S. Ilyasov

Uzbekistan Academy of Sciences, Toshkent, Toshkent Shahri, Uzbekistan

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Publications (7)1.69 Total impact

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    ABSTRACT: We have determined the realistic seeing of the 1.5-m AZT-22 telescope of the Mt. Maidanak Observatory (Astronomical Institute, Uzbek Academy of Sciences) using more than 20 000 CCD frames with stellar images in the UBV RI bands acquired in 1996–2005: ε = 1.065″ in the V band. The characteristic seeing reduced to unit air mass, ε med V (M(z) = 1), is 0.945″. We derived color equations for the CCD detectors used with the telescope. Atmospheric-extinction coefficients in different photometric bands were also determined. The mean V -band atmospheric extinction is 0.20 m ± 0.04 m . The time needed for the conditions to settle, in the free atmosphere as well as inside the telescope dome, is 2–2.5 hours after the end of astronomical twilight. For nights with ε med V > 0.9″, we find a persistent difference between the seeing found at this telescope and measured simultaneously with a differential image motion monitor, amounting to ∼0.1 m .
    Astronomy Reports 01/2010; 54(11):1019-1031. · 0.76 Impact Factor
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    ABSTRACT: Results of 2005-2007 campaign of measurement of the optical turbulence vertical distribution above Mt. Maidanak are presented. Measurements are performed with the MASS (Multi-Aperture Scintillation Sensor) device which is widely used in similar studies during last years at several observatories across the world. The data analysis shows that median seeing in free atmosphere (at altitudes above 0.5km) is 0.46 arcsec and median isoplanatic angle is 2.47 arcsec. Given a rather long atmospheric coherence time (about 7 ms when the seeing is good) such conditions are favorable for adaptive optics and interferometry in the visible and near-IR. Comment: Accepted for publication in Astronomy Letters, V.35 (2009); 14 pages, 8 figures
    05/2009;
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    S. Ilyasov
    01/2002; 266:376.
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    ABSTRACT: The atmospheric turbulence and meteorology of the Maidanak Observatory in Uzbekistan are reviewed. Night time seeing was measured during the period August 1996 - November 1999 with the ESO Differential Image Motion Monitor. The median zenith seeing (FWHM) for the entire period of observations is 0.69” at 0.5 $\mu$m. A maximum clear sky season for Maidanak is July - September, with about 90% of possible clear time and a median seeing of 0.69$\arcsec$. The best monthly median seeing, 0.62$\arcsec$, is observed in November. The winter maximum of clear time is usually observed in February (up to 50%) with a FWHM of 0.77$\arcsec$. During an additional site testing campaign (9 nights) organized in July 1998, the median wavefront outer scale ${\cal{L}}_0$ of 25.9 m and a median isoplanatic angle $\theta_0$ of 2.48$\arcsec$ were measured with the Generalized Seeing Monitor developed at the University of Nice. The temporal evolution of the wavefront can be described by several layers moving at slow velocities with predominant direction from the West. This corresponds to a remarkably large atmospheric time constant. No correlation between wavefront velocity and the wind velocity at ground level was found. The good seeing, large isoplanatic angle and, especially, slow wind, place Maidanak Observatory among the best international astronomical sites for high angular resolution observations by interferometry and adaptive optics.

    Astronomy and Astrophysics Supplement Series 07/2001;
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    ABSTRACT: The night-time seeing measurements obtained with the ESO Differential Image Motion Monitor at Mt. Maidanak from August 1996, up to June 1999 are presented. This instrument was also used for seeing estimation at La Silla and Paranal Observatories in Chile in 1988 - 1996. The median value of seeing--(beta) FWHM (the full width at half maximum of a long-exposure stellar image at zenith at (lambda) equals 500 nm) for the entire period of observations is 0.69 arcsec. For the La Silla and Paranal Observatories, this parameter is 0.87 and 0.66 arcsec, respectively.
    Proc SPIE 11/1999;
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    ABSTRACT: Various parameters of the atmospheric turbulence above the Maidanak observatory located in Uzbekistan Republik were measured on 9 nights in July 1998 with three complementary instruments: Differential Image Motion Monitor (DIMM), Generalized Seeing Monitor (GSM) and two Scintillation Photometers (SP). Median FWHM seeing was equal to 0:64 00 , the median wavefront outer scale L 0 = 25:9 m, median isoplanatic angle ` 0 = 2:48 00 . Temporal evolution of the wavefront can be described by several layers moving at slow velocities (mostly less than 2 m=s and never exceeding 10 m=s) with predominant direction from the West. There was no correlation between wavefront velocity and the wind velocity at ground level. Turbulence in the 3 Gamma 30 m surface layer was not important, contributing on the average 10% to the total C 2 n integral (except on one occasion when it was very strong and dominant). Independent measurements of the free-atmosphere seeing (excluding the first kilometer above...
    02/1999;
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    ABSTRACT: We present the results of our 2005–2007 campaign to measure the vertical distribution of optical turbulence above Mount Maidanak. The measurements were performed with the MASS instrument, a multi-aperture scintillation sensor that has been widely used for such studies in recent years at many observatories worldwide. Analysis of the data shows that the median seeing in the free atmosphere (at an altitude of 0.5 km and higher) is 0 ″46, while the isoplanatic angle is 2″.47. Given the large time constant (about 7 ms at good seeing), such conditions are favorable for using adaptive optics and interferometric measurements in the visible and near-infrared spectral ranges.
    Astronomy Letters 35(8):547-554. · 0.93 Impact Factor