THE OBSERVATIONS OF THE NEAR–EARTH OBJECTS WITH THE ZA–320M PULKOVO TELESCOPE

Devyatkin A.V., Aleshkina E.Yu., Barshevich K.V., Baturina G.D., Bekhteva A.S., Gorshanov D.L., Krakosevich O.V., Kouprianov V.V., L’vov V.N., Smekhacheva R.I., Sochilina A.S., Tsekmejster S.D.

The Cassegrain ZA-320M Pulkovo telescope (D=32cm, F=320cm) is mainly used for observations of the Near-Earth Objects (NEOs are asteroids and comets), but also some other Solar system bodies, including geostationary objects (GEOs), constitute a considerable part of our observation program.

The scientific activities include the observations, their ephemeris support and processing (L’vov et al., 2002). Great attention is paid to the real nature of the objects and the methodology of their observations.

Now the ZA-320M is a fully automated telescope (Kanaev et al., 2002, Devyatkin et al., 2004). It operates in accordance with the pre-defined schedule by an optimal choice of the observation conditions for each object. There is also the possibility of the detailed remote control of, and the manual intervention into, the sequence of operations. All facilities including the imaging CCD camera, the pointing engine, the guidance (tracking), the filter wheel, and the dome are mechanized and can be remotely controlled. The precise time is maintained by the local Pulkovo time service.

Since April 2005 the ZA–320M telescope is equipped with the FLI IMG1001E CCD camera (1024x1024 of 24? pixels). As compared with the former SBIG ST–6 camera, the field of view (28' x 28') is increased by an order of magnitude. The camera has a lower readout noise, higher sensitivity, and faster readout (of less than 3 seconds). All these features help to do more accurate measurements with an increased number of reference stars, to observe fainter objects (now the limiting magnitude is equal to about 20^m.5 with a 5 minute exposure), and rapidly changing events.

The CCD frames are processed by the APEX and APEX-A software packages (Devyatkin et al., 2000, Devyatkin et al., 2004) that can determine the coordinates and magnitudes of objects. APEX-A can use various modern star catalogs (USNO–A2.0, USNO– B1.0, UCAC–2) with a choice of the objects’ approximation model and a method of reduction. The output data are presented in the standard MPC format.

The Table 1 illustrates some results of NEO observations. The column headers are as follows: Object, an object’s designation; N, a number of observations; (O - C)_αcos δ, the total mean value of (О–С) right ascension differences; σ_αcos δ, the mean error of a single RA. Observation; (O - C)_δ, the total mean value of (О–С) declination differences; σ_δ, the mean error of a single Decl. Observation; Δm, the object’s magnitude range.

Table 1. Some results of NEO observations at Pulkovo

Object	N	(O - C)αcos δ	σαcos δ	(O - C)δ	σδ	Δm
		"	"	"	"
9 Metis	46	+0.38	±0.18	+0.42	±0.24	8.6-10.9
433 Eros	65	+0.14	0.27	+0.43	0.28	11.4-12.6
1866 Sisyphus	24	0.00	0.24	+0.19	0.29	15.1-17.7
3122 Florence	18	–0.12	0.23	+0.19	0.25	15.9-17.7
3199 Nefertiti	27	+0.14	0.40	+0.18	0.35	15.5-17.9
3200 Phaethon	18	0.00	0.40	+0.03	0.37	16.3-18.4
4179 Toutatis	10	–0.17	0.42	+0.39	0.24	14.8-16.8
2004 FX31	22	+0.05	0.46	–0.02	0.50	17.3-18.9
2004 JA	33	–0.01	0.21	–0.09	0.17	15.6-16.8
2P/Encke	7	+0.33	0.51	+0.72	0.24	14.5-16.3

Some objects with variable brightness were also observed. For example, the asteroid 1999 HF1 appeared to be a quasi-variable object with a period near 20 minutes. The amplitude varies from date to date in the range of 0.1^m – 0.4^m. The total instrumental frequency band (~350–1000 nm) was used. The mean photometric accuracy of these observations is 0.06^m. Fig. 1 illustrates the brightness variation for this object within one of the observation series.

Fig. 1. The brightness variation of 1999 HF1 during 40 minutes of observations

The ephemeris support is based on the EPOS software package (L’vov et al., 2005). The EPOS package contains the database for about 300 thousand asteroids and 500 comets. Currently there are 3.5 thousand near–Earth asteroids (NEAs) in the database. The data are permanently updated using several well- known sources including the MPCs and Dr E. Bowell’s catalogs. It is possible to distribute the objects of various classes to different catalogs, to work with an user’s orbit elements for real and model objects, and to get selection in accordance with various conditions. The EPOS package provides an effective ephemeris support for observers. For example, it is possible to get a list of objects visible within the specified sky area at a pre-defined time-moment, or a list of objects observable in a specified place and night, or a current list of potentially hazardous objects, and of close approaches of asteroids to the major planets within the specified time-span. A high-precision ephemeris with many useful parameters may be computed for any object. The program also helps to estimate the observation accuracies, to reject observations with large errors, and to identify an object. Finally, the EPOS package can generate the impressive pictures of orbital motions of several objects in space and their apparent motions among the stars on the sky. Besides the incorporated data, the EPOS package can use various modern numerical ephemerides and star catalogs distributed on CDs.

Now the ephemeris support covers all NEOs accessible for observations at Pulkovo, including the objects discovered most recently. The observations at Pulkovo are not always feasible due to the weather conditions or rapidly varying brightness of NEOs. Nevertheless, the ZA–320M telescope shows a high level of readiness and productivity. This instrument is the leading one in NEA observations, being made in the CIS, and takes the 27^th place in the world rating as for May 1, 2005. This fact is illustrated by Table 2.

Table 2. NEODys Database Statistics of NEA Observations for May 1, 2005

Observatory Number of obs. Years 1 704 Lincoln Lab., NM 67969 1996-2005 2 046 Klet’ 14591 1970-2005 3 557 Ondrejov 13279 1993-2005 4 413 Siding Spring 13032 1973-2005 5 118 Modra 11310 1993-2005 6 151 Eschenberg Obs. 9851 1998-2005 7 246 Klet’ Obs./KLENOT 9752 2002-2005 8 699 Lowell Obs./LONEOS 5934 1999-2003 9 649 Powell Obs. 5275 1991-2003 10 691 Spacewatch 8099 1984-2005 11 H41 Petit Jean Mountain 7974 2003-2005 12 644 Palomar Mt./NEAT 6634 2001-2005 13 379 Hamamatsu–Yuto 6456 2001-2005 14 670 Camarillo 5887 1992-2005 15 658 NRC of Canada 5278 1991-2005 16 474 Mount John Obs. 5152 1971-2005 17 608 Haleakala–AMOS 5104 1994-2005 18 711 Mc.Donald Obs. 5092 1991-2005 19 703 Catalina Sky Survey 4785 1998-2005 20 360 Kuma Kogen 4736 1992-2005

Observatory Number of obs. Years 21 941 Obs.Pla d’Arguines 4576 2000-2005 22 610 Pianoro 4430 1995-2005 23 J95 Great Shefford 4178 2002-2005 24 587 Sormano 4126 1989-2005 25 291 LPL/Spacewatch II 4104 2001-2005 26 926 Tenagra II Obs. 4043 2000-2005 27 084 Pulkovo 3974 2001-2005 28 402 Dynic Astron. Obs. 3750 1990-2001 29 170 Obs. de Begues 3486 2000-2005 30 448 Desert Moon Obs. 3459 2001-2005      ... 85 A50 Andrushivka 905 2002-2005      ... 101 095 Crimea–Nauchnij 680 1967-2005      ... 125 121 Kharkov Obs. 463 1996-2001      ... 210 119 Abastumani 154 1968-1979      ... 244 94 Crimea–Simeis 100 1928-2004

During the years 2001-2005 more than 8000 observations of the Solar system bodies were made including more than 4000 observations of 450 NEAs and about 1000 observations of 21 comets. The observations were processed, the results being sent to the Minor Planet Center (see the MPC Circulars in the reference list). The mean accuracy of one observation varies in the range of 0.2'' through 0.4'' and depends mainly on the brightness and angular motion of an object.

Much attention is paid to investigation and improvement of the ZA–320 telescope automatic control system and of the observation methods for obtaining the high quality astrometric and photometric results.

In addition to the above mentioned follow–up activity, experimental observations of other types are in progress now. The first one is the astrometric monitoring of the close apparent approaches of asteroids to the stars, or to each other. It is high-accuracy astrometry with only one reference star or with no stars. The apparent angular distances between two or more objects are measured; this value being a function of orbital elements. The second one is related to the photometry by occultations of stars by asteroids. These two methods are tested. The first one is using the window with a decreased number of pixels of the CCD-matrix. This helps to reduce the readout-time to reasonable values. The second one is related to measurements of a broken star trace obtained by observing with the switched-off clock drive.

In spite of the most northern location and unstable weather, the Central (Pulkovo) Astronomical Observatory now proves to be one of the efficient world NEO follow–up centers. This activity will be more intensive (including the regular GEO observations) after reconstructing and putting into operation the MTM-500 telescope.

• Devyatkin A. V., Gritsuk A. N., Gorshanov D. L., Kornilov E. V. APEX – the software package for processing astronomical CCD observations // Izvestia GAO, 214, 2000, 455–468 (in Russian).
• Devyatkin A. V., Kanaev I. I., Kulish A. P., Rafal’sky V. B., Schumacher A. V., Koupriyanov V. V., Bekhteva A. S. Automation of astronomical observations on the ZA–320 mirror astrograph II. // Izvestia GAO, 217, 2004, 505–530 (in Russian).
• Kanaev I. I., Devyatkin A. V., Kulish A. P., Rafal’sky V. B., Vinogradov V. S., Koupriyanov V. V., Kornilov E. V. Automation of astronomical observations on the ZA–320 mirror astrograph // Izvestia GAO, 216, 2002, 128–156 (in Russian).
• L’vov V. N., Devyatkin A. V., Smekhacheva R. I., Tsekmejster S. D., Gorshanov D. L., Kornilov E. V., Koupriyanov V. V., Rafal’sky V. B, Sidorov M. Yu. Pulkovo program of NEO investigations // Izvestia GAO, 216, 2002, 218–222 (in Russian).
• L’vov V. N., Smekhacheva R. I., Tsekmejster S. D. http://neopage.nm.ru/eng/esupp/ main.htm
• Minor Planet Circulars M47449, M47506, M47994, M48317, M48619, M49222, M49389, M49426, M50321, M50564, M50596, M51155, M51329, M51469, M51499, M52494, etc.

Размещен 6 декабря 2006.