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Atmospheric transparency in the optical and near IR range above the Shatdzhatmaz summit
O.Voziakova (Sternberg Astronomical Institute, Russia)

Atmospheric extinction in the MASS spectral band

Atmospheric transparency in near IR range

Example of a good photometric night. Red dots are instrumnetal magnitudes in Dchannel of MASS. Blue dots -- scintillation index

Transparency of the atmosphere in the near IR depends on the water vapor content. We estimate the amount of precipitable water using zenith wet delay of GPS-signal (Bevis, M. et al.,1994, Journal of Applied Meteorology, 33, 379). The GPS-data were obtained from a local GPS, installed by Sternberg Astronomical Institute in the frame of the geodynamics project. The meteodata were kindly provided by the Kislovodsk station of the A.M.Obukhov Institute of Atmospheric Physics (Russian Academy of Sciences).

To study atmospheric extinction based on the MASS-data, we use the classical photometric pairs method. Observational program has been extended by a special photometric list of non variable stars with similar colors. The measurements of these stars at equal and different air masses allow us to determine their magnitudes in the MASS spectral band (eff = 481 nm). Using these magnitudes, we study the night behavior of atmospheric extiction.
The list of photometric stars Name Bet_A Bet_T Eta_T Bet_T Gam_G Bet_U Del_L Bet_L Gam_U Eps_U Eta_U Zet_D Del_H Gam_L Zet_A Alp_C Alp_P RA(2000) 01 54 38 02 09 33 03 47 29 05 26 18 06 37 43 11 01 51 11 14 07 11 49 04 11 53 50 12 54 02 13 47 32 17 08 47 17 15 02 18 58 57 19 05 25 21 18 35 23 04 46 DEC(2000)mag(MASS)Spectr +20 48 29 2.72 A5V +34 59 14 3.08 A5III +24 06 18 2.84 B7IIIe +28 36 27 1.60 B7III +16 23 57 1.93 A0IV +56 22 57 2.34 A1V +20 31 25 2.61 A4V +14 34 19 2.18 A3V +53 41 41 2.42 A0Ve +55 57 35 1.75 A0pCr +49 18 48 1.78 B3V +65 42 53 3.12 B6III +24 50 21 3.16 A3IV +32 41 22 3.22 B9III +13 51 48 2.99 A0Vn +62 35 08 2.56 A7V +15 12 19 2.47 B9V

The seasonal behavior of precipitable water vapor. PWV shows clear seasonal variation, mainly due to seasonal course of temperature.Winter and Spring are the best seasons for infrared observations.

ri ri au au em Ma eo eo Ma Ma Ma ra er yr ql ep eg

Distribution Median = 9. 1-st quartile 3-d quartile

of precipitable water vapor. 1 mm = 6.1 mm = 13.9 mm

Some attempts to predict atmospheric conditions from groundbased meteorological data.

Distribution of atmospheric extinction in MASS Median = 0.23 mag 1-st quartile = 0.20 3-d quartile = 0.27 mag Vertical green line represents theoretical Rayleigh extinction for Shatdzhatmaz (0.16 mag).

To monitor the clear skies, we use the Boltwood cloud sensor, located at the Solar Station. Relationship between the sky temperature and atmospheric extinction in the MASS spectral band. Red line - median extinction in 2centigree bins.

The seasonal behavior of median atmospheric extiction. Minimum extinction is observed in winter, in the same period there are many clear nights.

Absolute humidity versus column of precipitable water vapor. Humidity data are provided by the Kislovodsk station of the A.M.Obukhov Instutute of Atmospheric Physics.