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The atmospheric extinction is an important parameter for an astronomical site. The extinction directly affects
the observations reducing the available radiation, but the most relevant effect on the quality of the astronomical
data is the variation of the extinction across the sky and in the course of the observation at night. The aim is
to trace the atmospheric transparency at any astronomical site using MASS data.
The main goal of the present work is estimating the atmospheric extinction coefficient (mag/airmass) from
MASS database. Multi Aperture Scintillation Sensor called MASS is an instrument to measure the vertical
distribution of turbulence in terrestrial atmosphere by analyzing the scintillation of bright stars. Here we are
briefly reminding you of the principles of a MASS instrument and presenting also the detailed description of the
output data. In order to gain better understanding of the atmospheric photometry, we compute the atmospheric
extinction coefficient, its rms, and the associated information from MASS database using the evolution of flux
values of a star measured at ground level versus air mass which accounts for the flux loss. The technique used is
based on the Bouguer low. To treat the statistics data correctly and compute the correct extinction, one has
to know the filter. Correct value of the extinction is critical at most. For this reason, the atmospheric extinction
must be extracted only by good measurements. We then used the quality control of MASS data.
Also, in the current paper, we focus on the evaluation of nocturnal atmospheric extinction coefficient
(mag/airmass) and others statistics (time of acquisition, accumulation time, air mass, and HR number is used as
a star name only for information . . .) at Paranal observatory (70°24’05” W, 24°37’24” S, altitude 2635 m a.s.l,
in Chile.). In addition, the rms error of the coefficient has been calculated. It is absolutely needed to evaluate
the accuracy of each extinction measurement. For the first time, they were obtained from MASS database photo metric processing during 885 nights in the years 2004, 2005, 2006 and 2007. These results will almost lead to
complete its characterization. The project is implemented in the frame of the European Southern Observatory
contract No. PO 014190/HNEU.
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