Wavefront outer scale and seeing measurements at San Pedro Mártir Observatory

The first measurements of the spatial coherence outer scale at the Observatorio Astronómico Nacional at San Pedro Mártir (OAN-SPM) are reported along with long term seeing measurements. These parameters were measured with the Generalized Seeing Monitor and with a Differential Image Motion Monitor. An instrumented mast was also used to measure the structure constant of the refractive index $C_n^2$ in the first 15 m. Log–normal statistics were found for the seeing and for the outer scale, with median values of $0.92''$ and 27.0 m, respectively. The distribution of the outer scale values is similar to that found in other observatories around the world, suggesting that the presence of trees in the OAN-SPM do not affect the outer scale values. Correlation studies suggest that large values of the seeing and the outer scale are likely to occur when the wind blows from the SSW. Further studies are recommended to confirm this tendency.