Map and location

OVERVIEW OF THE AUTOMATIC TELESCOPE SYSTEM

The Perugia Automatic Imaging Telescope (AIT) has been inaugurated in 1994, and is one of the first robotic telescopes in the world. The telescope is mainly dedicated to the automatic optical variability monitoring of blazars and few cataclismic stars. AIT is a 0.40 m newtonian reflector (f/5) with an equatorial mount. For the slewing and traking in RA e DEC we used two brushless motors controlled by a two axis motor controller connected to PC386 (PC1) via a RS232 serial line.

The pointing accurancy (without centering) is better then 1'.5. For the automatic guide a CCD camera was applied at the 15-cm refractor telescope which is joined to the main telescope on the same mount. The camera is supported by a motorized XY stage and can explore about half square degree on the sky around the target object: enough to find a bright guide star in the 90% of exposures. The guide star is selected automatically from the SAO Catalog.

A PC486 (PC2) controls the CCD camera applied at the newtonian focus of the main telescope and equipped with BVRI filters. All the software was written in C. The system can operate with or without the presence of the observer. In unattended mode the system needs an objects list stored in a working file compiled with the help of an opportune program which asks the user for object coordinates, filters, exposure times etc.. During the night the file is analized by the control software and an ordered pointing sequence is generated taking into account of the best observational conditions for each object. After each pointing a guide star is found, PC1 starts the automatic guide of the telescope and send a command to PC2 which begin the exposure. At the end of the exposure the image is saved in the Hard Disk of PC2. This process continue until the last object in the list is observed.

Nevertheless the system can be operated directly by the astronomer by means of an interactive menu-driven software, running on PC1, with many utility and diagnostic routines and on-line access to some catalogues (Bright Stars, GCVS, Landolt's Stars, SAO's Catalogue). The photometric CCD camera can also be controlled by an interactive software, running on PC2, containing a modified version of DAOPHOT routines for automatic star finding and evaluations of the instrumental star magnitudes.

THE CCD PHOTOMETRIC SYSTEM AND ITS PERFORMANCES

The CCD camera used were purchased from Spectrasource Ins. Ltd. and are based on the Texas Instrument chip TC211 with 192x165 pixels, cooled by a Peltier stage that reduces the CCD temperature of 50 C respect to the ambient. The use of these small area CCD can be justified only by the extreme precision of the telescope pointing system so that the size of the array is not a serious limit.

They have a good quantum efficiency, are cheap, not bulky and are very uniform, so that the usual correction of the images by a flat field is not reccomended. Nevertheless their main limits are high dark signal and excessive readout noise.

The photometric camera is equipped with BVRI Johnson-Cousins filters. In the usual atmospheric conditions at our site we can do absolute photometry with a tipical standard deviation of 0.06 magnitudes while in differential photometry whe can reach 0.02 magnitudes. With this system we can study variability of objects brightest than 17 magnitudes on V.