RTT150, main page
RTT150
Russian-Turkish 1.5-m Telescope


 
High energy Astrophysics department of IKI, Moscow
International astrophysical observatory Spectrum-X-Gamma
International astrophysical space observatory INTEGRAL

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HEAD IKI

Telescope's focal detectors

Until 2002 observations were mostly performed with ST-8E CCD in the 1:7.7 Cassegrain focus. It is equipped with a set of standard UBVRI filters and system of adaptive optics. Since the summer of 2002 AP-47p became the main detector, and ST-8E is used as a guiding CCD starting from September, 2002. In April, 2003 telescope was equipped with a larger-size CCD Andor DW436.


Andor CCD 

Andor DW436 with a filter wheel

Testing of Andor DW436 CCD as a focal detector of RTT150 telescope has started in Spring 2003. CCD has replaced AP-47p inside the assembly with ST-8E serving as autoguide (see photo). During the May 21-29, 2003 observing run in the autoguiding mode Andor DW436 CCD being cooled downto -60o has shown a very low noise level and extremely high image quality (see image).
 

Andor DW436 CCD characteristics
Chip Andor DW436
Size of active area 2048 x 2048 pixels,
27.6 x 27.6 mm
Total number of pixels 4,194,304
Pixel size 13.5 x 13.5 mkm
Dark current 1.7 e-/pix/hr
Readout noise 3.5e- rms @31kHz


AP47p CCD 

Since summer of 2002 the main focal detector of the RTT150 telescope was AP47p CCD in 1:7.7 Cassegrain focus. It is electrically cooled downto -45o -50o relative to the environment temperature.
 

AP47p CCD characteristics
Chip Marconi CCD47-10
Size of active area 1024 x 1024 pixels,
13.3 x 13.3 mm
Total number of pixels 1,048,576
Pixel size 13 x 13 mkm
Readout noise <10e- RMS
Frame readout time 20 s
Binning modes from 1 x 1 to 8 x 63
Exposures from 0.03 to 10400 sec, resolution 10 ms
Focus outlet 2.9 cm

During September 3-13, 2002 works on installation of new autoguiding system (photo 1) were carried out on RTT150 telescope. IKI and KSU specialists have taken part in this work. Installation of CCDs to the autoguide frame, frame assembly and its installation on the base bearing of a telescope was done. Adjustment of mutual position of the CCDs was made and preliminary adjustment of hardware-software parameters of autoguiding system was executed. The first test image of an area of the star sky with working system was received (image 1). 

The autoguiding system includes two electrically cooled CCD matrices. In Autumn 2002 the main matrix was AP47p by Apogee Instruments with CFW-8 system of filters (photo 2), the guiding one having been the ST-8E matrix from Santa Barbara Imaging Group (photo 3). Both matrices are assembled in one casing (photo 4, photo 5). AP47p is placed at the optical axis of a telescope and ST-8E is located at a right angle to the optical axis. The image gets to this matrix with the help of an additional flat diagonal mirror. Both matrices are connected to a computer with MaxIm DL/CCD software by Diffraction Limited company (http://www.cyanogen.com/products/maximdlccd) that controls the work of CCDs. The same program is used for issuing the control signals to fine correction drives of a telescope.


ST-8E CCD 

ST-8 on RTT150 ST-8E CCD by SBIG has a full resolution of 1530x1020 pixels and active area size of 13.8x9.2mm2. Corresponding field of view is 4.1' x 2.7'.

CCD is front-illuminated and has quantum efficiency of 30-60%. It is electrically cooled downto -35o from environment temperature. For this reason the CCD has quite a high dark current. Its value strongly depends on the CCD temperature and hense on the surrounding temperature. That's why correct calibration of the dark current is critical. 

CCD is equipped with a standard set of Johnson-Cousins UBVRI filters as well as SBIG AO-7 adaptive optics system.

ST-8E CCD characteristics
Chip Kodak KAF-1602E 
+ TI TC-211
Size of active area 1530 x 1020 pixels,
13.8 x 9.2 mm
Total number of pixels 1,500,000
Pixel size 9 x 9 mkm
Shutter Electromechanical
Exposures from 0.11 to 3600 sec, resolution 10 ms
A/D conversion 16 bit
A/D gain 2.3e-/ADU
Readout noise 15e- RMS
Binning modes 1 x 1, 2 x 2, 3 x 3
Pixels digitizing rate 30 kHz
Frame readout time 60 s
Focus outlet 2.3 cm

Filters

CCD is used together with CFW-8 filter wheel which has 5 cells. Five UBVRI filters corresponding to Johnson-Morgan system of photometric standards are used:
 
 

Color
U
B
V
R
I
Band, nm
340-380
390-490
510-590
595-805
770-990

CFW-8 system contains 5 standard windows of 1.25" diameter for threaded filters. The system is screwed at the rare side to the detector using metric adaptor.