Site Testing of the Sierra de Java']Javalambre: First Results

We present the main characteristics of the Pico del Buitre, at the Sierra de Javalambre, 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. We have also used publicly-accessible meteorological satellite data to determine the total time useful for observations. 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 similar to 0.06 mag in B, similar to 0.09 mag in V, and similar to 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 2 yr (2008-2009) is 0.71 '', with a mode of 0.58 ''. The seeing values present a seasonal pattern, being smaller in summer (similar to 0.69 '') than in winter (similar to 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 hr for variations within 20% of the reference value. The fraction of totally clear nights is similar to 53%, while the fraction of nights with at least 30% of the night clear is similar to 74%.