Contribution of the surface layer to the seeing at San Pedro Mártir: Si-mul-ta-neous microthermal and DIMM measurements

Abstract

Results from experiments measuring the contribution of the surface layer to the optical seeing at the Observatorio Astronómico Nacional at San Pedro Mártir (OAN-SPM) are reported. Microthermal sensors placed at 7 levels on a 15-m-high instrumented mast were used to measure the structure constant of the refractive index C[n]2. The integrated seeing parameter was measured with a Differential Image Motion Monitor during 23 nights. Log-normal statistics were found for the seeing with mean of 0.98 arcsec and median value 0.84 arcsec . The contribution of the surface layer (2.3 to 15 m) to the total optical turbulence has a mean value of 16%, which corresponds to a degradation of 10% of the total seeing. These values are similar to those found in other observatories around the world, suggesting that the presence of trees in the OAN-SPM does not have a significant effect on the surface layer seeing. Further studies should provide a confirmation of this tendency.