The optical/infrared astronomical quality of high Atacama sites. I. Preliminary results of optical seeing

Giovanelli, R Darling, J Sarazin, M Yu, J Harvey, P Henderson, C Hoffman, W Keller, L Barry, D Cordes, J Eikenberry, S Gull, G Harrington, J Smith, JD Stacey, G Swain, M

R. Giovanelli et al., The optical/infrared astronomical quality of high Atacama sites. I. Preliminary results of optical seeing, PUB AST S P, 113(785), 2001, pp. 789-802

21

INGLESE

Article

Space Sciences

PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF THE PACIFIC

0004-6280 → ACNP

113

785

2001

789 - 802

ISI

0004-6280(200107)113:785<789:TOAQOH>2.0.ZU;2-F

The region surrounding the Llano de Chajnantor, a high-altitude plateau in the Atacama Desert in northern Chile, has caught the attention of the astro nomical community for its potential as an observatory site. Combining high elevation and extremely low atmospheric water content, the Llano has been c hosen as the future site of the Atacama Large Millimeter Array. We have ini tiated a campaign to investigate the astronomical potential of the region i n the optical/infrared. Here we report on an aspect of our campaign aimed a t establishing a seeing benchmark to be used as a reference for future acti vities in the region. After a brief description of the region and its clima te, we describe the results of an astronomical seeing campaign, carried out with a Differential Image Motion Monitor that operates at 0.5 mum waveleng th. The seeing at the Llano altitude of 5000 m, measured over 7 nights in 1 998 May, yielded a median FWHM of 1."1. However, the seeing decreased to 0. "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 repr esents the best seeing expected in the region; the set of measurements prov ides a reference base for simultaneous dual runs at Cerro Chico and at othe r 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 per centage of optically photometric nights in the Chajnantor region is about 6 0%, while that of nights useful for astronomical work is near 80%.