure, maintenance, and support staff. Infrastructure may need to be expanded on Paranal to support E-ELT-specific activities and to allow expansion of personnel on site, but this is probably more cost effective than setting up on a new site. Clearly the effectiveness of such synergies decreases with distance.
An aspect that is not so easy quantifiable but will undoubtedly be important is the engagement of ESO staff at all levels with this grand new project. A coordinated approach to running Paranal and the E-ELT will strengthen the observatory as a whole and facilitate optimal use of the available human resources.
As examples for possible synergies with Paranal we list:
• The control room of the E-ELT could be in the actual VLT Control Room • Re-use of parts of the coating infrastructure is possible • The Paranal residencia, canteen, medivac facility, workshops, warehouses, recreational and sports facilities could be shared or extended • The existing power generation system at Paranal could be expanded and power lines run to Armazones • LN2 plant production and garbage disposal could be shared • The existing radio communication infrastructure at Paranal could be expanded • Vehicles could be fueled at the existing gas station at Paranal
Many of these synergies are shared by Ventarrones, although the increased distance of this site from Paranal makes the advantages somewhat less.
Vizcachas is located only a short distance from La Silla, and so all of the above operational synergies for Armazones and Ventarrones apply also to this site.
Apart from some minor commonalities with ALMA and Paranal, the relatively isolated location of Tolonchar means that there are no significant operational synergies for this site.
On La Palma the E-ELT would be erected among several other telescopes at the Observatorio del Roque de los Muchachos, which hosts a considerable infrastructure and common services that could be also of benefit to the E-ELT. The SSAC was informed that there is an offer from the Spanish government that the following facilities could be made available or shared with others:
• Residencia and canteen • Power supply • Water supply • Gasoline supply • Communications • Garbage disposal • First Aid • Access roads • Heliport
We note that parts of the infrastructure (e.g. Residencia, power supply, water supply) would require very substantial upgrades in order to accommodate the E-ELT. Although the E-ELT on La Palma would be a new location for ESO, very remote from its other observatories, the presence of a modern observatory does provide opportunities for access to specialist knowledge and experience locally.
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6.7 CONSTRUCTION & OPERATIONS COSTS
A detailed assessment for three different locations was carried out by ESO in order to identify potential difficulties that could be encountered at the time of constructing the facility, and to quantify the cost differentials for construction and for the operational phase (Tamai, 2009). The three sites were: Armazones, Tolonchar, and La Palma. These sites were chosen so as to contrast a location close to an existing ESO observatory, a very high site, and an island site within an existing observatory. This comparison was considered to be representative for the other sites as well.
The aspects that were considered relevant for the construction and operation include: the space requirements, geological aspects (including earthquake risks), platform preparation, altitude, meteorological aspects, power requirements, fuel and water availability, access to the site, accommodation and transport, permits for environmental aspects and for laser operation, synergies with nearby facilities, staff costs, and availability of local skills and services. No showstoppers were found for any of the sites, but there are clearly local differences, which have a cost implication.
The result of this study identifies Armazones as the least expensive site for both construction and operation of the E-ELT. Taking this site as the benchmark, construction on Tolonchar would be 53 M€ more expensive, while construction on La Palma would be about 25 M€ more costly. Considering the total cost of the project the committee believes that although the higher construction cost for Tolonchar and La Palma is significant, the differences are not so large that they should affect the decision on the final location.
The annual operational cost estimates show that Tolonchar is expected to be 5.5 M€ per year more expensive than Armazones, while La Palma would be approximately 2.15 M€ per year more expensive. These figures are significant in relation to the anticipated operational cost. Moreover, when also taking into account the potential savings that could come out of the operational synergy between Armazones and the Paranal Observatory, the cost differentials would be even some 1 to 3 M€ per year higher, depending on the level of coordination achieved.
The items that contribute most to the operational cost differentials are related to staff cost and the higher cost of goods and services on La Palma. The cost of electrical power is significantly lower on La Palma thanks to its connection to the power grid, while the model for the Chilean sites is based on local power generation. We note that the assessment is based on current costs and does not make any prediction about future developments of the market.
7. RESULTS
7.1 SUMMARY OF KEY PARAMENTERS
The vast volume of data collected over years is condensed in the following summary Table 1 which intends to provide the key aspects that distinguish the sites from the perspective of their astronomical use. All parameters shown refer to median night time values. In order to indicate the relevance of differences between sites, where possible we list the approximate range of values from the monthly medians. This range reflects either seasonal variation or just the representative range of the data points where there is no seasonal trend. The full volume of data is reported elsewhere (Melnick & Monnet, 2010; Melnick et al., 2010).
Some caution must be used in interpreting the data in this table. An effort has been made to obtain data with identical instruments on all sites, but in practice there are differences in many details. Although this complicates the interpretation, care has been taken to cross-calibrate instruments and measuring methods in order to allow objective comparison between all sites. Furthermore, there exist dependencies between parameters that are not obvious from the table but have been analysed and were taken into account in the detailed analysis.
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Table 1- Key site testing parameters; presented are night-time median values and where relevant the (approximate) range of values based on monthly average figures are indicated.
Parameter Armazones Tolonchar Ventarrones Vizcachas La Palma
A- Dome open clear nights 73 % 63 % 75 % 67 % 57 % B- Dome open usable time 89 % 80 % 91 % 84 % 72 % 9 2 12 13 18 C- Temperature [C] 6.7 4 -1.5 -5 10.6 9 11.4 8 7.6 2 -1 10 6 9 6 10 D- Wind speed [m s ] 6.5 4 3.2 1 6.3 4 3.9 2 7.8 5 E- Wind speed usable time 97 % 100 % 99 % 100 % 96 % F- Relative humidity 22 % 33 % 13 % 39 % 21 % G- Dew point usable time 99 % 96 % 99 % 98 % 87 % H- Dust usable time 99 % 97 % 100 % 100 % 89 % I- PWV [mm] 2.04 1.43 2.24 3.89 3.79 J- Good mid-IR time 49 % 62 % 42 % 24 % 21 % 0.8 0.75 1.1 1.0 1.5 K- DIMM seeing [″] 0.66 0.6 0.64 0.55 0.91 0.7 0.81 0.75 0.71 0.6 0.5 0.5 0.7 0.7 0.6 L- MASS seeing [″] 0.38 0.3 0.44 0.37 0.55 0.4 0.47 0.35 0.32 0.25 8 10 5 8 12 M- Coherence time [ms] 4.65 2 3.82 3 3.23 2 3.47 2 6.59 2 2.7 2.3 2.4 2.3 2.3 N- Isoplanatic angle [″] 2.35 1.8 1.89 1.5 1.87 1.6 1.83 1.4 1.88 1.5
A. Fraction of nights that the E-ELT dome may be opened and the sky is clear (cloudless) during the full night. This measure includes down time due to wind, humidity and dust. A night is declared clear if, based on satellite data, during at least 6 hours at night there are no clouds (for La Palma the threshold used is 4.5 hours, as different satellite data was employed; increasing the threshold to 6 hours would reduce the clear time percentage by about 6%; See Section 5.1). B. Fraction of time that the E-ELT dome may be opened and the conditions are usable for science. These figures are based on operational statistics from nearby existing observatories, or in the case of Tolonchar and Armazones on a combination of data from satellites and the TMT all-sky imager, scaled to the operational threshold for the E-ELT for wind and humidity, but not taking into account the dust threshold. C. Temperature in C of the air at night: median and typical seasonal variation. D. Wind speed in m s-1 at night: median and typical seasonal variation. E. Fraction of time with wind speed below the E-ELT operational threshold of 18 m s-1. F. Relative humidity at night: median. G. Fraction of time at night that the ambient temperature is 2.5 C above the dew point temperature (see Section 5.1). H. Fraction of time when the atmospheric density of dust particles up to sizes of 5 μm is below 19 μg m-3. This limit corresponds to dust events on La Palma where the extinction exceeds 0.2 mag at the zenith. This threshold is used as an estimated operational limit for the E- ELT, but is not based on rigorous engineering models. I. Precipitable water vapour in mm: median and typical seasonal variation (see Section 5.2). J. Fraction of time when PWV is below a threshold of 2mm. K. DIMM seeing: median and typical seasonal variation. This represents the full atmosphere seeing. L. MASS seeing: median and typical seasonal variation. The MASS instrument is insensitive to layers well below 500 meters. The difference with the DIMM seeing value is an indicator of the strength of the ground-layer turbulence (see Section 5.1). M. MASS coherence time in ms: median and typical seasonal variation (see Section 5.1). N. MASS isoplanatic angle in arc seconds: median and typical seasonal variation (see Section 5.1).
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Finally, in the case of La Palma there exists a bias in the MASS and DIMM data due to the very sparse data collected during the winter period, specifically during the months of December through March (the months of October, November and April are also poorly sampled, but not so extremely). In order to improve the statistics and understand the bias as a result of the sampling, the site-testing group from the IAC kindly provided DIMM data from previous years (2002, and 2005-06; note that the instrument was different from the one used for the E-ELT campaign, which could introduce small systematic effects in the seeing measurement). The combined dataset still suffers from a bias is favour of the summer months, but now with reasonable sampling of the winter months. Giving equal weight to the median seeing for each month results in a year-round average seeing value of 0.80″, which is significantly higher than the value of 0.71″ listed for La Palma in Table 1. This difference can be understood from the bias towards summer, as the median seeing over the four months of December through March is 0.94″ while the median for the remaining months is 0.72″. A similar bias is probably present in the MASS data, but this cannot be verified since there is no historic MASS data available.
Apart from the quantitative parameters shown above we also summarize our assessment of other important aspects affecting the final choice of site. The result is presented in Table 2 where we distinguish between the site having a clear advantage in the aspect considered (green), whether there is reason for concern (yellow), or whether there is a clear disadvantage (red). Here we merely present our overall assessment, while each aspect is discussed in more detail elsewhere in this report.
Table 2- Assessment of non-quantitative aspects for each site, where green indicates an advantage or positive situation, yellow a reason for concern, and red signals a clear disadvantage.
Armazones Tolonchar Ventarrones Vizcachas PalmaLa Seismicity (Sect. 6.2) Light pollution (incl. future risk; Sect. 6.1) Snow & ice (Sect. 7.2) Science synergy (Sect .4.2) Operational synergy with Paranal (Sect. 6.6) Availability of site (Sect. 7.2) Operating cost per usable night (Sect. 6.7)
7.2 SITE DESCRIPTION
Of the five pre-selected sites, three are located in northern Chile (of which two are in the vicinity of Paranal Observatory), one site is located close to the La Silla Observatory, and the fifth site is located on the Canary island of La Palma, at the Roque de los Muchachos Observatory. The following images show the location of the northern Chilean sites in their geographical context.
24 Annex 1 to Cou-1296 conf.: SSAC Status Report E-ELT Site Selection Advisory Committee – Status Report, March 2010 – CONFIDENTIAL
Figure 1- Left: General overview of the location of the candidate sites in northern Chile. Right: Close-up of the Paranal area with the main relevant mountains indicated.
We highlight key aspects of each site, starting with the Chilean sites.
The Chilean sites have a number of characteristics in common: obviously access to the full southern hemisphere is guaranteed and they therefore provide excellent scientific synergies with other major scientific facilities such as the VLT, ALMA, and the future SKA to which European astronomers have access, as well as major large scale survey telescopes such as VISTA, the VST and the future LSST. All sites in Chile also share a very high risk of suffering a major earthquake as well as possible effects from micro seismicity.
ARMAZONES
Long 70° 11′ 30″ W; Lat 24° 34′ 50″ S; elevation 3064 m (see Figure 2) The Armazones site is on top of a steep mountain without vegetation. It is well documented and tested with a long baseline of site testing information going back to the VLT site testing days. The MASS and DIMM seeing is excellent, and so is the fraction of useful nights. With respect to dust, humidity, wind and typical temperatures, it provides very good conditions for scientific operation. Its relatively low PWV makes it a good site for mid-IR observations. The proximity of Paranal provides excellent opportunities for operational synergy with the VLT and simplifies the bureaucratic processes. Skies are dark and given the distance to Antofagasta there is little risk of light pollution in the future. The steepness of the terrain implies that the mountain will have to be cut several meters, which could impact negatively on the surface layer turbulence.
Figure 2- Left: The Armazones site. Right: The Ventarrones site. Areas shown are about 13 by 9 km.
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VENTARRONES
Long 70° 12′ 30″ W; Lat 24° 24′ 10″ S; elevation 2837 m (see Figure 2) This ridge-shaped mountain top without vegetation is characterized by relatively mediocre DIMM seeing, and suffers from a strong turbulent ground layer and a relatively poor coherence time when compared to the other sites. The fraction of useful nights is, however, excellent, and skies are dark. The shorter distance to Antofagasta implies a somewhat higher, but still acceptably low risk for future light pollution. The low PWV makes this a good site for mid-IR observations. The proximity to Paranal probably simplifies the bureaucratic process to develop a new site and facilitates operational synergy with the VLT.
TOLONCHAR
Long 67° 58′ 30″ W; Lat 23° 56′ 10″ S; elevation 4480 m (see Figure 3) This mountain is high and steep, although the summit is relatively flat and without vegetation. The excellent MASS seeing conditions, low PWV, and generally low wind speed make it an excellent observing site, also for mid-IR observations. The fraction of usable nights is good, but the site suffers from occasional high clouds over the Andes mountains. The incidence of suspended dust is also relatively high compared to the other sites in Chile. Skies are very dark and there is little risk of light pollution for the future. Its high elevation implies relatively high cost for development and operation. Moreover, opening a new observatory location comes with a complex bureaucratic process, while local sensitivities require a respectful approach. Finally, Tolonchar is located near an active volcano, which could affect scientific operation in case of eruption.
Figure 3- Left: The Tolonchar site. Right: The Vizcachas site, close to the La Silla Observatory. Areas shown are about 13 by 9 km.
VIZCACHAS
Long 70° 41′ 40″ W; Lat 29° 17′ 10″ S; elevation 2389 m (see Figure 3) This ridge mountain with very little vegetation is located within the ESO territory, not far from La Silla Observatory. Hence, there is significant infrastructure and a long history of site testing data available. A relatively large fraction of time is lost to poor weather conditions, with strong seasonal variations, although observing statistics kept at La Silla reveal a slow but steady increase in the percentage of photometric nights since the mid-1980s. The site enjoys reasonably good seeing conditions, but probably not of the standard required for the E-ELT. PWV levels are high compared to the other Chilean sites, making Vizcachas less suitable for mid-IR observations. Finally, strong growth of the La Serena, Coquimbo, and Vallenar populations could increase the currently low levels of light pollution.
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LA PALMA
Long 17° 53′ 30″ W; Lat 28° 45′ 00″ N; elevation 2396 m (see Figure 4) The summit of La Palma with its light vegetation is the home of the Roque de los Muchachos Observatory. The steep mountain abruptly drops nearly vertically towards the south into the Caldera de Taburiente national park. The existing observatory offers extensive infrastructure and obviously provides complete access to the northern skies. The island has a population of approximately 85,000 inhabitants and is a touristic destination. Further touristic developments are planned on the island. This location enjoys the best median MASS seeing and longest turbulence coherence times of the five sites (but with the caveat that the data suffers from poor sampling during the winter months; see Section 7.1). Moreover, the exact location for construction of the E-ELT has not yet been established, which complicates the site selection process. La Palma has a relatively large fraction of time lost to poor weather conditions, in particular during the winter months when significant snowfall and ice formation can occur. Atmospheric dust levels show occasional strong dust storms coming from the Sahara. Typical PWV levels are high compared to the northern Chilean sites, with strong seasonal variation, making the site less suitable for mid-IR observations. There is a risk of light pollution, although the current situation still appears acceptable. In contrast with the Chilean sites there is no risk of significant seismic events. The presence of nearby forest and shrubs covering the mountain top pose a fire risk, as is confirmed by recent history.
Figure 4- Left: The island on La Palma. Right: close-up of the location of the observatory on La Palma. Area shown is about 13 by 9 km. The DHV site where most of the E-ELT site characterization data was taken is indicated; the asterisks show the two potential locations for the E-ELT.
8. DISCUSSION
8.1 COMPARISON OF MOST RELEVANT PARAMETERS
From the main site parameters, one can in principle derive figures of merit, defined as the time required to achieve a given signal-to-noise ratio. The sensitivity of the figure of merit to these parameters varies with the observing modes (described in section 4.1): while the dependence on dome-open time is the same for all modes, the sensitivity of the various adaptive optics modes clearly depends on the various turbulence parameters, seeing, vertical distribution, etc. Similarly, the sensitivity of the figure of merit to the PWV parameter is minor at optical wavelengths but critical at mid-IR wavelengths.
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Deriving a figure of merit that would encompass all parameters and all observing modes is a difficult endeavour which would require a detailed knowledge and modelling of the telescope and instrument response to these parameters. For instance, the performance of a wide-field AO instrument relates to the vertical distribution of the turbulence, its coherence time, etc., but also to the parameters of the AO system itself (number of actuators, control loop bandwidth, etc.). It is therefore almost intrinsically impossible to derive a figure of merit based purely on site parameters, in particular when adaptive optics is involved. Telescope and instrument specifications can to some extent be adjusted to the site parameters, when known. This is why three reference sites – Paranal, La Palma and Vizcachas – have been used so far when designing and specifying several of the E-ELT systems (see Section 3.2). Also, as time passes and technology evolves, technical solutions can be implemented that will smooth the dependency of the figure of merit with those site parameters that have a direct technological counterpart (e.g. ro vs. number of actuators for the AO modes).
The dome-open clear time and dome-open usable time fractions reported in Table 1 fold directly into the figure of merit, irrespective of the observing mode and of any telescope parameter (nothing can help observing through clouds). The relative merits of the sites are indicated in Table 3, normalized to the best site in our list. The figure of merit related to PWV and temperature can also be folded in directly into the figure of merit at mid-IR wavelengths, via some modelling of the atmospheric behaviour with these parameters. The results are indicated in Table 3.
The next obvious parameters affecting the figure of merit are those related to turbulence: integrated seeing, vertical distribution and in particular relative strengths of the surface, ground and high altitude layers, coherence time, outer scale of turbulence, etc. Since not all these parameters are precisely known (e.g. outer scale, surface layer turbulence) deriving a merit from the various atmospheric turbulence parameters is more complex and therefore rather tentative. Moreover, as mentioned above, the impact of these parameters can be somewhat mitigated by the choice of appropriate technical solutions. In spite of these difficulties, Melnick & Monnet (2010) have attempted to calculate the observing efficiency for the different regimes of image quality, ranging from seeing-limited observations to extreme adaptive optics. The resulting efficiencies, weighted with the projected importance of each mode as dictated by the science cases yields again a merit figure for each site. These are also indicated in Table 3. In spite of the tentative character of this exercise, the outcome identifies Armazones, Tolonchar and La Palma as equally good is this aspect, while the other two sites are clearly less attractive. This result agrees with what one might expect simply based on the median DIMM and MASS seeing values in Table 1 (we note again here the bias of the La Palma seeing data towards the better summer months). While the integrated seeing in La Palma is higher than on the two other sites, the free seeing at high altitude is the lowest, and the coherence time is the longest, hence balancing the overall merit of this site for this particular aspect. Ventarrones and Vizcachas have somewhat poorer general turbulence properties and their relative merits are less compared to the three other sites.
The figure of merit tries to capture a global picture, but the interpretation can be complicated by inter-dependencies of the different parameters. An example is the turbulence coherence timescale τ0 which on La Palma (again ignoring the bias in the data towards the better summer conditions) gives the best median value of 6.59 ms. The median τ0 for Armazones is 4.65 ms, but based on the cumulative statistics on this site τ0 exceeds the La Palma median value 34% of the time. This folded in with the clear nights statistics implies that La Palma would offer 103 clear nights with above-median values of τ0 against 90 nights above the same threshold, for Armazones.
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Table 3- Figure of merit of the various sites for some site parameters. The mid-IR figure of merit is valid in the M, N and Q bands where the thermal background from the atmosphere (and telescope) dominates.
Parameter Armazones Tolonchar Ventarrones Vizcachas La Palma
Dome open clear time, 0.97 0.84 1.0 0.89 0.75 relative to best Dome open usable time, 0.98 0.88 1.0 0.92 0.79 relative to best a) Mid-IR merit, relative to best 0.73 1.0 0.63 0.55 0.63
Seeing merit, relative to 1.0 0.99 0.80 0.84 1.0 b) best a) These figures do not include the time lost to conditions that are too dusty to observe. See Section 7.1 for details. b) The seeing merit figure for La Palma is based solely on the E-ELT site testing data, which is affected by a known bias towards the better summer months. See Section 7.1 for an assessment of this bias.
A more detailed analysis of the figure of merit may be provided in a subsequent release of this report, including more parameters. However, based on common sense, it is unlikely that the relative merits of the various sites could be significantly modified: on good astronomical sites with good seeing statistics, the prevailing parameters are the fraction of clear weather and sky transparency.
8.2 THE TIME DOMAIN
The optimal E-ELT site balances observing conditions in such a way that it gives the best opportunities to complete the science programmes that are anticipated. Stability of conditions over a timescale of a typical observing block will influence the overall effectiveness and efficiency of the facility as observations will not have to be interrupted and repeated, and the minimum of time is lost for changes in observing modes. The vast site-testing database of observing conditions has been used by Melnick & Monnet (2010) to model how well the site characteristics and their temporal development fits the anticipated E-ELT science. Although this study is still work-in-progress, the first results indicate that Tolonchar and Armazones are the best amongst the five sites considered.
8.3 COMPARISON WITH THE TMT & GMT SITES AND PARANAL
The sites of the two other ELT projects have already been decided. The TMT (Thirty Meter Telescope) project has selected the 13N site at Mauna Kea, Hawaii, and the GMT (Giant Magellan Telescope) will be located at Campanas Peak at the Las Campanas Observatory. Mauna Kea 13N lies at an elevation of 4050 m, and is located at longitude 155° 28’ 52” W and latitude 19° 49’ 59” N. Campanas Peak has an elevation of 2525 m, and is in the southern hemisphere at 70° 41’ 01” W and latitude 29° 02’ 52” S. It is interesting to compare the properties of these two sites with the five proposed E-ELT sites. Table 4 summarizes the key parameters in the same format as Table 1. The Mauna Kea measurements are taken from Schöck et al. (2009) and Skidmore et al. (2009) with the exception of the percentages of dome open clear and usable nights, which are taken from the ESPAS (ESO Search for Potential Astronomical Sites) Site Summary Series report on Mauna Kea5. The Campanas Peak numbers
5 Satellite estimates of the percentage of clear time at Mauna Kea range from 69% (Erasmus 2003) to 76% (Schöck et al. 2009). However, statistics of dome open clear nights indicate lower numbers ranging
29 Annex 1 to Cou-1296 conf.: SSAC Status Report E-ELT Site Selection Advisory Committee – Status Report, March 2010 – CONFIDENTIAL
are preliminary values from the GMT site testing program kindly provided by Joanna Thomas- Osip except that the dome open clear and usable percentages and the dew point usable time are those for Vizcachas which lies only 26 km to the south.
For reference, Table 4 also summarizes the properties of ESO’s present observatory at Paranal.
Table 4- Key site testing parameters; presented are night-time median values and where relevant and available the (approximate) range of values based on monthly average figures are indicated.
Parameter Mauna Kea Campanas Paranal Peak A- Dome open clear nights 45 % 66 % 75 % B- Dome open usable time 67 % 84 % 91 % 13 13 C- Temperature [C] 2.3 11.3 6 12.1 10 -1 9 7 D- Wind speed [m s ] 5.7 6.3 4 5.7 4 E- Wind speed usable time N/A 98 % 99 % F- Humidity 30 % 36 % 22 % G- Dew point usable time N/A 98 % 100 % H- Dust usable time N/A 100 % 100% I- PWV [mm] 1.9 3.1 2.34 J- Good mid-IR time 54 % 25 % 38 % 1.13 0.72 1.1 a K- DIMM seeing [″] 0.75 0.60 0.63 0.55 0.93 0.8 ) 0.48 0.50 0.57 L- MASS seeing [″] 0.33 0.27 0.45 0.38 0.47 0.36 4.2 8 M- Coherence time [ms] 7.83 3.45 2.0 3.64 2 3.2 2.2 2.7 N- Isoplanatic angle [″] 2.69 2.1 1.96 1.8 2.09 1.7
a) The relatively high median seeing for Paranal is due to a thin, turbulent surface layer, normally not affecting the VLT. See Section 3.4.
9. RECOMMENDATIONS
The wider search for suitable sites for the E-ELT gradually narrowed down to a handful of locations that have been intensely studied and the results of which are summarized in this report. The task of finding the best possible location for the telescope encompasses the assessment of a broad range of atmospheric parameters as well as aspects related to the cost and efficiency of its construction and operation. The E-ELT, because of its size, uniqueness, cost, and operational complexity poses even more stringent constraints on its location than the current generation of telescopes. For example, the stability of observing conditions is very important since opening and closing the dome will require more time than what is customary at smaller telescopes, while stable conditions will also provide a better chance of successful completion of an observing programme, an important factor considering the significant operating cost per unit of time. Furthermore, as the primary mirror will be unprotected and only be cleaned through a cyclic process of re-aluminizing mirror segments, protecting the optics from dust is from 41% (McNight & Jefferies 1968) to 56% (Morrison et al. 1973). As the TMT site testing group has not yet published an analysis of the expected dome open statistics for Mauna Kea, the SSAC has relied on the ESPAS report which, in turn, is based on the data of Kaufman & Vicchione (1981) covering the years of 1970-1978.
30 Annex 1 to Cou-1296 conf.: SSAC Status Report E-ELT Site Selection Advisory Committee – Status Report, March 2010 – CONFIDENTIAL
very important, as it may take a long time to recover fully from having a dirty mirror. And last but not least, since the telescope will exploit some kind of adaptive optics system most of the time, the characteristics of atmospheric turbulence are even more important than on the current generation of telescopes.
Having stressed what makes site selection for the E-ELT different or more critical from that of the current generation of ground-based optical/IR telescopes, it must be said that a fundamental requirement for the site of the E-ELT is the same as that for any other telescope: namely that the sky be as transparent and as dark as possible at wavelengths from the near UV to the mid- IR. Not surprisingly, the wide range of parameters considered requires careful balancing of pros and cons.
The five mountain tops that are considered in detail here are Armazones, Tolonchar, Ventarrones, Vizcachas and La Palma. We first consider Vizcachas and La Palma.
VIZCACHAS AND LA PALMA
For any ground-based optical-infrared telescope, having generally good sky conditions, i.e. a high incidence of clear and dark skies and good seeing are of fundamental importance. Overall, Vizcachas and La Palma do not score as good on these parameters as the best sites on the list; both suffer from relatively poor weather with 67% and 57% of clear nights, and 84% and 72% of usable nights, respectively. These percentages take into account the stringent operating parameters of the E-ELT as far as wind and humidity are concerned. La Palma does rank high in terms of free-atmosphere seeing and the site enjoys long coherence times for atmospheric turbulence, aspects that are attractive for adaptive optics operation (with the caveat that the dataset is biased towards the summer months). Both these sites have mediocre conditions for mid-IR observations as judged from their relatively high levels of precipitable water vapour. La Palma is known to suffer from regular dust storms, the main effects of which are incorporated in the above-mentioned percentages of clear nights (but not in the usable nights). However, elevated levels of dust in suspension, in presence of the Moon will increase the sky background, even in the regime where the telescope can remain operational. Furthermore, in particular for La Palma, the risk of increased light pollution is present even though the sky quality is protected by law, in particular if the island were to develop further as a touristic destination. For the design of the dome on La Palma the possible load of snow and ice has to be taken into account, for which engineering solutions can be found. Finally, for both sites, given their location the operational synergy with the facilities on Paranal is difficult to envisage, and in the case of La Palma, given its Northern location, the scientific synergy is limited with other key facilities such as VLT(I), VISTA, VSA, ALMA, SKA and the LSST.
Clearly both La Palma and Vizcachas are very good sites for astronomical observations, as is proven from the scientific successes that have come from the Roque de los Muchachos and La Silla Observatories. But as a location for the E-ELT the committee considers that both these sites fall short of fulfilling the very high expectations for the future scientific exploitation of the E- ELT and therefore the committee does not recommend building the E-ELT on either of these sites.
ARMAZONES
This location has captured the committee’s attention as being the best possible site for the E- ELT. Armazones enjoys excellent observing conditions overall, with a high fraction of photometric nights and only 11% of the time expected to be unusable due to weather conditions. The median seeing is excellent, while the free atmosphere seeing, turbulence coherence timescales and size of the isoplanatic angle should provide an excellent basis for adaptive optics exploitation. The low precipitable water vapour content shows that even though the mountain is only of moderate height, it is an attractive site for mid-IR observations. Skies are dark and are expected to remain so for the decades to come.
Armazones, being so close to the Andean subduction zone does carry the risk of being subjected to a major seismic event during its lifetime. This risk seems to be adequately taken into account in the engineering design work and can be reduced to an acceptable level, as has
31 Annex 1 to Cou-1296 conf.: SSAC Status Report E-ELT Site Selection Advisory Committee – Status Report, March 2010 – CONFIDENTIAL
been the case for the VLT. The impact of micro seismicity causes concern for the normal operation of the telescope, but this is treated as an additional source of vibration being injected into the system (like wind shake, pumps etc) that the active control loops of the telescope are anticipated to correct for.
With respect to the scientific opportunities that will be opened up by the E-ELT, the Armazones site offers excellent possibilities of taking advantage of cross-facility science programmes with the VLT, VLTI and other telescopes at Paranal, as well as with future new facilities such as ALMA, SKA, and the LSST. The committee stresses an additional advantage of this site: thanks to its relatively short distance to Paranal there are real possibilities of combining operational activities and sharing facilities that will work to the benefit of both locations. Such coordinated approach is expected to save significantly on the operations cost and will allow the use of specialist knowledge and skills in a coordinated fashion between the two mountain tops.
In summary, the SSAC strongly favours Armazones as the prime site for the construction of the E-ELT.
VENTARRONES
This mountain, not far north from Armazones enjoys excellent weather statistics with a very high fraction of clear time. Although the weather is very good, seeing conditions, both integrated over the whole atmosphere as well as the free-atmosphere seeing are clearly not as good as what has been measured on Armazones. Risk of seismic impact is similar to what is previously mentioned for Armazones. The scientific synergy of this site is identical to that of Armazones, and also operational synergy with Paranal offers good possibilities, although the distance is somewhat larger. Ventarrones appears to suffer from a relatively turbulent ground layer. Its impact may possibly be mitigated by the ground-layer adaptive optics system that is expected to become a standard feature of the E-ELT, but clearly it would be better if this turbulent layer were weaker. Ventarrones (or a location in its vicinity) could be a good site for the E-ELT, but further measurements are required and it should be assessed in detail what the scientific impact of the atmospheric turbulence would be, taking into account the performance characteristics of the telescope and the adaptive optics instrumentation.
We mention a third mountain in the Paranal area, Vicuña MacKenna where some preliminary measurements were made. This location has several general properties in common with both Armazones and Ventarrones and could be a promising alternative for Ventarrones, in particular if the lowest layers of the atmosphere turn out to be less turbulent. However, given the scarcity of data no firm conclusions could be drawn at the time of writing this report.
TOLONCHAR
This site enjoys good weather statistics, although not as good as that of Armazones. Tolonchar really stands out for its excellent seeing and very low precipitable water vapour column density, giving this site an advantage for adaptive optics and in particular for exploiting mid-IR wavelengths. Scientific synergy with other facilities is obviously as good as for the other Chilean sites. The sum of these arguments makes the committee rank Tolonchar amongst the very best. On the down-side, construction and operation of the E-ELT on Tolonchar will be significantly more expensive than in the case of Armazones, mainly because of its high elevation and remote location. The distance to Paranal implies that there are few options for achieving real operational synergy with the VLT, if any. As for the other Chilean sites, seismic events pose some risk, as well as that of volcanic activity that could affect operation. Achieving access to this site could be problematic for administrative reasons, and much care will have to be taken in respecting local cultural and social sensitivities.
Overall, Tolonchar is an excellent location for the E-ELT, but due to its somewhat higher weather down time, higher construction and operations cost, and generally higher risk related to securing the site for a rapid development, the committee places Tolonchar second to Armazones in our ranking.
32 Annex 1 to Cou-1296 conf.: SSAC Status Report E-ELT Site Selection Advisory Committee – Status Report, March 2010 – CONFIDENTIAL
We complete our recommendations with a general comment with respect to site testing. Until the future location for the E-ELT site has been firmly secured site testing should continue on the most promising sites in order to improve the statistical database. Moreover, after the site has been selected, the tests should concentrate and intensify there in order to establish the longest possible time base, and to monitor any changes that may occur due to the construction activity. In particular attention should be paid to the surface turbulence layer using SODAR, SLODAR and LuSci measurements. We also recommend that an environmental impact study be performed that would thoroughly evaluate all aspects, including environmental, cultural, socio- economic, and financial aspects of constructing and operating the E-ELT once the site is selected.
10. ACKNOWLEDGEMENTS
The conclusions in this report have only been made possible thanks to the efforts of a large group of people to plan, to construct and test instrumentation, to carry out the observations under often very difficult conditions, and to analyse the data and present the result to the committee. The efforts not only involved ESO’s E-ELT team but also groups working as part of the EU-funded 6th Framework Programme on astronomical site characterization, coordinated by J. Vernin from Nice University in France, staff from the Instituto de Astrofísica de Canarias in Spain, from the Instituto de Astronomía Teórica y Experimental from the Universidad Nacional de Córdoba in Argentina, and from the Cadi Ayyad University of Marrakesh in Morocco. Special thanks are due to the Thirty Meter Telescope project team who made available a tremendous amount of site testing data that provided valuable input to this work. Finally, the SSAC thanks ESO for their continuous support in assisting us in our task, and extend special thanks to Jorge Melnick and Marc Sarazin for their unlimited efforts in assembling, analyzing and reporting the site data in a way that tremendously simplified our task.
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Gonzalez E., 2009, Instituto de Astronomía Teórica y Experimental, Universidad Nacional de Córdoba. Internal report. Graham E., 2002: http://www.vt-2004.org/gen-fac/pubs/astclim/espas/espas_lib.htm Grenon M., 1990, The Messenger, 61, 11 Guerrero M. A., García-López R. J., Corradi R.L.M., Jiménez A., Fuensalida J.J., Rodríguez-Espinosa J.M., Alonso A., Centurión M., Prada, F., 1998, New Astron Rev 42, 529 Herrero Davó A., Arribas Mocoroa S., Barcons Jauregui X., Martinez Roger C., Cepa Nogué J., Gallart Gallart C., Rebolo López R., 2009, report on the workshop Science with the E-ELT in the Northern Hemisphere Hickson P, Lanzetta K., 2004, PASP 116, 1143 Hook I., 2005, The science case for the European Extremely Large Telescope : the next step in mankind's quest for the Universe, Edited by I. Hook. ESO publication. Hsu N.C. et al. (8 authors), 1999, Journal of Geophys. Res., 104, 6269 IPCC, 2007: http://ipcc-wg1.ucar.edu/wg1/Report/AR4WG1_Print_SPM.pdf Kaufman J. M. and Vecchione M., 1981, A Summary of nine years of weather data from Mauna Kea Observatory, UC TMT Report No: 66 Kerber et al, 2010, ESO internal report Kidder et al., 2000, in National Weather Digest 24, 25 Kissler-Patig M., Küpcü Yoldas A., Liske J., 2009, The Messenger 138, 11 Kornilov V., Tokovinin A., Voziakova O., Zaitsev A., Shatsky N., Potanin S., Sarazin M., 2003, Proc SPIE 4893, 837 Krisciunas K., Schaefer B.E., 1991, PASP, 103, 1033 Lombardi G., Zitelli V., Ortolani S., Pedani M., 2006, PASP, 118, 1198 Lombardi G., Zitelli V., Ortolani S., Pedani M., 2007, PASP, 119, 292 Lombardi G., Zitelli V., Ortolani S., Pedani M., Ghedina A., 2008, A&A, 483, 651 Lombardi G., Zitelli V., Ortolani S., 2009, MNRAS 399, 783 Lord, 1992, NASA Technical Memo 103957 Martin F., Tokovinin A., Ziad A., Conan R., Borgnino J., Avila R., Agabi A., Sarazin M., 1998, A&A 336, L49 McKnight, D.R., Jefferies, J.T., 1968, A Site Survey of Mauna Kea I. Meteorology, internal report Melnick J., Monnet G., 2010, ESO internal draft report on the Merit Function Melnick J., Sarazin M., Navarrete J., Lombardi G-L., 2010, ESO internal report on site testing data Michaille L., Clifford J.B., Dainty J.C., Gregory T., Quartel J.C., Reavell F.C., Wilson R.W., Wooder N.J., 2001, MNRAS 328, 993 Morrison, D., et al. 1973 PASP 85, 255 Moulin C., Chiapello I., 2004, Geophys. Res. Letters, 31, L02107 Moussaoui N., Holzlöhner R., Hackenberg W., Bonaccini Calia D., 2009, A&A 501, 793 Murdin P., 1986, RGO/La Palma Technical note n. 41 d’Orgeville C., Rigaut F., Boccasa M., Dainty C., Figueroa E., Flicker R., Gregory B., Michaille L., Quartel J., Tokovinin A., Trancho G., Wooder N., 2003, SPIE 4839, 492 Pedani M., 2004, New Astronomy, 9, 641 Roberts L.C., Bradford L.W., Neyman C.R., Liu A.Z., 2007, PASP 119, 787 Sarazin M., 1990, Final report of the VLT Site Selection Working Group; VLT report No. 62 Sarazin M., 1997, The Messenger, 90, 5 Sarazin M., Hinojasa R.H., Lombardi G., Navarrete J., 2009, ESO internal report Sarazin M., Lombardi G., Navarrete J., 2008, ESO internal report Sarazin M., Melnick J., Navarrete J., Lombardo G., 2008, The Messenger, 132, 11 Sarazin M., Roddier F., 1990 A&A 227, 294 Saussen et al., 1998, Theoretical & Applied Climatology 61, 127 Schöck, M., 2004, SPIE 5489, 95 Schöck M., Els S., Riddle R., Skidmore W., Travouillon T., Blum, R., Bustos, E., Chanan, G., et al., 2009, PASP, 121, 384 Skidmore W., Els S., Travouillon T., Riddle R., Schöck M., Bustos E., Seguel J., Walker D., 2009, PASP 121, 1151 Tamai R., 2009, ESO internal report Tokovinin A, 2002a, PASP 114, 1156 Tokovinin A, 2002b, Appl. Optics 41, 957
34 Annex 1 to Cou-1296 conf.: SSAC Status Report E-ELT Site Selection Advisory Committee – Status Report, March 2010 – CONFIDENTIAL
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The Committee, stranded in the Atacama Desert (photo courtesy M. Kissler-Patig)
35 European Organisation for Astronomical Research in the Southern Hemisphere Annex 2 to ESO/ Cou-1296 conf.
Annex 2. Offer by the Chilean government
Annex 2 to Cou-1296 conf. Chile Offer, Original Spanish Version
1 Annex 2 to Cou-1296 conf. Chile Offer, Original Spanish Version
2 Annex 2 to Cou-1296 conf. Chile Offer, Original Spanish Version
3 Annex 2 to Cou-1296 conf. Chile Offer, Original Spanish Version
4 Annex 2 to Cou-1296 conf. Chile Offer, Free English Translation
THE MINISTER OF FOREIGN AFFAIRS OF CHILE
12th. February, 2010
Prof. Dr. Tim de Zeeuw Director General European Organization for Astronomical Research In the Southern Hemisphere ESO
Dear Dr. Tim de Zeeuw,
Through special instructions from the President of the Republic of Chile, I am pleased to address myself to you and, through you, to the members of the Council of the European Organization for Astronomical Research in the Southern Hemisphere (ESO), with the aim of conveying our country’s highest interest in realising the possibility of installing the European Extremely Large Telescope (E‐ELT) in our territory.
As you know, the long and fruitful relationship between the Government of Chile and ESO is governed by international treaties, ratified by our National Congress, which have satisfactorily regulated our relations for over 40 years and have laid the foundations, in a solid and stable manner, for fruitful cooperation bonds.
Moreover, the agreements in force grant the members of ESO the diplomatic prerogatives, facilities and exemptions appropriate to an international organization, which enormously facilitates and simplifies its operations in our country.
Within this framework, I would like to convey, on behalf of our Government, the following proposal:
1. Land for the installation of the E‐ELT. a. The Government will contribute, within the frame of the existing legal procedures, to the installation of the Telescope E‐ELT by transferring ownership, free of charge, of an area of 18.900 hectares, located around Armazones, whose coordinates were specified in your letter dated 19 January, 2010. The concession can be granted as from 2011, once the existing concession granted to Universidad Católica del Norte (UCN) over this same area expires.
1 Annex 2 to Cou-1296 conf. Chile Offer, Free English Translation
b. Likewise, the Government will grant a concession free of charge of an area of 36.200 hectares, with the aim of protecting the operation of the E‐ELT, corresponding to land adjoining the area mentioned in the previous paragraph and whose coordinates were also stipulated in the letter referred to above.
c. It should be noted that the total area of land specified above is part of an “astronomical protection preserve”, defined by the National Commission for Science and Technology of Chile, with all the benefits of scientific exclusivity that this implies.
d. The above proposal is subject to the mutual understanding that ESO will reach an agreement with Universidad Católica del Norte (UCN) and the University of Bochum in Germany, to ensure that the astronomical research facilities belonging to these institutions, installed in the mentioned areas, will not only be duly safeguarded, but that they will also benefit from the installation of the new Telescope.
2. Observing Time a. The Chilean astronomical community fully supports the installation of the E‐ELT, and considers it as an extension and strengthening of the current scientific cooperation between Chilean astronomers and those from the ESO Member States. In order to reinforce this goal, the same conditions about the observing time agreed for the Telescopes VLT and VLTI at the Paranal Observatory and defined in the Agreement in force, shall apply to the E‐ELT. These conditions have facilitated the close collaboration mentioned above.
b. The Joint ESO‐Chile Committee, within the frame of the attributions defined in the aforementioned treaties, will follow up the implementation of the observing time conditions mentioned in the previous paragraph, identifying modifications they may deem necessary in the future, with the aim to promote, extend and make more effective the cooperation in astronomical research between Chile and the ESO Member States.
3. Infrastructure support a. Power supply In Chile, the Government does not develop nor operate electrical infrastructure to supply energy to third parties, conferring this function on private enterprises, which are involved in the production and distribution of electric power. The Chilean Government, through a working team supervised by the Ministry of Energy, will elaborate and coordinate the actions necessary to manage with the companies of the electrical sector the best options, both to develop the required transmission infrastructure, as well as to contract electrical power supply for ESO’s Paranal Observatory, including its extension to the E‐ELT to be installed at Cerro Armazones. These options shall be defined in advance of the initiation of the telescope’s construction.
2 Annex 2 to Cou-1296 conf. Chile Offer, Free English Translation
b. Access and communications. The Government of Chile, through the Ministry of Public Works has invested, during the last years, over US$ 20 million to improve the 120Km road from Antofagasta to the current access to Paranal, particularly the semi‐coastal road, thus ensuring a high standard connection. In the future, the Government will have at its disposal the means to make the necessary investments to permanently ensure the optimum maintenance of this road.
c. Connectivity and other services. The Government, through the relevant institutions, will grant all facilities within the legal framework to ensure fiber optic or other interconnections required for the joint operation of the Paranal‐Armazones complex.
4. Scientific and technological cooperation in the construction and operation of the E‐ELT. a. Chile has decided to establish an Innovation Fund for the development of astronomy and associated technologies, which will be jointly operated through the National Commission for Scientific and Technological Investigation (CONICYT) and the Corporation for the Promotion of Production (CORFO) through the Committee of Innovation (Innova Chile‐CORFO). This competitive Fund will be available for research centers of Chilean universities and related enterprises in this sector, which will be able to submit proposals jointly and with contributions from foreign institutions for the development of projects of interest for astronomy in Chile. These projects will be able to refer as much to the development of instrumentation, services and operating systems of the telescopes, as well as creation of public‐private consortia to participate in these projects.
b. With the support of this Fund, Chile proposes to agree with ESO on a mechanism of scientific collaboration, funded by both parties, to develop services and technologies associated with the development of the E‐ELT, which also includes training for scientists, engineers and technical specialists which facilitate and make more efficient the development and operation of the E‐ELT in Chile and the astronomical installations in the national territory in general.
c. With the objective of facilitating the construction and operation of the E‐ELT, our Government requires that it is guaranteed that Chilean construction and engineering companies, by themselves or in association with foreign enterprises, in particular from ESO Member States, will receive all necessary information to participate actively in the calls for tender related to this project.
3 Annex 2 to Cou-1296 conf. Chile Offer, Free English Translation
As you know, the relationship between our country’s Government and ESO is a strategic relationship, based on a long‐running cooperation, confirmed by successive investment projects in new instruments and crowned by scientific research results that have made important contributions to world astronomy.
Our country not only offers conditions of exceptional quality for astronomical observation through clear, stable and transparent skies but also, currently, as a result of our collaboration, the country can offer a community of astronomers, engineers and technicians who can ensure an optimum development for current and future operations of ESO in Chile.
With best regards,
MARIANO FERNANDEZ AMUNATEGUI
4 European Organisation for Astronomical Research in the Southern Hemisphere Annex 3 to ESO/ Cou-1296 conf.
Annex 3. Offer by the Spanish government
Annex 3 to Cou-1296 conf. Spanish Offer
1 Annex 3 to Cou-1296 conf. Spanish Offer
2 Annex 3 to Cou-1296 conf. Spanish Offer, Supporting Document
La Palma as the European Site for the E-ELT
30 November 2009 Annex 3 to Cou-1296 conf. Spanish Offer, Supporting Document
La Palma as the European Site for the E-ELT
Summary La Palma has demonstrated to be a high-quality Besides that, La Palma presents the lowest observing site for professional astronomy over seismic risks. According to the studies carried the last three decades. More than 60 research out about the seismic and volcanic hazards in institutions, from 19 countries, have installed several observatories (Chile, Hawaii and the their telescopes at the summits of Tenerife and Canary Islands), the lowest geological hazard La Palma under bilateral agreements with in both seismic and volcanic activities occurs Spain as hosting country. The Teide and Roque by a large margin in La Palma. These benign de los Muchachos Observatories (OT and ORM geological conditions are expected to have a respectively) are nowadays a mature and favourable impact on the telescope construction favourable neighbourhood for the E-ELT, and maintenance costs. allowing the highest autonomy for this inter- The geographical and socio-political situation national project under ESO’s Programme, but of La Palma provides also several advantages offering also top-grade conditions for optimal of interest for the E-ELT. operation of this new facility. First, La Palma is part of the European The main site offered by Spain to ESO for the Union, which brings several benefits such as installation of the E-ELT is located at the having the same currency (euro) and facili- Roque de los Muchachos Observatory (ORM), tating the exchange of goods and people. Spain, on the edge of the Caldera de Taburiente as EU Member State, offers a stable financial National Park, 2.396 m. above sea level on La environment and experiences inflation indices Palma (The Canary Island, Spain). ESO would similar to other ESO member states. be awarded full privileges, immunities and complete autonomy at the site provided for the Furthermore, the Canary Islands (therefore, installation of the E-ELT and for other ESO La Palma) is one of the Outermost Regions premises, but could benefit also from the of the European Union, which offers the presence of an established Observatory with an opportunity to access EU funds devoted to the important infrastructure and human resources. development of these areas and brings special The current situation is that the Observatories measures and tax advantages awarded to these at the Canary Islands are very well equipped regions. In particular, the IGIC (5%) is applied and adapted to host the new generation of large instead of the VAT. Additionally, special and extremely large telescopes, such as the E- regulations exist at the Canary Islands to ELT. Physical and logistic requirements for the encourage astronomical research, in the form E-ELT in La Palma are attainable in a short that astronomical instruments imported into La time scale. Palma do not pay taxes. These exemptions are in addition to those covered by the Protocol on The astronomical quality of the La Palma Privileges and Immunities. summits is protected by Law and its atmos- pheric parameters have been continuously Second, La Palma is closest to mainland monitored for decades. Since this topic is Europe (and, particularly, to ESO HQ in under evaluation by the Site Selection Advisory Germany) than other potential sites. A shorter Committee (SSAC), this document will not go distance brings advantages from different into further details about sky quality. points of view: trips are more ergonomic and affordable; the delivery of goods is easier, From the scientific point of view, even if there consumes less time and is more economic; are unique astronomical targets in both international staff could be easily relocated to hemispheres, supporting facilities, synergies the island, and, finally, this convenient distance and preparatory surveys can also be found in to Europe can help to stabilize the personnel both, and first-rank Science (the ultimate and, therefore, to maintain expertise. goal of the E-ELT) can be carried out independently of the Hemisphere. These facts ensure financial stability to meet the scheduled construction and operation costs It should be noted that La Palma can observe for the E-ELT. From the point of view of 1/2 of the Southern Hemisphere, and that it recruiting and stabilizing the staff, it is also shares 1/3 of the sky with other ESO facilities worth mentioning, first, that the scientific (VLTI and ALMA) in favourable observing institutions already present at ORM and OT conditions. Therefore synergies across the hold a superb pool of highly-qualified whole ESO programme could be exploited in a international staff; and second, that La Palma large fraction of the sky.
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La Palma as the European Site for the E-ELT offers a very nice place to live thereby Privileges, immunities and autonomy retaining this staff. The island enjoys pleasant following ESO standards will be endorsed, temperatures in all seasons,; provides a very as already done with other European attractive natural environment, with the institutions, like the ESA European Space possibility to enjoy a lot of different open-air Astronomy Centre close to Madrid. Extra activities; and possesses the infrastructure privileges and exemptions, thanks to the (schools, hospital, medical centres, etc.) that experience obtained after 30 years prioritizing people and their families need. astronomy at the Canary Islands, will be possible. Moreover, the legal context that Additionally, the shorter distance between La exists in Spain, as an EU Member State, means Palma and ESO Headquarters (Garching) has that local staff or families of ESO staff, not the additional benefit of only one-hour local having diplomatic status, will automatically time difference between both locations. This enjoy European community regulations. small difference makes the working hours in both places almost the same, which facilitates It is also worthy to mention here that main the communication between the teams located public authorities and other stakeholders in in ESO HQ and the E-ELT. La Palma and in Spain have shown their interest and formal support to the ins- La Palma summits are a one-hour drive tallation of the E-ELT in this Island. This is from Santa Cruz de La Palma (the capital of of extreme relevance since it allows all permits the Island, which is located at sea level). This for the construction of the E-ELT and other unusually short distance makes personnel ESO’s premises to be granted in a very short displacements to the E-ELT easy and time scale. This period has been around 6 ergonomic. In particular, the ORM short months in total for the last facilities erected at distance to the sea level can be a key parameter ORM. to optimize the E-ELT Operation Site Plan, in the sense that not all the operation and Finally, it is very usual that the country hosting maintenance activities must be performed on a telescope or a complete observatory receives the mountain. Trade-off logistic analysis could a fraction of the useful time available. This be considered to decide which ones should be observing time oscillates between 10% and carried out in a Sea Level Facility instead of 20% (as in the case of ORM). the E-ELT site. In case the E-ELT is located in La Palma, In this sense, experience accumulated by other there would be no reserved time for Spanish telescope facilities in La Palma, which combine astronomers, which implies that 100% of the operational activities at the summit and sea observing time will be available to be level, could illustrate the potential benefits of distributed among the ESO Astrophysical this trade off. Community. Besides simplifying science operations, this will result in a higher scientific The ORM provides an already established return to ESO member states. infrastructure and several improvements are underway. Apart from those facilities to be owned and directly operated by ESO, the E- ELT could take advantage of some of these current infrastructures, which would allow a major reduction of the Operations budget and simplify the Site Operations Plan. In particular, the following key infrastructures would be available to ESO, by means of direct contracts with the supplier companies or through the Observatory: electrical power supply, canalized water supply and water drainage, high bandwidth data communication lines, garbage disposal, maintenance of the main roads, security, first aid and fire protection systems. Spain has also demonstrated in the past a responsible and very positive attitude to offer the most advantageous conditions to host international organisations, their projects and staff.
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INDEX
FOREWORD .…….……….…………………………………………………. 2
SUMMARY ………..……………………………………………………………. 3
LA PALMA SITE ……………………………………………………………… 6 General overview ………………………………………………………………… 6 Protection of the sky …………………………………………………………….. 7 Geological aspects …..….…………………………………………….…………. 8 Synergies with ORM User Institutions. A favourable environment .……….…… 10 Site description, services and facilities ………………………………………….. 12 Potential sites for the E-ELT and other ESO premises at La Palma .….………... 15 Logistical aspects and social environment ……………………………………… 16
LEGAL ISSUES …………………………………………………………………. 18 Privileges and Immunities ………………………………………………………… 19 Applicable Law and autonomy ….……………………………………...... ………. 19 Availability of land and ownership …….…………………………………...…….. 20 Taxes .…………………………………………………………..……………….… 21 Construction support and building permits ……………………………………….. 22
Appendix 1: Science with the E-ELT in the Northern Hemisphere ……..…. 23
Appendix 2: List of public authorities in Spain and other stakeholders ……. 26 supporting the construction of the E-ELT in La Palma
5 / 26 INDEX Annex 3 to Cou-1296 conf. Spanish Offer, Supporting Document
La Palma as the European Site for the E-ELT
LA PALMA SITE General overview La Palma is part of the Canary Islands archipelago (a Spanish autonomous commu- nity). The archipelago consists of seven major islands, one minor island, and several small islets. They are of volcanic origin and can be found in the North Atlantic Ocean, just off the coast of the north-western portion of the African continent (108 km). They comprise north-easterly pattern of winds at sea level, two provinces, Santa Cruz de Tenerife and Las which are cool and humid from passing over Palmas. La Palma belongs to the province the maritime current of the Canaries, whilst the Santa Cruz de Tenerife. winds at mid-level are north-westerly, dry and warm. As a result of these factors, at the It is also one of the world’s most mountainous latitude of the Canaries’ archipelago the islands. Its highest peak, where the Observato- frequent presence of a near subtropical rio Roque de los Muchachos (ORM) is anticyclone, the predominance of the Trade located, reaches up to 2,426 metres. Winds and the existence of a cold ocean As the other Canary Islands, La Palma is current, there is a stratified air with largely volcanic in origin. It has many cones; lava stable layers. flows and dykes which make a sharp contrast The climate’s main feature is the persistence to its stunning floral wealth. of a vertically structured troposphere with frequent inversions, which causes much more horizontal (rather than vertical) air circulation. This usually prevents air from rising and producing the convective phenomena that would cause precipitation. There is normally an inversion layer between 1.200 and 1.600 m, thereby producing a clear dividing line between the lower and upper layers of air circulation and defining a completely different climate to those featuring areas below the inversion layer. Therefore, meteorological conditions in the lower and upper parts are La Palma offers in a small area a variety of quite different. Meteorological conditions at landscapes: mountains, volcanoes, forests, ORM: beaches, a temporate rainforest, tiny villages and breathtaking views. For this reason, the Average Temperature: 9.9±6.1ºC (day) / main attractions of La Palma are open air 7.6±5.5ºC (night) activities such as diving, windsurf and Minimum and maximum recorded trekking. temperatures (2000-2003) are: -9.60ºC and 28.10ºC respectively. The island is also a privileged place for astrophysics. Its particular geographical posi- Average wind speed: 4.8±3.0m/s (day) tion and climate causes clouds to form and 5.2±1.6m/s (night) between 1.000 m and 2.000 m, usually leaving Dominant wind direction (GTC location, the summits of the island (2.400 m above sea night-time) is North-East, due to local level) with a clear and dry sky. orographical influences. The climate of these Islands is dominated by a The Biosphere Reserve of La Palma was persistent area of high pressure in the North declared in 1983, extended and renamed in Atlantic (known as either the Azores 1997 and 2002. The biosphere reserve now anticyclone or the Bermuda High), which is encompasses the entire island, which contains normally situated over the North West of the a wide range of representative habitats with all archipelago. Air circulation caused by the the diversity provided by the transition from anticyclone gives rise to a predominantly the coast up to the mountain peaks.
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Protection of the sky The astronomical quality of the sky at the Canary Islands’ Observatories is protected by Law.
On the 31st October 1988 the Spanish limit their radiation power in the direction of Government passed the Law for the Protection the observatories to a minimum. of the Astronomical Quality of the Canary Atmospheric pollution controls activities that Islands’ Observatories (Law 31/1988), which could damage the atmosphere over the was proposed by the parliament of the Canary observatories to prevent atmospheric pollution. Islands. On March 1992 the government The gases released into the atmosphere approved the Regulations for the law (R.D. resulting from human activity have adverse 243/1992). This law makes the Canary effects on weather and affect the health of Islands’ Observatories a legally protected site humans, animals and plants. A deterioration of (in effect an astronomical "reserve"), where air quality also leads to deterioration in continued dark skies, low radio frequency astronomical observations. fields, and control over other sky-polluting effects (including aircraft flight paths) are The law places limits on the amount of guaranteed. The law deals with 4 main areas: industry and polluting activities permitted at altitudes of more than 1,500m above sea level. Light pollution regulates exterior lighting on Although there have not been any attempts to the island of La Palma and the area of Tenerife build industrial facilities above this altitude, directly visible from it to prevent light the Law would prevent such activities. pollution. This is a generic term for all of the undesirable effects of artificial light. One of Aviation routes regulate air traffic over the the most damaging effects for astronomy is observatories to prevent interference from brightness or glare in the night sky caused by aviation routes. Aviation routes cause artificial light reflecting off gases and particles pollution in the form of clouds of condensed in the air. Unsuitable light fixtures shining exhaust gas and other combustion gases, upwards or outside the area they are intended which can affect the clarity of the sky. One of to illuminate and excessive lighting are the greatest successes to protect the responsible for these damaging effects. Any observatories was the designation of the lighting scheme within the area regulated by airspace above them as an "Ecological the Sky Law must comply with certain strict Protection Zone” on 17th May 1998. Air regulations. routes and flights of aircraft should be kept away more than 10 degrees above the horizon Radioelectrical pollution sets limits for as seen from the observatory and also keep electromagnetic radiation so that it does not more than 5 kilometers of horizontal distance. interfere with equipment or corrupt results at the observatories and prevents radioelectric The Sky protection law is applied in the pollution. The Law sets electromagnetic whole island of La Palma. radiation limits to ensure that equipment and The IAC (Instituto de Astrofísica de Canarias) measurements at the observatories are not runs the Sky Quality Protection Technical corrupted. Office (OTPC), with the goal of facilitating the The installation and operation of radio- implementation of this Law. communications stations are regulated with a power flux density limit of 10-6 W/m2 in force over the observatories. Power flux density for any frequency must not be greater than 2x10-6 W/m2 in any part of the observatories, equivalent to an electric field intensity of 88.8 dB (mV/m). The cumulative effect of the interferences caused by multiple radio stations (using the quadratic sum defined by the International Radio Consultative Committee) must be taken into account. Radio stations take measures to
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Geological aspects La Palma summits offer the lowest geological hazard, in both seismic and volcanic activity, among the top-class professional observatories in Chile, Hawaii and the Canary Islands. Some of the best astrophysical observatories in The VLT/I has survived intense earthquakes. the world, namely the Canarian, Chilean and In 2006, October 15th, the west coast of Hawaiian observatories are located within Hawaii experienced a 6.7 mb earthquake active geological regions. This is not a followed by a 6.0 mb aftershock and many coincidence, since topography modelled by smaller aftershocks. There was no significant tectonic and/or volcanic activity is a main structural damage at the telescope facilities; factor controlling the local atmospheric however the recovery to full science conditions and, hence, the sky transparency, operability at Subaru, Keck I and II and which usually defines good astronomical sites. Gemini North telescopes took several weeks. Increasingly larger telescopes (10 and 40 Based on the results from a comparative metres classes) demand stable structures and analysis of the hazard associated to seismic buildings, and hence geological activity and volcanic activity at several world-class becomes an important parameter to take into observatories1 (ORM, OT, Paranal, Mauna account when designing and constructing large Kea and Cerro Ventarrones), it can be telescopes. The structures of large telescopes concluded that the lowest geological hazard, in have and will have to withstand the effects both seismic and volcanic activity, happens at associated to seismic and/or volcanic activity, the ORM. On the contrary, seismic hazard is but they also have to minimize the loss of very high in Paranal and Ventarrones and in operational time, recalling the extreme Mauna Kea. This analysis has been carried out precision in the alignment of mechanical and by experienced researchers and published in optical components. This is well known to peer reviewed international journals. ESO, who built and continues operating the most successful optical/IR ground-based suite of telescopes in a geologically active area, Figure shows Earthquakes between 4 and 6 mb as registered by the National Earthquake Information thanks to the most careful and sophisticated Centre (NEIC) during the period 1973 – 2008. Red dots system. indicate the location of the observatories. Chile left, Hawaii up-right and Canary Islands bottom-right.
1 “Comparative analysis of the impact of geological activity on astronomical sites of the Canary Islands, Hawaii and Chile”. Eff-Darwich, A. et al. 2009, sent to MNRAS (astro-ph. April 2009, *arXiv:0904.0140) 8 / 26 La Palma Site Annex 3 to Cou-1296 conf. Spanish Offer, Supporting Document
La Palma as the European Site for the E-ELT
This plot shows the spatial distribution of the Observatory Peak Ground Acceleration hazard as the 10% chance of exceedance of (PGA) some ground motion parameter for an g exposure time of 50 years. Black dots mark the Mauna Kea 0,5 location of the observatories. Table offers Paranal 0,47 seismic hazard expressed in terms of the Peak Ground Acceleration (PGA) with 10% chance Ventarrones 0,42 of exceedance for an exposure time of 50 ORM 0,05 years. Teide 0,06
Ground deformation: Present-day telescopes Hazard associated to lava flows during a reach precisions in pointing and tracking volcanic eruption is not significant at any site, below 1 arcsec, hence stability is required in as the result of low volcanic activity in the both the telescope structure and the ground. regions where the sites are emplaced, This is particularly important for long baseline topographical protection or distance to the interferometers, where precisions better than eruptive vents. 20 µm are required in the alignment of Hazard associated to volcanic ashfall is mechanical and optical components. A negligible at Mauna Kea and ORM and low to theoretical analysis was carried out to infer the moderate in OT and the observatories in Chile, ground deformation, in terms of ground tilt, depending on the prevailing winds and the still associated to a dislocation induced by a fault. poorly known explosive volcanic activity in It is observed that a significant ground tilt of at these regions. least 1 arcsec might affect the Chilean sites, whereas the effect of ground tilt is less likely Concerning local seismic noise or micro- in Hawaii and Tenerife and negligible in La seismicity, according also to the work carried Palma. Thanks again to the sophisticated out by same experts at OT and ORM, it can be correction system, the VLTI in Paranal can concluded that there is not any amplification operate under unfavourable geological risk of structural vibrations in large telescopes conditions and keep fringe tracking even (10 meters or more) that could be installed at during moderate intensity seismic motions. the Canary Islands in the future.
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Synergies with ORM User Institutions A superb scientific and technical environment and highly qualified staff.
La Palma has demonstrated to be a high- in other major observatories, operating also quality observing site for professional astro- under visitor mode. nomy over the last three decades. During this Teide and Roque de los Muchachos Obser- time, a continuous characterization and vatories (OT and ORM respectively) are monitoring of the most relevant parameters has currently a mature and favourable neighbour- been carried out to measure the transparency hood for the E-ELT, allowing absolute of the sky, the number of usable observing independence for this international project hours and atmospheric optical conditions. under ESO Programme, but providing also the These favourable conditions, and formal best surrounding conditions and synergies for protection by Law as previously mentioned, optimal operation of this new facility. have been crucial to make possible, nowadays, that more than 60 research institutions from 19 This international club around astronomy at countries have installed their telescopes at the the Canary Islands, with top-class facilities for summits of Tenerife and La Palma, under astrophysical research, has made it possible to bilateral agreements with Spain, . attract also to these islands all the supporting elements and infrastructures needed to connect Even the local phenomenon known as the this field of research worldwide. La Palma has calima (very fine clouds of dust in suspension been astronomically fertilized for thirty-years, from the African Desert), has not had a severe allowing an easier construction and operation impact on the astronomical quality and of the E-ELT. Highly qualified staff, facilities, achievements in attracting top-class facilities etc, are likely to be accessible close to the at the Canary Islands’ observatories. These ORM (and retainable!), thanks to the dust episodes occur very often in coincidence continued astronomical activities at this site. with high cirrus, which means that the time lost for this reason is mainly accounted for and The fleet of telescopes at ORM is quite already deducted from the actual number of extensive, covering not only night-time photometric nights. observations but also Solar Physics and High Energy Astrophysics. Some of the main In fact, and based on lengthy statistics from a scientific facilities are described below. number of telescopes operating in visitor mode at the ORM, the percentage of effectively used observing time for astrophysical research has been around 76% during the last years; a fraction of time very similar to that one found
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Gran Telescopio Canarias The Telescopio Nazionale Galileo (TNG), (GTC) is a 10,4 m segmented with a pri-mary mirror of 3.58 m, is the telescope, which started ope- national facility of the Italian rations in March 2009. Main astronomical community. Its science drivers for the GTC main feature is the presence of are image quality, operational an Active Optics system to efficiency and reliability. The perform real-time, low GTC Project is a Spanish frequency correction of the optical initiative, led by the IAC, with the components in order to ensure the best participation of Mexico (IA-UNAM and performances in all conditions and to INAOE) and the US University of Florida compensate for the deformations of the thin (UFL). The telescope was built and is now primary mirror. operated by GRANTECAN, a public enter- The Liverpool Telescope (LT) is a fully prise jointly owned by the Governments of robotic astro-nomical 2m Spain and the Canary Islands. telescope owned and operated The Isaac Newton Group of Telescopes (ING) by the Astro-physics Research operates the 4.2 metre William Herschel Institute of Liverpool John Telescope (WHT), the 2,5 m Moores University in England. Isaac Newton Telescope LT is fully autonomous. (INT) and the 1 m Jacobus The MAGIC Telescope Collaboration has Kapteyn Telescope (JKT) built two Cerenkov on behalf of the Science and telescopes to study high Technology Facilities Council (STFC, United energy gamma rays in the Kingdom), the Nederlandse Organisatie voor TeV range. The project is Wetenschappelijk Onderzoek (NWO), and the funded primarily by the IAC. Due to the diameter, high-class funding agencies BMFB (Germany), MPG instruments and very good location of this (Germany), INFN (Italy), and MICINN telescope, the 4.2 m WHT has been widely (Spain). considered as one of the best medium-sized telescopes in the world. The Mercator Telescope is a 1.2 m semi- robotic telescope. It is operated by the As already mentioned, although University of Leuven (Belgium) in the ORM has ideal conditions for collaboration with the Observatory of Geneva night observations, it is also used (Switzerland). The Mercator Telescope has a for Solar Physics. The 1m flexible operational scheme, which allows Swedish Solar Telescope (SST) optimizing detailed monitoring campaigns on has provided high-resolution images of very different timescales. remarkable quality. SuperWASP is an extremely wide field The Dutch Open Telescope robotic camera, capable of imaging the entire (DOT) is also an optical solar visible sky every 45 minutes or so, designed to telescope with a main mirror detect exo-planets via the transit technique of 45 cm that can reach an around relatively bright stars. The instrument 0.2 arcsec resolution for is managed by a Consortium of UK and sustained periods. For further optimization, the Spanish based astronomers (the WASP DOT uses the image de-speckle mechanism. It Consortium). Finally, the Meridian Telescope is an open telescope, and the wind can blow is dedicated to carrying out high-precision through. It belongs to the Utrecht University optical astrometry. (NL) and has been funded by the Dutch Technology Foundation. A pool of human and technical resources of high specialisation: All these User Insti- The Nordic Optical Telescope tutions constitute with the IAC the ORM (NOT) is funded and operated community. Together, including also premises by a consortium from Denmark, at sea level, they represent more than 170 Sweden, Iceland, Norway and persons on site (25% scientists, 60% Finland. It has a main mirror with a 2,56 m engineers/technicians, 12% administration and diameter and was the first major telescope 3% others), fully dedicated to the best facility designed to use active optics to correct operation of current scientific facilities at the shape of a thin, lightweight primary mirror ORM. supported on actuators on the site.
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Site description. Services and facilities The ORM is already equipped with well-established basic and advanced infrastructure for astronomical research at La Palma. Requirements for the E-ELT are attainable in a short time scale. longer stays. Meals are served in the canteen and reception is available 24 hours per day during the whole week. This residence is equipped with standard communication facilities, meeting room with video- conferencing system, computer room and Wifi, and relaxation facilities. The average use of the residence accommodation services is approximately 9,500 stays per year. After the GTC arrival to the ORM, the residence is reaching its capacity limit and a project to upgrade it is currently under discussion. There is also a potential site The main site offered by Spain to ESO for the available for a new 60-room residence, installation of the E-ELT is located at the canteen for 150 persons and parking area, Roque de los Muchachos Observatory (ORM), exclusively for the E-ELT if needed, within 3 on the edge of the Caldera de Taburiente kms from the location proposed for this National Park, 2,396 m. above sea level on La telescope. Palma (The Canary Islands, Spain). ESO could decide either, to build its own The ORM is located in the “buffer or damping residence and canteen within 2-3 km from the zone” as defined by the UNESCO Man and E-ELT location, or to agree with ORM the Biosphere Programme (MAB) for World extension and improvement of the current one Biosphere Reserves. to provide this service to both communities, ESO would be awarded full privileges, following ESO requirements and under immunities and complete autonomy at the site adequate priority conditions and privileges. provided for the installation of the E-ELT and Power supply: The power supply is provided for other ESO premises, but also could benefit by the regional company UNELCO. Currently, from the presence of an established a cable of 15 kv coming from Garafía observatory with an important infrastructure Municipality reaches the ORM. This line is and human resources. able to provide up to 3 Mw, although the The current situation is that the Observatories current consumption in the ORM is not more at the Canary Islands are very well equipped than 0,8 Mw. Each telescope facility must and adapted to host the new generation of have its own transformer station as well as, if large and extremely large telescopes, such as desired, its own back-up power break system the E-ELT. Physical and logistical require- (UPS and power generators). The consumed ments for the E-ELT in La Palma are power of each institution is registered in an attainable in a short time scale, since many of independent manner and is charged to this these requirements (power lines, commu- institution. The current price is around 0,08 nication lines, fuel, water, etc) are already €/KWh. supplied to the ORM User Institutions, or in A project to improve the electricity supply is process to be supplied or improved. Some of already under discussion with the Government these services and facilities are described of La Palma. Currently, the more likely option below. and recommended by UNELCO is to lay a Residence and Canteen: The ORM residence new line of 66 Kv from the town of Punta provides accommodation for astronomers and Llana. This will be an overhead line through other professionals working or visiting the the areas not protected until it reaches the observatory. It has 31 single rooms and 27 “Pico de las Nieves” and, then, be buried until double rooms, including an annex building for the ORM proximity. At the observatory, a
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La Palma as the European Site for the E-ELT central high to medium voltage transformer Gasoline supply: The Observatory has a will ensure the electrical supply to each private gasoline station, which can provide scientific facility. This new line will provide gasoline and diesel. This station was built to up to 10 Mw, as required by the E-ELT. A supply fuel for internal transports and, also, to back-up power generating this capability close help the scientific facility vehicles in case of to the E-ELT is also possible and foreseen. emergency. Special needs for the E-ELT could be satisfied. Water supply: Each telescope facility at the Observatory has its own water tanks and pays Communications: There is a switchboard in the water supply to an external service. In case the residence, which distributes the different of emergency, the common services can lines requested by the scientific facilities to provide water from their tanks to the scientific each institution. An internal LAN, which facilities. Currently, a project is in process to provides Ethernet data lines to each institution, be approved to canalize water supply, drainage also exists in the ORM. The data lines are part and fire hydrants to each telescope. This of the IACNET network system, which project, which has a budget of 4 M€, will start provides the data communications between all in 2010 and will last 18 months. The water the IAC sites (observatories, CALP and system includes 6 km of rising pipes, 7 km of headquarters in La Laguna). Recently, a new pipes for delivery and distribution and 8 km of project to upgrade this data line has been drainage pipes. This installation will use a completed, and it supports now up to 10 reservoir of 1.000 m3 in Hoya Grande. The Gbit/sec. Additionally, the connection from water will be elevated (1.200 m) in two ORM site to the national and international data tranches of 600 m each, using intermediate networks is being improved with a new dark tanks of 50 m3. The installation will be fibre network. This project (RedIRIS-Nova), underground with pipes designed to withstand which will be executed before the end of 2011, pressure, temperature and impacts. This has a budget of 130 M€. This new infras- system will feed the distribution warehouse of tructure could accommodate a high-speed data 350 m3 in the ORM. From this tank and using connection link between the E-ELT and ESO gravity, the water will be distributed to the headquarter. scientific facilities, residence and the future Garbage: Currently, twice per month, the visitor centre. If needed, a dedicated water common service truck picks up the garbage storage exclusively for the E-ELT, with from the scientific facilities containers, which similar capacity for fire fighting and drinkable is disposed of at an authorized dump in the water, could be considered. municipality of Garafía. This service can be A drainage system is also included in the adapted to accommodate further needs. project, which will collect the residual water Concerning all these services (power lines, from each scientific facility and discharge it in water, fuel, communications, etc.), ESO could a sewage treatment plant (that will be close to decide either, to conclude direct contracts with the future visitor centre). The treated water the supplier companies, or to do it through the will be eventually released into the fire system ORM community under adequate priority network of the island. conditions.
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First aid: A well equipped first-aid room in of data (as some scientific instruments can the ORM residence, an ambulance always generate). This is a supercomputer that is prepared, and coordination with local capable of high-speed data exchange, task authorities and medical services in case of distribution and resource optimization. La emergency. Taking into account that the Palma supercomputer contains 512 processors number of people working in the ORM would and provides a processing speed of 4.5 Tflops be doubled with the arrival of the E-ELT, the (which will be upgraded to 9 Tflops). In 2006, first aid services could be improved (i.e., this computer was ranked as the 413th fastest discuss the possibility to have permanent computer in the world. medical care in the residence). This supercomputer is one of seven nodes, Fire fighting: The ORM maintains always which form together the Spanish available a truck with a water pump that can Supercomputing Network (RES). This Net- be used in case of fire. The fire protection work, and its nodes, is under a permanent system will be shortly improved with the actualisation process. Indeed, IBM has installation of fire hydrants in each telescope. recently announced that a new supercomputer, This is part of the project, pending to be with a computing speed of 1016 operations per approved, to canalize water supply. second (100 times faster than the current main node of the RES), will be installed at the Heliports: In the Observatory, there are 4 Barcelona Supercomputing Centre, and heliports, which are sporadically used for operative from 2012. different official events. One of them must be always available to be used in case of Spain is willing to take an important role in the emergency. PRACE (Partnership for Advanced Computing in Europe) ESFRI project, and the RES will be Roads: There are two access roads to the part of it. This implies that the CALP Observatory. They are maintained under the supercomputing node will be kept updated and responsibility of the local authorities. A new competitive in the future, for the benefit of project to fully improve and adapt one of those Astronomy. roads, taking into account specific transport requirements as those for the E-ELT, is being currently performed by Cabildo de La Palma.
Sea level facilities: La Palma summits are one-hour drive from Santa Cruz de La Palma. As in other telescopes at the Observatory, this might enable part of the site operations (administration, etc) to be done at sea level and daily commuting of most of the personnel working at the mountain, both during construction and operations of the E-ELT
Supercomputing: The IAC sea level office (CALP, see picture above) also offers the scientific institutions a very interesting feature for the high speed processing of huge amounts
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Potential sites for the E-ELT and other ESO premises at La Palma ESO would be awarded full privileges, immunities and autonomy at these sites.
As previously mentioned, the site offered by A site of 100x100 m, for warehousing and Spain to ESO for the installation of the E-ELT other facilities, within 2-3km of the telescope, is located at the ORM. Other ESO premises is also available down hill from the ORM are also foreseen at the mountain and at sea- Residence. level. ESO will be awarded full privileges, immunities and complete autonomy at these A site for the proposed ESO 50-room sites. residence and a site for its canteen for 150 persons, including a 50 vehicle car park, is The graphic chart below shows some of the also foreseen near to and down hill from the potential sites of 300x200m for the telescope actual ORM Residence. As explained in a platform. These sites are: previous section, it would also be possible to LOC1: Area named Las Moradas; near GTC. enter into an agreement with the ORM for the extension of the existing Residence, according LOC2: Area located in between GTC and to ESO requirements and under adequate ORM Residence. priority conditions. LOC3: The MAGIC area next to the heliports An additional space of 20,000m2 for open LOC4: Area where WHT is currently located. storage is also available. There are two possible options: to create this space at the
beginning of the main road from SC to ORM, or in the area surrounding Garafía.
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Logistic advantages and social environment The geographical and socio-political situation of La Palma offers the best logistical and social advantages for the E-ELT. The geographical location of La Palma, as part La Palma is a quiet and peaceful island and of the European Union and close to mainland provides a very secure and safe environment, Europe, offers several advantages that would where people can enjoy a relaxed and high benefit the E-ELT construction and operation quality life. In fact, no robberies or assaults plans. have been recorded at the ORM after decades of operations, despite being in an isolated European Union Country: La Palma belongs location. to Spain and, consequently, is part of the European Union (EU). Moreover, the Canary Besides, Spanish labour law provides an Islands are one of its Outermost Regions, with environment of job security that guarantees the special benefits and advantages. The main protection of the workers, and the healthcare benefits resulting from being part of the EU system is of the high quality of EU can be summarized in the achievement of a requirements. It is also very relevant to peaceful and stable environment, one single mention here the existence of a same currency market (which allows free circulation of (the euro) with stable inflation indices always people and goods) and a major European commensurate with the rate of increase of influence in the world. This area of freedom, ESO’s budget, and allowing then a more security and justice provides an ideal robust and predictable estimate of the E-ELT environment to host and exploit a large and construction and operations budget. complex facility like the E-ELT. In particular,
Figure: Annual IPC variations during recent years in Spain (left) and Chile (right). IPC variations in Spain are between 2.7% and 3.8%, while, in Chile, inflation has experienced large variations with an important increment in the last 2 years (up to 10% in 2008).
Apart from the exemptions covered by the and affordable; the delivery of goods and Protocol on Privileges and Immunities, a services is easier, consumes less time and is special agreement exists to encourage the more economic; international staff could be astronomical research at the Canary Islands, in easily relocated to the island, and, finally, this such a way that astronomical instruments and convenient distance to Europe can help to components do not pay taxes in La Palma. stabilize the personnel and, therefore, to maintain the team expertise, which is quite La Palma is close to mainland Europe (and, important to ensure the quality of the operation therefore, to ESO HQ). A short distance brings and maintenance activities. advantages from different points of view: business and personnel trips are ergonomic
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The Human Development Report recently published for 2009 by the United Nations includes Spain in the position 15th of the list of the 38 countries world-wide with better GDP per capita, life expectancy and adult literacy rate (as a way to measure quality of live). No other E-ELT potential sites are included within this first-ranked list. La Palma summits are one-hour drive from Santa Cruz de La Palma (the capital of the island, which is located at the sea level). This distance allows daily commuting. Advantages for scientific visitors and for E- ELT staff: It is envisaged that the E-ELT will strengthen the already close links between ESO and academic Institutes in ESO member states. Therefore, taking into account the scientific character and activities that would be developed around the E-ELT, the advantages that the La Palma site (closer to mainland Europe) could provide for the mobility of scientists to the E-ELT site (and scientific and technical workshops) must be highlighted. People attracted by the idea of making a long- distance move also report that they fear the loss of contact and support from family and relatives. In the case of the ESO staff, and their families, that must be relocated during the E-ELT construction or operation, La Palma offers several advantages and a beautiful natural environment that can override these fears. International staff working on extensive campaigns at the mountain could find Transporting operational and maintenance convenient commuting to their home European goods and supplies: The short distance country after working periods. between mainland Europe and La Palma also provides logistic advantages from the point of Moreover, the short distance between La view of transporting goods and supplies. Small Palma and ESO Headquarters (in Munich) size packages can usually be sent by plane, brings an additional benefit that is the one- and bigger packages must be dispatched by hour only local time difference between both ship. The short distance from mainland Europe locations. Working hours in both places are results in time and cost savings. almost the same, which facilitates the communication between the teams located at ESO HQ and at the E-ELT in La Palma. A very enjoyable place to live: La Palma offers a very nice place to live. This can be both an attraction and way to retain the best human resources. The island enjoys pleasant temperatures in all seasons, warm in winter, not too hot in summer; provides a very attractive natural environment, with the possibility to enjoy a lot of different open-air activities; and posses all the infrastructure that people could need (national and international schools, hospital, medical centres, etc).
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LEGAL ISSUES Privileges and immunities Spanish authorities will guarantee ESO the applicability of privileges and immunities granted by the Protocol on P&I, and by an additional site agreement. Currently, Spain is developing the internal - to specify the land where ESO´s premises procedure in order to ratify the Protocol on the could be located, as well as the legal Privileges and Immunities of ESO. Fully regime of its ownership and other issues equivalent protocols have already been signed connected with this matter (connection with other International Organisations like when the premises are distributed, ESA or CERN. maintenance of the access points, etc.); So, if ESO decides to locate the E-ELT and - to guarantee the protection against light associated premises in Spanish territory, Spain pollution, mining and environmental would grant full regime of P&I applicable to conditions; the Organization. Moreover, a formal Site - to guarantee the full observing time is Agreement between ESO and Spain,would be available for ESO; formalized, according to usual practice when - specific issues about tax exemptions; an International Organization is located in - possibility for family of the members of Spain. The Site Agreement would specify the personnel to develop remunerated acti- applicability in this territory of the advantages vities in Spain.. granted to ESO by Spain, as signatory of the Protocol on P&I. This would be, therefore, a In order to implement properly the whole bilateral Treaty between ESO and Spain and, provisions of the Site Agreement, as well as of according to the Spanish regulations on the Protocol on P&I of ESO, the Spanish International Treaties of this kind, one of the Government would commit to inform closely official versions to be signed would be in all the Spanish authorities involved at the Spanish language, with equal effect to the different levels of decision (national, regional version signed in the ESO´s official language. and local) about the details of those P&I, in order to facilitate their smooth imple- Therefore, the Site Agreement would rule only mentation. Additionally a channel of direct the additional issues which are not covered by and close communication with ESO’s the direct application of Protocol on P&I, such Executive, with a view to solve any difficulty as: which could arise in the applicability of the P&I by any Spanish authority.
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Applicable Law and autonomy As an international organization, ESO is a sovereign legal entity, ruled by its own laws, respect to its members, activities and premises. Due to the fact that ESO is an International In relation with this issue, Spain would grant Organization, it is subject to its own to ESO the adequate support in order to ease regulations. That means ESO is a sovereign the connection and communication among its legal entity, which enjoys of immunity and premises, when these are located in distributed inviolability, being exempted from any points and, in some cases, when the roads or national laws or jurisdiction, and applying its points of access are of public use. The Site own internal rules to any matter. Therefore, Agreement would state the commitment of the and although the Protocol on P&I foresees this Spanish authorities to guarantee to ESO the issue, the Site Agreement between the free use of these accesses at any time, as well Organization and Spain would reflect this as to take the necessary measures when the point too, specifically for the premises located Organization would need a special use of these in Spain. accesses in certain circumstances (i.e., transportation of very large components). ESO is also sovereign with respect to the development of its official activities and fully The Site Agreement could state that, in case of responsible over its premises, being any matter that was not specifically ruled independent from any decision of the Spanish either by ESO´s internal regulations or by any authorities, as the Protocol on P&I and the Site other applicable international rules, the Agreement guarantees. Spanish laws would be applied to that matter. ESO will have full freedom for the development of its official activities in Spain.
Even more, Spanish authorities would be committed to facilitate this development.
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Availability of the land and ownership Spain will guarantee free and peaceful use of the land needed for ESO’s activities, as well as the ownership of its goods and rights. For the purposes of its official duties, Spain This special authorization of use conferred to would grant to ESO the land needed for the ESO by Spain will also constitute a right to be Organization to build and operate the E-ELT. inscribed in the Spanish Property Register, reinforcing the rights of ESO against any The entire ORM site is a public domain recall by third parties. property, under the responsibility of the Spanish government, and made available to In any case, within the borders of the land, the international scientific community through ESO will be entitled to build the facilities an Agreement on Cooperation in Astrophysics. needed for the development of its official activities, being the owner of them and, Article 132 of the Spanish Constitution states consequently, having the exclusive right of the law will rule the legal status of the public their usage and possession. domain property observing, among other mandatory principles, the inalienability. That However, ESO may acquire additionally any means the ownership of this public domain immovable property needed for its official property can not be transferred to other person activities, whose ownership shall be ruled by any legal title. Currently, the law in force according to the legal nature of the land (so, if on this matter is the Spanish Act 33/2003, on it is a private property, ESO may acquire the Property of Public Administrations. full ownership thorough the corresponding contract with the seller). Obviously, these So, taking into account that the main land additional properties shall enjoy the same would be located in an area of public domain privileges and immunities applicable to ESO. (ORM), it would not be possible to transfer its ownership to ESO. However, according to the At the end of the Site Agreement, and once Spanish rules in force, Spain would grant to ESO would have finished its official activities ESO, through the provisions of the Site in Spain: Agreement, a special authorization of use over a) Spain would have a right of option over the above mentioned land, free of payment and the movable or detachable material of with unlimited duration while the Site ESO in Spain, when ESO has no intention Agreement is in force. to take away; Furthermore, Spain will guarantee that there b) the conditions for the transfer of the fixed are not third parties’ rights or disputes with facilities to Spain would be defined in a those which might difficult the peaceful use of separate agreement. the land by ESO.
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Taxes ESO will be exempt of taxes in Spain in the terms applicable to the international organisations. Within the frame of the official activities of provisions of the regulations applied to ESO, its income, assets and other property, as diplomatic organizations accredited in Spain. well as loans and payments, would be exempt When the goods or services are sent or carried from taxes, whatever levied by Spain, its out from Spain with destination in other regions, provinces and municipalities, Member State of the European Union, the according to the terms applicable to the exemption of indirect taxes or duties would be international organizations, and in particular to granted according to the European Directives the regulations of the Protocol on P&I. in force, and when ESO provides to the ESO would be also exempt from the taxes and supplier, previously to the purchase, with the duties corresponding to registers and official form duly authorized. mortgages. The Site Agreement would detail the specific If ESO makes purchases or uses services of way and terms how these exemptions would substantial value, including the issue of be implemented observing, obviously, the publications, which are strictly necessary for provisions of the Protocol on P&I. the exercise of its official activities, in the Of course, as foreseen in the Protocol of P&I price of which indirect taxes or duties are of ESO, its staff would be exempt from included, Spain would, where these indirect taxation in Spain on the salaries, emoluments taxes or duties are identifiable, provide for and benefits paid to them by ESO. their reimbursement in accordance with the Construction support and building permits Spain will facilitate to ESO the appropriate support for construction and building permits. In the Site Agreement, Spain would commit to to be accompanied by an Environmental make all the efforts in order to grant to ESO Impact Study and a Safety and Health study. the permits for the construction in its premises These accompanying documents are produced of the buildings and facilities needed for its by the team of experts responsible for the activities, as it is usual with other International plans. Organizations located in Spain. Once the professional colleges of architect and It is worthy to mention here that main public technical draftsmen have endorsed them, they authorities and other stakeholders in La Palma have to be presented to the Garafía Council. and in Spain have shown their interest and From this point, this administration will guide formal support to the installation of the E-ELT solely the whole process up to the approval of in this Island (Appendix 2). This is of extreme the licence to commence the building work. relevance since it will allow all permits for the construction of the E-ELT and other ESO’s In this sense, Garafía Council will submit premises to be granted in a very short time these building and installation plans to the La scale. Palma Cabildo (island government), to obtain the appropriate Land Designation ruling. With respect to the necessary permits and processes related to the building of the E-ELT Garafía Council will submit also the project to and its auxiliary facilities in La Palma, these the Caldera de Taburiente National Park Board could be summarized as follows: and to the Regional Government Ministry of the Environment for their review and a Building and installation Projects: Compe- recommendation regarding the project. tent experts have to draw up the plans for the building works and installations. These two The whole process in obtaining licenses to plans should include a description about what start the work has been normally around 6 is intended to build and to install, justification, months in total for the last facilities erected at location, characteristics of the site proposed, the ORM site. basic and special needs, etc. Both plans need
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Appendix 1: Science with the E-ELT in the Northern Hemisphere All top-level science goals for the E-ELT can be attained from both hemispheres. Synergies with other ESO facilities can be realised from La Palma too.
E-ELT Synergy with other facilities d) Large facilities are not survey facilities and and sensitivity with the hemisphere are normally not used as finders for other large facilities. The E-ELT represents the most important step We can briefly illustrate these cases, for forward within the future astronomical example using ALMA. ALMA has an angular infrastructures by itself, and therefore the E- resolution similar to the E-ELT (when ELT alone has to be the first priority when operating in AO mode) and covers a different taking decisions about its design, wavelength range. It is probably the facility instrumentation or location. Nevertheless, it most commonly considered for synergies with will benefit from previous works (like present the E-ELT. Recognizing the interest of this day 8-10m telescopes) and complementarities synergy, point (a) indicates that it will be with other facilities. Therefore, possible interesting to observe the same object with synergies of the E-ELT with present or future both facilities only if the SED is adequate for facilities and surveys (ground based or space observation with both of them. For sources borne) are important as something that may with strong SED slopes (i.e., much brighter at increase the scientific outcome of the submillimeter wavelengths than at optical- telescope. The presence of these facilities or near-IR or vice versa) one of the facilities may the availability of previous observations in one be blind. or the other hemisphere may imply a difference among them. Besides, the synergy between ALMA and the E-ELT is used sometimes as an argument to However, synergies among different facilities conclude that the E-ELT should be located at are not easy to foresee. A clear example of the approximately the same latitude as ALMA. difficulties arising is given by the ESO-ESA However, point (b) indicates that the agreement on the ESO-XMM programme, exploitation of such synergies is much more which grants VLT and XMM-Newton obser- flexible. With the E-ELT located in the NH vations from either ESO or ESA. The (e.g., the ORM), both facilities (ALMA and E- programme has a ceiling of only 400 ELT) still share a significant fraction of the kiloseconds per year each side, but it really sky. If we restrict observations to air masses never saturates. The following general points less than 1,5, the ORM and Chajnantor still have to be emphasized when we try to study share a declination range of 50º in the sky the possible synergies between two different (declinations from -22º to +27º). Looking at facilities. air masses less than 2, the common covered a) If two facilities cover different sky is 70º (from declination +37º to -32º), wavelengths, then the possible synergy will which means that there is a large overlap in the depend on the Spectral Energy Distribution sky for most of the objects distributions. The (SED) of the considered objects and figure below illustrates this point for all known facility sensitivity. class 0 protostars. b) Two facilities located at different latitudes This figure can also be used to illustrate point may still share an appreciable fraction of (c). If we are interested in a particular object in the sky. the Figure, it may be observable or not both with ALMA and the E-ELT located in the c) There should be a clear distinction between north hemisphere. However, if we are the case posed by a specific target and the interested in the science of Class 0 objects, it is general science case. clear that there are enough overlapping cases. Of course, a given object is always a particular case.
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Plateau de Bure, the 40-m Yebes antenna or the Giant Millimeter Telescope in Mexico (all in the North) offer excellent possibilities for the E-ELT in this context, complementing the wavelength range towards mm wavelengths. One of the most interesting synergy possibilities is that offered by dedicated survey facilities, as it will be the case of VISTA (Paranal). In the Northern hemisphere we may cite SCUBA-2 at the JCMT, UKIDSS from the UKIRT and Pan-Starrs, all in Hawaii. While VISTA and UKIDSS use NIR observations and Pan-Starrs observes in the optical, SCUBA-2 is a particularly interesting possibility because it covers the sub-mm range. All these surveys are providing or will Figure 1. Distribution in the sky of known class 0 starts, provide enough interesting targets for the E- showing the maximum range in the north for ALMA and the maximum range in the south for La Palma and Mauna Kea. ELT. The area of the circles is proportional to the distance to the source. The lines correspond to air masses equals to 2,0. This Cosmological surveys and fields are available figure is provided by D. Barrado Navascués (Centro de in both hemispheres, including several Astrobiología, INTA). equatorial ones, although some of them are accessible only from the North (e.g., the For example, we can assume that we are Lockman Hole or the Groth Strip) or from the interested in studying irregular metal-poor South (e.g., the Chandra Deep Field South). dwarf galaxies. There are examples in both Nevertheless, the E-ELT will benefit from hemispheres. But if we are interested in most of this previous work, whatever location observing the Magellanic Clouds, this can only is chosen. be done from the South. By the contrary, if we are interested in resolving the stellar In the era of the E-ELT, present 8-10 m-class population of large spiral galaxies, there are telescopes may play an important role as again examples in both hemispheres. But if we auxiliary facilities. Europe is in an excellent want to observe M31, this can only be done situation here, as it has access (either global or from the North. by individual countries with which agreements may be possible) to VLT and Gemini-S in the Point (d) finally emphasizes the issue that only South, and GTC, Gemini-N and LBT in the a few selected targets, chosen by its particular North. We would also like to mention here the interest (and not necessarily known a priori) wide-field camera SuprimeCam at the Subaru will be observed with both facilities. It will be (Hawaii) and the Large Synoptic Telescope difficult to construct a complex science project (Cerro Pachón) that will provide the possibility on the basis of the synergy between two large of large surveys with 8-m class telescopes. facilities. Space-based facilities are usually not linked to Therefore, the ALMA-EELT synergy will any hemisphere, although sometimes, like in depend on the particular conditions of the the case of the Kepler satellite, the target field science case considered. As general rule, the is limited to one of them (in the case of same will be true for any other facility. Kepler, a northern field). Apart from present Other facilities offer as well the possibility of a and new satellites like Spitzer and Herschel, synergy with the E-ELT. In the radio domain, the largest interest will be in the satellites that SKA in the South, or EVN, e-EVN (and VLA, will probably operate during the time of E- e-VLBI) in the North offer also excellent ELT. Gaia will map the Galaxy with possibilities, even reaching (expectedly) better unprecedented accuracy and the World Space sensitivity and angular resolution than ALMA, Observatory will provide a UV complement to this time at cm wavelengths. the E-ELT. Finally the JWST and the E-ELT are expected to complement each other in a Smaller facilities on the other hand can collect similar way as the HST and the 8-10 m-class a large number of objects, from which the telescopes have been doing for more than 15 most interesting ones can be then observed by years. The ultra-sensitive NIR and mid-IR the E-ELT. The 30-m IRAM telescope and the JWST instruments will discover objects planned Northern Extended mm Array in requiring detailed high angular resolution
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La Palma as the European Site for the E-ELT follow-up observations with ELT. Other detection in nearby stars and in the young observing capabilities of ELT and JWST (e.g. stellar clusters Hyades and Pleiades, exo-Earth R, spectral coverage, PSF stability, etc) will follow-up characterization of transiting planets also be highly complementary. with emphasis in detection of bio-markers and also studies of low-mass stars in nearby star We conclude that many facilities, at many forming regions. They also discussed E-ELT different wavelengths and spectral or spatial research on our own Solar System with focus resolutions and located in both hemispheres on the largest trans-neptunian objects known will be an excellent complement for the E- as well as studies of nearby stars with proto- ELT. Which one of them offers the best planetary disks. As an example, the E-ELT possibilities depends on the particular science would allow the detailed characterization, case. The same can be said for the selection of possibly including biomarkers, of the a given hemisphere. Although our individual atmosphere of planets similar to the Earth. pet object may be only accessible from one of While general science cases can be addressed them, general science cases can be equally from both hemispheres, the favourable addressed from both hemispheres. conditions of the Pleiades and Hyades clusters and the selected field of view of the Kepler satellite turn the northern hemisphere more First-level science suitable for certain topics. A meeting on "Science with the E-ELT from The local universe: This session included 11 the Northern Hemisphere” was held in Madrid presentations, which could lead to one or more the 16th and 17th of April 2009, to promote the observing proposals each. From the titles of involvement of the Spanish astronomical the presentations alone it can be concluded community in the definition of scientific that three objects unique to the Northern programs for the E-ELT and, also, to Hemisphere are of particular interest to the encourage the possibility of locating this large Spanish astronomical community, namely the infrastructure in the Northern Hemisphere. The two Local Group spiral galaxies M31 and meeting included several sessions to discuss M33, and the Coma Cluster. M31 and M33 are specific scientific proposals that could be the closest galaxies to the Milky Way and they performed by the E-ELT located in the NH, to are the kind of similar galaxies to ours that can study in more detail the sensitivity of the teach us much about the structure of the Milky hemisphere and to contribute defining the Way. For example, it is possible to compare cutting edge science that can be made with the the properties of the supermassive black hole E-ELT. in M31 with the centre of our galaxy. In other cases, candidate objects could be found in both The scientific cases discussed during the hemispheres, although even in such cases key meeting that could be preferably done from the preferred objects were located at positive Northern Hemisphere were addressed as a declinations. complement and not raised as a competition or confrontation to the cases that could be Galaxies and cosmology: 7 contributions preferentially addressed from the Southern were presented in this session. The general Hemisphere. Because of the ESO tradition and scientific cases are insensitive to the long previous work in the southern hemisphere because of the large-scale isotropy hemisphere, it is felt that the science cases of the far Universe and the existence of considered until now by the ESO community cosmological fields of interest both in the could be biased towards the south. This Northern and Southern hemispheres, as can be meeting tried to contribute to balance this bias seen in the Table below (courtesy of P. Pérez and to show that both hemispheres offer plenty González, Univ. Complutense de Madrid). of interesting science cases and previous Green colours indicate favourable conditions, preparatory work that merit the strong impulse red colours mean that observations are not that will represent a telescope like the E-ELT. possible and light yellow colours indicate intermediate conditions. Starts and planets: This session included half a dozen presentations that covered exoplanet
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Field ORM, Morocco Chile, Argentina
FIR Hrs / Usable Seeing Hrs / Usable Seeing night nights night nights Lockman 10h Feb 67% (7h) 1,1” 0h - -
GOODS-N 10h Mar 70% (7h) 1,0” 0h - -
EGS 8h Apr 74% (6h) 0,7” 0h - -
SXDS 6h Nov 60% (4h) 0,8” 8h Nov 85% (7h) 1,0”
GOODS-S <3h - - 8h Nov 85% (7h) 1,0”
COSMOS 7h Feb 67% (5h) 1,1” 7hFeb 85% (6h) 0,9”
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Appendix 2: List of Public Authorities and stakeholders in Spain formally declaring their support for the installation of the E- ELT in La Palma This favourable position from local, regional and national administrations and entities would have a very positive impact in the implementation of the project.
Institution Date of formal decision
The Canary Islands Socio-economic Council (Consejo Económico y Social de Jun 2007 Canarias; an independent consultant body of the Canary Islands Regional Government)
National Commission for Astronomy (Comisión Nacional de Astronomía) Jan 2008
La Palma Cabildo (island government) Oct 2008
Santa Cruz de La Palma Council (city council) May 2009
Confederation of Spanish Industry – Regional delegation (S/C Tenerife) (CEOE - May 2009 Confederación Española de Organizaciones Empresariales de S/C de Tenerife)
Confederation of Spanish Industry (Confederación Española de Organizaciones Jun 2009 Empresariales)
The Tenerife Cabildo (island government) Jun 2009
The Canary Islands’ Engineering Cluster (Cluster de Ingeniería de Canarias) Ago 2009
The Spanish Senate Oct 2009
La Villa de Garafía Council (city council) Nov 2009
The Canary Islands’ Regional Parliament Nov 2009
Other entities at regional and national levels are drafting formal proposals to endorse this initiative, expressing full support and interest on the installation of the E-ELT in La Palma.
26 / 26 Appendix 2: Public Authorities and stakeholders