The atmospheric extinction at the Complejo Astronómico El Leóncito and the Bosque Alegre station

The first and second order extinction coefficients in the UBVRI and DDO systems are derived for the first time at CASLEO. They define an extinction curve which is discussed on the basis of the atmospheric absorption theory. From this curve the first order extinction coefficients for the Washington and Stromgren systems are inferred. From the photometric point of view, CASLEO occupies a place of preference among the observatories of the world. A comparison of the UBV extinction coefficients obtained at Bosque Alegre with previous determinations supports the conclusion that the sky transparency at this station has deteriorated in the ultra violet in the last years. The complete version of this work will appear in Astrophys, & Space Sci.Asociación Argentina de Astronomí