System Description

TelescopeMeade LX200 12"
Sub aperture layoutTwo pairs diagonal
Sub aperture d7.4 cm
Sub aperture separation D20.5 cm
DetectorWATEC WAT-100N
Pixel scale0."667 (Horizontal) x 0."627 (Vertical)/pixel
Exposure time0.5, 0.2, 0.1ms adjusted to observing condition
CCD gain50 dB fixed
Wavelength0.5 um
Wavelength range0.3-1.1 um
Realtime data aquisitionLinux based PC
Sampling rate30 frames / second

Seeing values are calculated from image motions by the following procedures. An image motion is defined to be a variance of image centroids. The centroids are obtained in every captured frame and accumulated up to 60 data points to calculate the variance σ2. The relation between the Fried's seeing parameter r0 and the variance of the differential longitudinal image motion σ2 is given by

σ2l = 2λ2r0-5/3[ 0.179 D-1/3 - 0.0968 d-1/3]

Also the relation between r0 and the variance of the differential transverse image motion σ2t is given by

σ2t = 2λ2r0-5/3[ 0.179 D-1/3 - 0.145 d-1/3]

Here, λ is wavelength, D is a diameter of sub apertures and d is a distance between sub apertures. In case of our system, 0.5um for λ, 7.4cm for D and 20.5cm for d are adopted. FWHM θ is estimated numerically with λ and r0,

θ = 0.98 x λ/r0,

Finally, the zenith distance correction is applied,

θ(0) = θ(z) x cos(z)3/5,

where z is a zenith distance, θ(z) is the observed seeing and θ(0) is the seeing at zenith.