Abstract
We have conducted a new campaign to measure the seeing at the site of the Observatorio Astronómico Nacional at San Pedro Mártir, this time with a DIMM instrument. The results obtained during 123 nights, over a period of almost three years, yield a median seeing of 0.60 arcsec and a first quartile of 0.48 arcsec. These measurements were made 8.3 m above the ground and with exposure times of 6 ms. We show that the seeing can be excellent and very stable for whole nights, with the best measurements yielding a median of 0.37 arcsec and a first quartile of 0.32 arcsec during more than eight hours of continuous observations. The current results are in very good agreement with our previous study of the site. The expected value of the median seeing 15 m above the ground and extrapolated to null integration time is 0.61 arcsec. Finally, San Pedro Mártir is compared with those major astronomical sites in the world where seeing has been measured with DIMM instruments. This comparison allow us to conclude that San Pedro Mártir is one of the best astronomical sites in the world.
