Črni Vrh Observatory

Telescopes

The 19-cm Automatic Comet Imaging Telescope

The Automatic Comet Imaging Telescope (ACIT) is an imaging device originally designed for Sky Survey Program and is run by University of Ljubljana and Crni Vrh Observatory. It utilizes a 19-cm, f/4 flat field S-C telescope and Wright Instruments CCD imaging detector, attached on the fully computerized mounting. A computerised BVRI filter wheel has been added to the system so that it is now used for CCD photometry of variable stars.

The whole system is being operated in Linux and may be run either in-site or remotely over the Internet link. An observing schedule, containing object coordinates, exposure time, filter and number of iterations is prepared for each night in advance and sent to the main computer. The image acquisition and processing is fully automated. Each night, many variable stars may be observed with any combination of filters.

The system consists of a fork-type friction driven mounting, the 19-cm, a f/4 flat field S-C telescope, a custom designed stepping motor controller, Wright CCD and 5- position filter wheel.

Information about our old ACIT configuration is also available.

CCD camera performance

CCD Sensor	EEV- CCD02-06-1-206, 540 x 380 pixels, 22 um x 22 um pixel size, back illuminated
Cooling	four stage Peltier at -76^oC
Dark current	0.06e^-/sec
ADU Conversion	gain 1 = 18.8e^-/ADU; gain 4 = 4.7e^-/ADU
Field of view	0.9^ox 0.6^o
Data format	FITS (14-bit)
Limiting magnitude	about 17^m in one minute exposure with V filter

Software

The TSERVER program takes care for the communication between hardware controllers for telescope, filter wheel, CCD camera and application programs. It controls the telescope and filter wheel positioning as well as image acquisition, while the image processing (Dark, Bias, Flat) is done by IRAF immediately after image acquisition. Each image header contains various data such as date-time of acquisition, duration of exposure, filters, WCS field coordinates and other information about the observation.

Operating strategy

The system is able to monitor single or a number of variable stars throughout the night with any combination of filters. Calibration images (dark, bias, flat) are taken automatically before and after each observing session. Images are processed in real time and analysed with IRAF software.

Telescope

Mechanics

The polar and equatorial disks are driven by 1:15 and 1:20 rollers, respectively, through 1:180 worm gears and stepper motors. Both motors are operating in micro stepping mode yielding microstep resolution of 0.11 arc seconds. The telescope slews across the sky at 0.9o/sec and has a pointing accuracy of 1-2 arc min over the entire sky.
The telescope mounting was designed by H. Mikuz, and D. Zgavec and built in a local workshop. Basically, the mounting is an improved copy of a 36-cm telescope which was designed by A. Cadez and B. Dintinjana.

Optics

Flat-field Schmidt-Cassegrain, 19-cm, f/4 with fully corrected flat field. The camera has a special bar cage structure, made of low-expansion Invar alloy that holds the mirrors at a permanent distance. This prevents shifting of the focal plane due to ambient temperature changes and enables to begin observations without losing time for focusing. Further details may be found in J. Brit. Astr. Ass., 100, p. 224-226.

Electronics

Stepping motor electronics is built around a 80535 microcontroller which provides signals for two pairs of LMD 18245 stepping motor drivers and inputs for stop switches and hand controller. It communicates with the central computer through a RS-232 port. During the operation it maintains its position for both axis and takes care for all the low-level signals.

The 36-cm AIT Imaging System

The 36-cm AIT System is an imaging device designed for wide range of observing applications and is run by University of Ljubljana. It utilizes a 36-cm, f/11 S-C telescope and Finger Lake Instruments, thinned CCD detector, attached on the fully computerized mounting. The system is being operated in Linux and may be run either in-site or remotely over the Internet link. An observing schedule, containing field coordinates, exposure time and number of scans is prepared for each night in advance and sent to the main computer. The image acquisition and processing are fully automated. We reach a limiting magnitude 18.5 in 1- minute exposure and about 20 in 5-min exposure with V filter. An additional telecompressor yields the f/6.7 ratio and is mainly used for searching purposes.

The system consists of a fork-type friction driven mounting, the 36-cm Schmidt-Cassegrain telescope, CCD camera and a custom designed stepping motor controller. Mechanics and electronics design are similar to ACIT system, described above.

CCD camera performance

CCD Sensor	TK 1024x1024 pixels, 24 um x 24 um pixel size, thinned, back illuminated
Quantum efficiency	80% @400nm; 93% @550nm; 89% @700nm; 49% @900nm
Cooling	two stage Peltier at -50^oC below ambient
Dark current	2.0 e^-/pixel/sec dark current @240K (-33^oC)
Read noise	16 e @ -30^oC
ADU Conversion	4.5e^- per ADU
Field of view	22 x 22 arcmin (at f/11); 37 x 37 arcmin (at f/6.7)
Data format	FITS (16-bit)
Limiting detection magnitude	about 18.5^m in one minute exposure without filter

Software

The TSERVER program takes care for the communication between hardware controllers for telescope, CCD camera and application programs. It controls the telescope and image acquisition, while the image processing (Dark, Bias, Flat) is done by IRAF ccdproc package in real time. Each image header contains various data such as date-time of acquisition, duration of exposure, WCS field coordinates and other information about the observation. The images are analyzed by the Fitsblink software. The program is able to do accurate astrometry of any moving object automatically by comparing the field stars with GSC, USNO-SA 2.0 and ACT catalogues. A MPC computer format report can be generated and sent to the Minor Planet Center

TSERVER program was written by Bojan Dintinjana. Fitsblink is a freeware program, written by Jure Skvarc.

Operating strategy

Each region of sky is covered three times on each night. As soon as the third scan is over, the software compares the lists of objects found by Fitsblink and check for the presence of any moving objects. Objects with known orbits are automatically identified and their astrometry is stored in a MPC format file. Finally, a list of image triples, containing candidate objects, is generated. The candidate objects are then visually checked.

Information about our old CCD configuration is also available.

Telescope

The 36-cm Schmidt-Cassegrain telescope

Finger Lake Instruments, 1k x 1k thinned CCD