We have searched for possible sites in Argentina for the installation of
large air Cherenkov telescope arrays and water Cherenkov systems. At present
seven candidates are identified at altitudes from 2500 to 4500 m. The highest
sites are located at the Northwest of the country, in La Puna. Sites at 2500
and 3100 m are located in the West at El Leoncito Observatory, with excellent
infrastructure. A description of these candidate sites is presented with
emphasis on infrastructure and climatology.Comment: Submitted to Proceedings of "4th Heidelberg International Symposium
  on High Energy Gamma-Ray Astronomy 2008

A. C. Rovero

A. Etchegoyen

B. Garcia

D. Garcia-Lambas

E. Colombo

Felix A. Aharonian

Frank Rieger

G. E. Romero

H. Levato

H. Muriel

I. Allekotte

M. C. Medina

P. Recabarren

Werner Hofmann

X. Bertou

English

arXiv

Crossref

Sites for Gamma-ray Astronomy in Argentina

We have searched for possible sites in Argentina for the installation of large air Cherenkov telescope arrays and water Cherenkov systems. At present seven candidates are identified at altitudes from 2500 to 4500 m. The highest sites are located at the NW of the country, in La Puna. Sites at 2500 and 3100 m are located in the West at El Leoncito Observatory, with excellent infrastructure. A description of these candidate sites is presented with emphasis on infrastructure and climatology.Fil: Rovero, Adrian Carlos. Consejo Nacional de Investigaciónes Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomía y Física del Espacio; ArgentinaFil: Romero, Gustavo Esteban. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Instituto Argentino de Radioastronomía. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto Argentino de Radioastronomía; ArgentinaFil: Allekotte, Ingomar. Comisión Nacional de Energía Atómica; ArgentinaFil: Bertou, Xavier Pierre Louis. Comisión Nacional de Energía Atómica; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Colombo, E.. Comisión Nacional de Energía Atómica; ArgentinaFil: Etchegoyen, Alberto. Comisión Nacional de Energía Atómica; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Garcia, Beatriz Elena. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Tecnología en Detección y Astropartículas. Comisión Nacional de Energía Atómica. Instituto de Tecnología en Detección y Astropartículas. Universidad Nacional de San Martín. Instituto de Tecnología en Detección y Astropartículas; ArgentinaFil: Garcia Lambas, Diego Rodolfo. Universidad Nacional de Córdoba; ArgentinaFil: Levato, Hugo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Juan. Complejo Astronómico "El Leoncito". Universidad Nacional de Córdoba. Complejo Astronómico "El Leoncito". Universidad Nacional de la Plata. Complejo Astronómico "El Leoncito". Universidad Nacional de San Juan. Complejo Astronómico "El Leoncito"; ArgentinaFil: Medina, Maria Clementina. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Instituto Argentino de Radioastronomía. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto Argentino de Radioastronomía; ArgentinaFil: Muriel, Hernan. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Astronomía Teórica y Experimental. Universidad Nacional de Córdoba. Observatorio Astronómico de Córdoba. Instituto de Astronomía Teórica y Experimental; ArgentinaFil: Recabarren, Pablo Genaro Antonio. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Astronomía Teórica y Experimental. Universidad Nacional de Córdoba. Observatorio Astronómico de Córdoba. Instituto de Astronomía Teórica y Experimental; Argentina4th International Meeting on High Energy Gamma-Ray AstronomyHeidelbergAlemaniaMax-Planck-Institut für Kernphysi

Rovero, Adrian Carlos

Romero, Gustavo Esteban

Allekotte, Ingomar

Bertou, Xavier Pierre Louis

Colombo, E.

Etchegoyen, Alberto

Garcia, Beatriz Elena

Garcia Lambas, Diego Rodolfo

Levato, Hugo

Medina, Maria Clementina

Muriel, Hernan

Recabarren, Pablo Genaro Antonio

CONICET Digital

Sites for Gamma-ray Astronomy in ArgentinaA.C. Rovero∗, G.E. Romero†, I. Allekotte∗∗, X. Bertou∗∗, E. Colombo‡,A. Etchegoyen‡, B. Garcia§, D. Garcia-Lambas¶, H. Levato‖, M.C. Medina††,H. Muriel¶ and P. Recabarren¶∗Instituto de Astronomía y Física del Espacio (CONICET-UBA), CC 67, 1428, Cdad. de Buenos Aires, Argentina†Instituto Argentino de Radioastronomía (CCT-LP, CONICET), CC 5, 1894, Villa Elisa, Buenos Aires, Argentina∗∗Centro Atómico Bariloche and Instituto Balseiro (CNEA and UNCuyo), 8400, Bariloche, Rio Negro, Argentina‡Laboratorio Tandar (CNEA), Av. Gral. Paz y Constituyentes, Buenos Aires, Argentina§Universidad Tecnológica Nacional, Facultad Regional Mendoza, Rodríguez 273, 5500, Mendoza, Argentina¶Instituto de Astronomía Teórica y Experimental (CONICET-UNC), Laprida 854, 5000, Córdoba, Argentina‖Complejo Astronómico El Leoncito, CC 467, 5400, San Juan, Argentina††Laboratoire de l’Univers et ses Théories, Obs. de Paris, 5 Place Jules Janssen, 92195, Meudon Cedex, FranceAbstract. We have searched for possible sites in Argentina for the installation of large air Cherenkov telescope arrays andwater Cherenkov systems. At present seven candidates are identified at altitudes from 2500 to 4500 m. The highest sites arelocated at the NW of the country, in La Puna. Sites at 2500 and 3100 m are located in the West at El Leoncito Observatory, withexcellent infrastructure. A description of these candidate sites is presented with emphasis on infrastructure and climatology.Keywords: Site search, Site testing, Ground-based gamma-ray astronomyPACS: 95.45.+i, 95.55.Ka, 95.85.PwINTRODUCTIONAfter successful operation of Cherenkov telescopes, likeHESS, MAGIC and VERITAS, the scientific communityis beginning to seek for sites to locate a new generationof instruments. Not only air Cherenkov but also waterCherenkov detectors are expanding frontiers. HAWC isbeing constructed in Mexico and would require a coun-terpart in the Southern Hemisphere. At smaller scale,LAGO has been expanding from Auger, in Argentina, toBolivia, Mexico, Venezuela and Perú, seeking for highaltitude sites to install single water Cherenkov tanks.For galactic gamma-ray astronomy the observationfrom a Southern Hemisphere location has obvious ad-vantages as the most important portion of the GalacticPlane is seen from the South, including the Galactic Cen-ter. For extragalactic gamma-ray astronomy, a homoge-neous distribution of instruments should be spread overthe World, especially for monitoring of transient sources,like AGNs, which require a complete time coverage (RAcoverage). In the Northern Hemisphere the distributionof air Cherenkov telescopes is such that this could beachieved. The lack of telescopes in South America, how-ever, prevents the correct time coverage for the SouthernHemisphere. For water Cherenkov detectors this problemis attenuated by their large angular acceptance.Requirements for gamma ray detectors are wide. Forwater Cherenkov, high altitude and water availabilityhave to be considered. For air Cherenkov, moderate al-titudes, atmospheric transparency and low cloud cover-age are required. In any case, good infrastructure andlocal support are desired. In South America moderateand high altitude sites are located in "La Puna" and itssurroundings. This region extends from the NW of Ar-gentina, up to the North of Chile, West of Bolivia andSW of Perú. In this area the cloud cover improves to-ward the SW so only the North of Chile and NW ofArgentina would be available for Cherenkov telescopes.In Chile there are several Observatories with optical, in-frared and millimetric telescopes. The ALMA array isbeing deployed and might extend its aperture by locat-ing a single dish in Argentina [1]. On the East of LaPuna, in Argentina, there are sites being characterizedfor Extremely Large Telescopes (ELT) by a local group(for ESO). Optical (CASLEO: www.casleo.gov.ar), Ra-dio (IAR: www.iar.unlp.edu.ar) and cosmic-ray (Auger:www.auger.org) observatories are operating in the coun-try, with an important academic community.In the last two years we have been searching for sitesin Argentina that fulfill conditions for both water and airCherenkov detectors. Here we report on such searches.EXPLORED REGIONSTo seek for a flat land of ∼1 km2 at more than 2500 me-ters above sea level (masl) with clear skies in Argentina,the Central and NW regions of the country have to bearXiv:0810.0628v1  [astro-ph]  3 Oct 2008considered. In Figure 1 a search for 1 km2 sites at differ-ent altitudes is shown [2]. So far we have searched twosubregions, one at high altitudes on the North and an-other at moderate altitudes on the South (see Figure 1,right). The northern region is part of La Puna, a land atmore than 3500 masl. In Argentina this region is locatedto the East of the Andes mountains, on the provinces ofJujuy, West of Salta, and North of Catamarca. The regionat moderate altitudes extends to the South of La Puna, onthe West of the provinces of La Rioja, San Juan and Men-doza. In the following sections we report on two searchedregions, the northern portion of La Puna and the NationalReserve of “El Leoncito”, in San Juan.FIGURE 1. Explored regions in Argentina. Left: Search for 1 km2sites [2]. Square: Auger Southern Observatory (1400 masl); cross:former candidate site for SKA (2600 masl), 12 km North of El LeoncitoAstronomical Observatory. The enclosed area is enlarged on the right.Right: province limits in the Center and NW of the country. Theexplored region enlarged in Figures 2 and 3 are indicated.HIGH ALTITUDE SITES: LA PUNAA map of the northern explored region is shown in Figure2. La Puna is climatologically classified as a highland cli-mate. It has low temperatures, poor vegetation, and a lowannual precipitation with a dry winter. It extends alongthe leeward slopes of the Andes where winds are dom-inated by the Pacific high pressure system (subsidence).Advection from the Pacific causes a predominant windfrom the West which is the main control of climate inthe whole Puna [3]. A roughly similar West-East regimeexists for rainfall, humidity and cloudiness.As an example, we can cite meteorological data fromtwo stations. One is near Susques, at 3675 masl, and thesecond is La Casualidad (25:03 S, 68:13 W), located at4092 masl, 300 km SW of Susques. From Susques wehave data from 1972 to 1990 (Dirección de Hidráulicade Jujuy), only on precipitation and temperature: aver-age annual total rainfall is 184 mm (mainly in summer)and average temperature is 7.6 Celsius. From La Casu-alidad we have ten years of data from 1963 to 1972 [4]:annual averages are: wind: 26% calm, 55% from West(28 km/h), 13% from NW (22 km/h) and 5% from SW(24 km/h); Sky coverage: 22 days; humidity 33%; temp.:3.9 Celsius; low temp.: - 4.1 Celsius; frost: 267 days; to-tal rainfall: 37 mm in 6.3 days; snow: 2.8 days.By analyzing historical climate data, Schwerdtfeger[3] shows that cloudiness is another variable that seemsto show roughly the same West-East behaviour in LaPuna. Dedicated studies have been done by the IATEgroup in their search for ELT [5] and by Erasmus [6]for the ALMA project using satellite images. Resultsfrom these analyses are all coherent with each other. Theresult on sky cover shown by Schwerdtfeger indicatesthat the isoneph of 20% is right to the East of the wholeregion studied by both Erasmus and IATE. All of themindicate that cloudiness decreases toward the West. Forthe selected sites in Figure 2 we note that the sky coverconditions are similar in average (≈ 85% of clear nights),except for Mina Aguilar (5) which is more into thecloudy skies. However, if a seasonal analysis is done, thenorthern sites, (2) and (3), have larger variations than theother two locations in the South, (1) and (4), being betterin winter and worse in summer.FIGURE 2. Road map of the northern area indicated in Figure 1.Arrows point the locations selected as candidate sites: (1): Salar dePocitos; (2): El Porvenir; (3): El Taire; (4): Alto Tocomar and (5):Mina Aguilar. The cross shows the chosen position for ELT beingcharacterized by the IATE group: Tolar Grande. Squares indicate theposition of nearby cities with daily flight connections to Buenos Aires.This region has two major cities with internationalairports and daily flights to Buenos Aires. San Salvadorde Jujuy (pop. 250,000) and Salta (pop. 500,000). Theyhost their national universities: U. de Jujuy (≈10,000students) and U. de Salta (≈20,000 students). Two townsare identified in this area, Susques and S.A. de los Cobres.Susques (23:23:12 S, 66:21:47 W) is a small town(pop. 2000) at 3675 masl. It takes 2.5-3 hours ridefrom Jujuy city (202 km) driving on a very nice pavedroad that connects to the West with Antofagasta (Chile),through the border point “Paso de Jama” (4400 masl).There are two good hotels in Susques both located onthe National Route 52 at 3700 masl: “Hotel Unquillar”(www.elunquillar.com.ar) and “Hotel Pastos Chicos”(www.pastoschicos.com.ar), with an overall allocation of60 beds in 20 rooms at≈ u$s30 (single rate). Satellite TVand regular and cell phone services are available.San Antonio de los Cobres (SAC) (24:13:30 S,66:19:10 W) (pop. 3000) is at 3775 masl. From Salta cityit takes 2.5 hours (164 km) driving on the National Route51, which is 75% of the way a paved road. Route 51 con-tinues as gravel road to the West to connect with Chileat “Paso Sico” (4092 masl). There is one good hotel intown, “Hotel de las Nubes”, which has approximately 25beds in 10 rooms at a similar rate of Susques. SatelliteTV and regular and cell phone services are available.Identified candidate sitesTolar Grande: Astronomers from IATE are character-izing this site for the location of ELT (ESO). Their cho-sen point is in the Macón mountain range, 25km Eastof Tolar Grande (24:38:49 S, 67:20:14 W) at 4600 masl.There are several experiments being carried out there tocharacterize the sky. This led us to consider Tolar Grandeas a reference site, where flat lands at ∼4000 masl canbe found. It takes 3.5-4 hours to get there from SAC andthere is a nice lodging house at low rates.Salar de Pocitos: 80 km SW of SAC we have iden-tified a candidate site nearby the small neighborhood ofSalar de Pocitos, where no significant infrastructure isavailable except electricity, water and phone connection.It takes 2-2.5 hours drive from SAC (140 km) on a verynice gravel road to get there. The site is a very extendedplain at 3750 masl (slope ≈0.01), limiting with a moun-tain range to the West and a salt land to the East, 5 kmWest of route 27 (24:26:40 S, 67:06:10 W). Ground iscompact and vegetation is very poor. There is a railroadcrossing the field. The salt land on the East should notcontribute with aerosols as wind is mainly from the West.El Porvenir: Few km South from the intersection ofroutes 52 and 70, we identified a possible site at 3950masl (23:38:30 S, 66:46:30 W). From there, it takes 40minutes drive (65 km) on the paved route 52 to getSusques, where a base of operation could be located.There are ≈5 km of flat plain from route 70 beforereaching the mountain range on the West. There is alsoa salt land to the East which should not contribute to theair aerosol content as wind is mainly from the West.El Taire: This is a site specially identified for waterCherenkov systems (23:23:41 S, 66:31:27 W). It is at4150 masl closeby route 52, 20 km West of Susques.There is a stream of spring water and perforation is ageneral practice to get water from underground.Alto Tocomar: This is the highest plain we have iden-tified (24:12:00 S; 66:30:30 W). It is 25 km West of SACat 4500 masl, closeby route 51, with nearby summits ofmore than 5000 masl and several km2 of flat land. Thereis a railroad crossing the site and few spring water pointshave been localized at the western border.Mina Aguilar: Another excellent site for waterCherenkov systems (23:09:03 S, 65:42:55 W). It is at3900 masl, nearby a small town with all supplies neededfor operations, including stores and hospital. A site at5100 masl is easy to access by vehicle in 20 min. drive.MODERATE ALTITUDE SITESFIGURE 3. Road map of southern area indicated in Figure 1. Ar-rows point candidate site locations: (1): Naranjo; (2): Tontal. Squares:position of nearby cities with daily flights to Buenos Aires.El Leoncito Astronomical Observatory (CASLEO:Complejo AStronómico el LEOncito) (31:48:00 S,69:17:30 W) is an astronomical facility located at 2600masl in the province of San Juan, with offices and labo-ratories in the city of San Juan. In Figure 3 we show theroad map of the area. The Observatory is placed insidea reservation area of 416 has. dedicated to astronomy,which is part of the National Park “El Leoncito”, a70,000 has. natural reserve. There are two major citieswith daily connection to Buenos Aires, San Juan (pop.450,000), and Mendoza (pop. 900,000). These two citiesare the host of their national universities: U. de San Juan(≈20,000 students), and U. de Cuyo (≈38,000 students).There is a small town, Barreal (pop. 2500), 40 km NW(30 min. drive) of the Observatory where basic suppliesare available. Regular transportation to the mountainis organized by the Observatory staff several times perweek. It takes 3.5 hours to get from San Juan to theObservatory (250 km) on a good paved road, throughCalingasta and Barreal. One alternative for internationaltravelers is to flight to Santiago (Chile), connect toMendoza and take a rented car to reach the site throughUspallata. It also takes 3.5 hours to get from Mendozacity to the Observatory (230 km), mostly on paved road.The most distinctive feature of a site in this area isthe Observatory infrastructure. After more than 20 yearsof operation the site has everything needed for operatingand maintaining any running instrument on the moun-tain. A 13.2 KV power line, an emergency generator,internet (25 Mbps) and regular and cell phone servicesare available. There are on the mountain mechanical andelectronics workshops, a liquid nitrogen plant and a 2.15m mirror coating chamber. The lodging facilities includebedrooms with private toilets for 45 people and a diningroom for the same number. More than ten people fromthe staff are permanently at the site for maintenance,cleaning, cooking and to attend visitors.The Observatory has its own meteorological sta-tion (www.casleo.gov.ar/weather/leonci_weather.htm).Monthly values for the last ten years are: mean tem-perature: 5.5 C (July) and 17.5 C (January); maximumtemperature: 20.3 C (June) and 30.5 C (January); rel.hum.: 27-43 % along the year; rainfall: 11-18 mm(December-March) and 2-7 mm (April-November);wind speed: 4.5-8.4 km/hr, mainly from SW (55 %) andfrom SE (30 %); maximum wind speed: 62-88 km/hralong the year; hail: 1-2 days/yr; frost: none; lightning:6-8 days/yr; maximum snowfall: <30 cm.Analyzing more than 20 years of operations the Ob-servatory has 270 observing nights per year (74 %), fromwhich 100 nights are photometric (more than 6 hr of per-fect sky conditions). Sky brightness has been measuredin magnitudes per square arcsecond: U = 22.1, B = 23.3and V = 22.7. For comparison, these values are similar tothose at Cerro Tololo Inter-American Observatory (fromCTIO), Chile: U = 22.0, B = 22.7 and V = 21.8.In an attempt to connect both the northern and south-ern studied regions, the IATE group analyzed 1.5 yearsof GOES images (1998-1999) of both El Leoncito andLa Puna. The uncertainties of this study are unknown butgood enough to say that between site candidates on theNorth and South there is a difference of ≈ 10% in skycoverage, being the northern sites better and characteriz-ing El Leoncito with ≈ 75% of clear nights.Identified candidate sites at El LeoncitoTontal: To the West of the Tontal range there is aplain of at least 5×10 km2 at 3000 to 3500 masl. Wehave pointed to a specific site at 3130 masl (31:48:12S; 69:10:31 W), located ≈ 15 km to the East of theObservatory. Once in the site, accessibility is very good.Naranjo: To the North of the Observatory on the Westof El Naranjo range there is a site of similar characteris-tics of Tontal but with slightly smaller slope. The markedlocation is at 2590 masl (31:43:52 S; 69:16:20 W). Thissite was the former SKA candidate site. It is very easy toaccess from the Observatory by a 20 min. drive (10 km).Ground is compact assuring accessibility.FINAL COMMENTSWe have searched for candidate sites for ground-basedgamma-ray astronomy in two regions of Argentina: anorthern region, in La Puna, and a southern one, nearbythe El Leoncito Astronomical Observatory. In La Punawe have found five candidate sites at altitudes from 3750to 4500 masl, being the ones on the SW better suited forair Cherenkov detection, as there are ≈ 85 % of clearnights. Sites near the town of Susques (El Taire and ElPorvenir) have very good accessibility and reasonable in-frastructure. The highest site (Alto Tocomar) is 25 kmfrom San Antonio de los Cobres, where a base for op-erations can be mounted. The lowest site in the area,Salar de Pocitos, is the best candidate for air Cherenkovalthough infrastructure is rather poor. The northeasternsite, Mina Aguilar, has all needed for water Cherenkovsystems but is too far into cloudy skies for air Cherenkovdetectors. Earthquake risk is moderate in La Puna. AtEl Leoncito we identified two sites at 2590 and 3130masl. El Leoncito Observatory has been operational for20 years and has excellent infrastructure including lodg-ing, power, internet, phone, food, mechanical/electronicsworkshops, regular transportation, etc. It has ≈ 75 % ofclear nights. Earthquake risk is of some importance butsimilar to other astronomical observatories.Acknowledgments: We are grateful to Olga Penalba forinformation on climatology and the local SKA group forsite information. The work at IATE is being supported byESO. The following authors are members of CONICET:ACR, GER, XB, AE, BG, DGL, HL, HM and PR.REFERENCES1. I.F. Mirabel, personal communication.2. S. Fegan, in Towards a future ground-based gamma rayobservatory. October 20, 2005, Malibu, California, USA.3. W. Schwerdtfeger, “Climates of central and SouthAmerica,” in World Survey of Climatology, Vol. 12,Elsevier. Amsterdam, Oxford, New York, 1976.4. SMN (Servicio Meteorológico Nacional, Argentina), in N.Estadística Climatológica 35, Serie B, FAA, 1961-70.5. P. Recabarren, et al., Ast. and Space Sci. 290, 409 (2004).6. D.A Erasmus, “An analysis of cloud cover and watervapor for the ALMA project,” in www.eso.org/gen-fac/pubs/astclim/espas/radioseeing/, 2002.

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