Bearing in mind the relatively high wind speed measured in the Macon area, that may prevent the use of the radiotelescope for a sizeable fraction of time along the year, a new place to harbour LLAMA was looked for. Furthermore, considering that in the future LLAMA may be used to carry out VLBI experiments with some of the antennas installed in Chilean soil, it would be desirable to find a high altitude place on the Argentinean side located at least 100 km away from those antennas in order to increase the angular resolution that could be achieved in those VLBI experiments. With these basics ideas in mind, the region of Alto Chorrillos (4800 meters above sea level) was selected. In this region an instrument, the tipper, to characterize the atmospheric transparency at mm wavelengths was erected (see Figure 1). Along with this instrument, a weather station was also installed in order to monitor the local weather conditions.
|Figure 1: Panoramic view of the Alto Chorrillo region, located at 4800 meters above sea level. The radiometer and accessories to measure the atmospheric opacity are shown. The collected datasets are sent on a daily bases to IAR, for further analysis, using a satellite link.
|Figure 2: Atmospheric opacity measures statistics obtained by the radiometer in the Alto Chorrillo region.
This site was selected due to its low atmospheric opacity at mm wavelengths. Figure 2, represents the 1st, 2nd and 3rd quartile distribution of the zenith opacity at 210 GHz.
A meteorological station was installed in May 2010, which was provided by researchers of the IAG (Instituto de Astronomía, Geofísica y Ciencias de la Atmósfera), Brasil, in order to monitor the main meteorological variables: temperature, humidity, atmospheric pressure, wind speed and wind direction, etc. These local variables are compared to those obtained in the Chajnantor region, Chile, where the ALMA interferometer is operating.
The Alto Chorrillo region has better infrastructure than the Macon zone. It may be accessed by driving along the RN51 (National Route, unpaved). It has high voltage lines and gas pipelines only 2 km away from the selected site. A railway is also a couple of kilometers away.
This place is also close to the town San Antonio de los Cobres (16 km in straight line), where one can find additional infrastructure (communications, fuel, hotels, school, hospital, etc.). This town, located 164 km westwards of Salta City, is the head of the Los Andes department and has a population of 6.126 people (2011 census).
It is worth mentioning that is under study the possibility to pave the RN40 along the trace that runs along the Salta
provinces. This route, running almost parallel to Los Andes
ridge, connects the northern province of Jujuy
with the southern extreme of Argentina (Santa Cruz
province), and is located only a few kilometers away from the selected site (Alto Chorrillos
) to install LLAMA. Furthermore, RN40 connects the LLAMA site with the RN52 to the north. The later links Argentina and Chile through Paso de Jama
, that is only 380 km away from the place where ALMA is located. In this way, once RN40 were paved, the distance between both Observatories (ALMA and LLAMA) could be covered by car in only 4-5 hours drive