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1 Introduction

The Carlsberg Meridian Telescope (CMT) has recently undergone a major upgrade. A 2k by 2k CCD camera has been installed with a Sloan r' filter operating in a drift scan mode. With the new system, the effective exposure time is about 90 s, the magnitude limit is $r'_{\rm CMT}=17$ and the initial positional accuracy is in the range 0.05'' to 0.10''.

The main task of the CMT is to map the sky in the declination range -3 $\hbox{$^\circ$ }$ to +30 $\hbox{$^\circ$ }$ with the aim of providing an astrometric, and photometric, catalogue that can accurately transfer the Hipparcos/Tycho reference frame to Schmidt plates. A secondary survey is also planned that extends the declination range covered to -15 $\hbox{$^\circ$ }$ in the South and +50 $\hbox{$^\circ$ }$ in the North. Projects similar to the CMT (UCAC, Zacharias et al. 2000 and CMASF, Muiños et al. 1998), which include the Southern hemisphere, will also be able to provide astrometric calibration for VISTA and other deep wide-field surveys.

The two main systematic errors affecting the data are caused by image motions due to long timescale atmospheric turbulence and charge transfer efficiency (CTE) problems linked to the CCD. Methods are described on how to calibrate these errors.


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Up: The Carlsberg Meridian Telescope survey

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