Site testing of the Sierra de Javalambre. First results

Abstract

We present the main characteristics of the proposed location for the Javalambre Astrophysical Observatory. The measurements have been obtained from spectrophotometric, photometric and seeing data obtained with different monitors and instruments on the site and publicly accessible meteorological satellite data. The night-sky optical spectrum observed in a moonless night shows very little contamination by the typical pollution lines. Their contribution to the sky-brightness is ~0.06 mag in B, ~0.09 mag in V and ~0.06 mag in R. In particular, the comparison of the strengths of the Sodium artificial and natural lines indicates that the site satisfies the IAU recommendations for a dark site. The zenith-corrected values of the moonless night-sky surface brightness are B = 22.8 mag arcsec^-2, V = 22.1 mag arcsec^-2, R = 21.5 mag arcsec^-2, I = 20.4 mag arcsec^-2, which indicates that the site is very dark. The extinction has been measured for the summer period, with a typical value of 0.22 mag in the V-Band, with the best measured value of 0.18 mag in a totally photometric night. The median value of the seeing in the V-band for the last two years (2008-9) is 0.71", with a mode of 0.58". The seeing values present a seasonal pattern, being smaller in summer (~0.69") than in winter time (0.77"). For 68% of the analyzed nights the seeing was better than 0.8" during the entire night. The seeing is found to be stable for rather long periods, in particular for the nights with good seeing values. The typical scale, for nights with the seeing below 0.8", is about 5 hours for variations within 20% of the reference value. The fraction of totally clear nights is ~53%, while the fraction of nights with at least a 30% of the night clear is ~74%.