Russian version

AZT-8 70-cm Telescope



General Description

The two-mirror telescope AZT-8 was manufactured by the Leningrad Optical-Mechanical firm (LOMO) in 1964. The optical system of the telescope is Cassegrain. It has an 70 cm main parabolic mirror with F/4, two secondary mirrors that give Cassegrain foci F/16 and F/40 with good fields of 40 and 18 arcmin. The primary focus gives a good field near 10 arcmin.

         

Mounting: Equatorial
Main mirror: Paraboloid, D = 70 cm, F = 282 cm
Optical systems: Prime focus (F/4), Cassegrain (F/16, F/40)
Instrument: BVRI Photometer with Apogee AP7p CCD-camera

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History

Firstly the AZT-8 was installed in Simeiz in 1964. It was used for photoelectric photometry and polarimetry as well as for TV observations. Main goal of the observations was symbiotic and double stars (T.S.Belyakina, E.S.Brodskaya), T Tau-stars (P.P.Petrov), UV Cet-stars (P.F.Chugainov).

In 1977 AZT-8 was transferred to Nauchny and installed in a new large pavilion with a shifting roof. Here AZT-8 was used to test a multichannel spectrometer constructed by A.F.Lagutin, L.V.Granitsky, A.B.Bukach et al. at the CrAO as a ground model for a device on board of the space mission "Astron". Main elements of the construction were designed and some particularites of the scanning drive and technical data of device were considered.

As a by-product the rapid variations of the atmospheric extinction was investigated, and energy distribution of some C-type-stars was obtained.

In 1990-s the photometric equipment for wide-range stellar photometry was developed in the Crimean Astrophysical Observatory in collaboration with Astronomical Institute of St.Petersburg University. Two telescopes (AZT-8, 0.7 m, F/18 and AZT-7, 0.2 m, F/10) on the same mount were equipped, correspondingly, with JKLM-photometer and BVR-photometer. The system permits to obtain simultaneous energy distribution for various stars in the range 0.4-5.0 mcm. The multicolor photometry of some X-ray-sources was carried out by V.M.Larionov, and some results of the BVR-photometry of RV Tau-type-stars were obtained by V.I.Burnashev.

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Instruments and Detectors

The telescope was upgraded in the early 2000s (Sergeev et al. 2010). In 2001 the AP7p CCD camera has been installed in the prime focus of the AZT-8 to carry out BVRI photometric observations. The computer-controlled filter wheel for this camera was developed and manufactured at the Crimean Observatory. The CCD array has a size of 512×512 pixels, giving a field of view of 15'×15'. The camera has a set of B, V, R, R1, and I filters, where the filter designated R1 closely resembles the Cousins I filter, while the other filters closely resemble the standard Johnson filters (see Doroshenko et al. 2005 for more details). By December 2001, intensive photometric monitoring of Active Galactic Nuclei (AGNs), including quasars and BL Lac objects, has been started using this new photometer. The configuration and testing of the AP7p imaging system have been completed at the Ohio State University (OSU). The Quantex control computer was specially configured to operate the AP7p, and was assembled from spare parts at OSU. The computer-controlled pointing of the 70-cm telescope using optical encoders has been developed in 2002. All these equipment have been purchased under US Civilian Research and Development Foundation.

        

BVRI-photometer with the CCD camera AP7p. Numbers denote: 1 - Signal cable connector,
2 - «Ground» connector, 3 - Absorber to dry air inside the wheel of filters, 4 - Connector to control filter positions, and 5 - Stepper motor to rotate the wheel of filters.

Readnoise: 2.3 ADU = 13 e
Gain: 5.6 e/ ADU
QE: 85% Max
Geometry: 512×511 pixels, 24×24 microns
Field of view
(AZT-8 prime focus):
15×15 arcmin, 1.755 arcsec/pixel
Well Depth: 210,000 e
Dynamic resolution: 16 bits, 35 kHz
Cooling: 50-55C below ambient

Characteristics of the AP7p CCD camera.

Filter name Center (Å) Comment
B 4330 Johnson B
V 5480 Johnson V
R 6950 Johnson R
R1 8160 Cousins I
I 8510 Johnson I
Filter transparency curves.

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Observations

When the control computer is loaded, its time is synchronized with the Universal Time and the Telescope control program starts. The program allows the telescope to be pointed at a specified position. Various types of information useful for an observer can be displayed: the start and end times of observations, the times of sunrise, sunset, moonrise, and moonset at the current date, the elevation of the observed object above the horizon, etc. In addition, the time interval during which the chosen object is accessible to observation or the time left until it becomes accessible to observation is displayed. Also shown are current telescope coordinates α, δ, and a hour angle t.

Then the observer starts the program to control the process of observations. To set the object coordinates it is sufficient  to select the object name from the database. When the coordinates are entered, the telescope control program will automatically choose an optimal telescope path in such a way that the lower end of the tube will not hit the supporting pillar and the tube will not sink below a dangerous limit in elevation above the horizon. The automatic pointing accuracy is about 2 arcmin, so the observer points the telescope more accurately manually by using the remote control (see number 6 on the figure below).

After the pointing, the observer focuses the image and begins to expose the objects. It is possible to do either a single exposure or a sequence of exposures, both of them can be repeated a specified number of times. The standard sequence of exposures for AGNs consist of the B, V, R, R1, and I filters with exposure time to be 60, 40, 30, 25, and 40 s, respectively. These can be changed proportionally, depending on the object brightness. As a rule, for each object, the B, V, R, R1, and I sequence of exposures is repeated four times. Also exposed are the technical frames : bias, dark, and flat field. The flat field frames in each filter is usually obtained in the twilight sky at sunset or at sunrise.

We have more than 50% of the telescope observing time. This time is mainly scheduled for photometric monitoring of selected AGNs to support for spectral observations as well as for the concurrent observations in other bands (HST, RXTE, BeppoSax), and to study patterns of the continuum variability, in particular, to measure a lag between different continuum bands. The list of targets to monitor consists of 50  AGNs of both  Seyfert 1 and BL Lac types. Other observed objects are Super Novae, pre-main sequence stars, X-ray sources, GRB afterglow, and some other. Since December 2001, more than 320,000 CCD frames, including technical exposures, have been obtained, of which about 200,000 are AGN frames.

AZT-8 Observer place. Numbers denote: 1 - 220V to 110V power transformer, 2 - UPS, 3 - control computer,
4 - telescope control unit interface,  5 - computer monitor, and 6 - remote control for the thin telescope motion.

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Main Scientific Results

From our photometric light curves, it was found interband lags between variations in the B band and variations in the V, R, and I bands for a sample of 14 AGNs. The lag scales with luminosity as t=Lb, where b= 0.4-0.5 (Sergeev et al. 2005). These results were interpreted in terms of the reprocessing model in which optical emission is mainly reprocessed emission that arises in the accretion disk heated by an X-ray source above the disk.

In several more papers, the properties of the optical and X-ray variability of AGNs have been compared (Doroshenko et al. 2009, 2010; Chesnok, Sergeev, & Vavilova 2009).

The Crimean photometric data were used to construct a reprocessing model which is able to reproduce the observed optical light curve from the X-ray light curve in Mrk 79 and NGC 4051 ( Breedt et al. 2009, 2010). Our data were also used as a support for spectral observations in the reverberation mapping studies (e.g., Denney et al. 2010; Doroshenko et al. 2012; Sergeev et al. 2011).

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