First results of a site-testing programme at Mount Shatdzhatmaz during 2007-2009

We present the first results of site testing performed at Mt Shatdzhatmaz in the Northern Caucasus, where the new Sternberg Astronomical Institute 2.5-m telescope will be installed. An automatic site-monitor instrumentation and functionality are described, together with the methods of measurement of the basic astroclimate and weather parameters. The clear night-sky time derived on the basis of 2006-2009 data amounts to 1340 h per year. Principal attention is given to measurement of the optical-turbulence altitude distribution, which is the most important characteristic affecting the performance of optical telescopes. For the period from 2007 November-2009 October, more than 85 000 turbulence profiles were collected using the combined Multi Aperture Scintillation Sensor and Differential Image Motion Monitor (MASS/DIMM) instrument. The statistical properties of the turbulent atmosphere above the summit are derived and the median values for seeing beta(0) = 0.93 arcsec and free-atmosphere seeing beta(free) = 0.51 arcsec are determined. Together with the estimations of isoplanatic angle theta(0) = 2.07 arcsec and time constant tau(0) = 2.58 ms, these are the first representative results obtained for Russian sites, and are necessary for the development of modern astronomical observation techniques like adaptive optics.