The Optical/Infrared Astronomical Quality of High Atacama Sites. I. Preliminary Results of Optical Seeing

Abstract

The region surrounding the Llano de Chajnantor, a high-altitude plateau in the Atacama Desert in northern Chile, has caught the attention of the astronomical community for its potential as an observatory site. Combining high elevation and extremely low atmospheric water content, the Llano has been chosen as the future site of the Atacama Large Millimeter Array. We have initiated a campaign to investigate the astronomical potential of the region in the optical/infrared. Here we report on an aspect of our campaign aimed at establishing a seeing benchmark to be used as a reference for future activities in the region. After a brief description of the region and its climate, we describe the results of an astronomical seeing campaign, carried out with a Differential Image Motion Monitor that operates at 0.5 mm wavelength. The seeing at the Llano altitude of 5000 m, measured over 7 nights in 1998 May, yielded a median FWHM of 1Љ .1. However, the seeing decreased to 0Љ .7 at a modest 100 m gain above the plateau (Cerro Chico), as measured over 38 nights spread between 1998 July and 2000 October. Neither of these represents the best seeing expected in the region; the set of measurements provides a reference base for simultaneous dual runs at Cerro Chico and at other sites of interest in the region, currently underway. A comparison between simultaneous measurements at Cerro Chico and Cerro Paranal indicates that the seeing at Cerro Chico is about 12% better than that at Paranal. The percentage of optically photometric nights in the Chajnantor region is about 60%, while that of nights useful for astronomical work is near 80%.

Worldwide site comparison for submillimetre astronomy

“…Furthermore, a scale height of the water vapour profiles on the Chajnantor area can be deduced from the quartiles of the plateau and the "Cerro". With the satellite measurements, we computed a 1/e scale height h e of the order of 1.1 km that is in a good agreement with measurements from Giovanelli et al (2001). The PWV quartiles at the South Pole were computed at saturation from radio-sounding balloons over a period of 40 years (see Chamberlin 2002).…”

“…Cerro Chajnantor and Chajnantor Plateau were extensively studied (see Giovanelli et al 2001) and the PWV quartiles between 2006 and 2010 can be found in Radford (2011). The values deduced from opacity measurements at 225 GHz are 0.61 mm (25%), 1.08 mm (50%), and 2.01 mm (75%) for the plateau; and 0.33 mm (25%), 0.61 mm (50%), and 1.36 mm (75%) for Cerro Chajnantor.…”

Application of distributed control techniques to the adaptive secondary mirror of Cornell's Large Atacama Telescope

“…The characteristic Greenwood Frequency is 2π/t 0 . The values for the atmospheric constant (τ 0 = 0.021s,V 0 = 15m · s −1 , and r 0 = 10cm) are taken from observations made at the Large Atacama Telescope site by Giovanelli et al 2,9 Substituting the values and using the previously defined shift operators we have, 47.831w(s 1 , s 2 , t) + 1.35104w(s 1 , s 2 , t) + . .…”

European Extremely Large Telescope: Cross-calibration of DIMM Monitors at Aklim Site

“…Núñez et al [4] was compared two DIMMs units during 14 nights at SPM (San Pedro Martir), the first DIMM is that used at the Observatorio Astronomico Nacional at SPM and the second DIMM is a NOAO RoboDIMM unit (RoD) is that of CTIO (Cerro Tololo Inter American Observatory). Giovanelli et al [5] was carried out an other comparison during two nights in 2000 October between ESO-DIMM-C1 and CTIO DIMM, The two devices were different in both hardware and software but the comparison between the data sets has shown a good agreement. Hach et al, [6] was carried out another cross calibrationin in July-August 2004 at Oukaimeden Observatory for DIMM and DIMMAR instruments( tow DIMMs developed in Oukaimeden Observatory).…”