Modern astrometric projects require precise positional measurements of objects down to magnitude 20m–22m. For ground-based observations, this is possible by the use of astrographs with apertures 1 meter or more with precise tracking using long exposures and precise timing. The multifunctional astronomical complex RTT150 (the 1.5-m Russian–Turkish Telescope) is appropriate for such purposes

Aslan, Z.

Gumerov, R.I.

Hudkova, L.A.

Ibragimov, A.A.

Ivantsov, A.V.

Khamitov, I.M.

Nemtinov, A.

Pinigin, G.I.

Shulga, A.V.

Kinematika i fizika nebesnyh tel (Online)

Наукова електронна бібліотека періодичних видань НАН України (Vernadsky National Library of Ukraine)

ASTROMETRY AT THE RTT150 TELESCOPEWITHIN THE INTERNATIONAL COLLABORATIONBETWEEN KSU (RUSSIA), TUG (TURKEY), AND NAO (UKRAINE)Z. Aslan1, I. M. Khamitov1, R. I. Gumerov2, A. A. Ibragimov2, A. Nemtinov2,A. V. Ivantsov3, L. A. Hudkova3, G. I. Pinigin3, A. V. Shulga31TUBITAK National ObservatoryAkdeniz Universitesi Yerleskesi, 07058 Antalya, Turkeye-mail: aslan@tug.tug.tubitak.gov.tr2Astronomical Observatory, Kazan State University18 Kremlyovskaya Str., 420008 Kazan, Russian Federatione-mail: rgumerov@ksu.ru3Research Institute “Nikolaev Astronomical Observatory”, MES of Ukraine1 Observatorna Str., 54030 Mykolaiv, Ukrainee-mail: pinigin@mao.nikolaev.uaModern astrometric projects require precise positional measurements of objects down to mag-nitude 20m–22m. For ground-based observations, this is possible by the use of astrographs withapertures 1 meter or more with precise tracking using long exposures and precise timing. The multi-functional astronomical complex RTT150 (the 1.5-m Russian–Turkish Telescope) is appropriate forsuch purposes.THE RUSSIAN–TURKISH TELESCOPE RTT150The 1.5-m telescope RTT150 was manufactured by the well-known optical-mechanical company LOMO(St.-Petersburg) and was moved after 1995 to Turkey [1, 6, 11]. In 1998 the work on the telescope’s as-sembly and installation in Antalya has been completed and a Joint Facility of the Kazan State University(KSU), the Space Research Institute of the Russian Academy of Sciences (SRI RAS), and the Turkish NationalObservatory (TUG) was ready to provide for scientiﬁc research.The optical scheme of the RTT150 telescope has a set of four optical systems (F/3, F/8, F/16 for the Casseg-rain focus and F/48 for the Coude focus). In addition, the telescope is equipped with two guides – Ritchey–Chretien telescopes – with 360 mm diameter mirrors, which can be used independently. The full FOV ofthe Ritchey–Chretien F/8 variant with the corrector installation is 88 arcminutes (300 mm). For the small ﬁeld(8′×8′) limited by the CCD size, the corrector is not necessary.RTT150 is equipped with three CCD cameras, which give a possibility to perform observations in stare modeand in drift scan one.The main camera is the ANDOR CCD (2K×2K, a pixel size is 13.5×13.5 mkm, CCD scale is 0.23′′/pixel).With this CCD camera, it has been possible to obtain images of the magnitude 22m stars with 10 minuteexposures; objects down to magnitude 20m with 5 minute exposures are registered with a good signal/noiseratio.The other two cameras, ST-8 and AP-47 (APOGEE), are the auxiliary ones of lesser sizes and lower sensi-tivities. ST-8, which is completed with an AO7 device, has so far been used as a photo guider. We note that,with this device, it was possible to record images with FWHM of 0.7–0.9 arcseconds in short exposures (upto 10 min). AP-47 will soon replace ST-8 as a guider and ST-8 can be attached to one of the 360 mm guidetelescopes.For longer exposure times, the new digital CCD camera DinaCam with a liquid nitrogen cooling could beused. This camera was developed at the Special Astrophysical Observatory. In addition to its extremely lownoise, the camera provides several modes of charge storage: stare mode, drift scan, forward-backward and theircombination. The DinaCam CCD camera is equipped with the ISD017AP CCD.c© Z. Aslan, I. M. Khamitov, R. I. Gumerov, A. A. Ibragimov, A. Nemtinov, A. V. Ivantsov, L. A. Hudkova, G. I. Pinigin,A. V. Shulga, 2004523The precise automatic drive mode of the telescope along a predicted trajectory is used to take images offaint objects in long exposures with the aim to decrease distortions of images of asteroids. A possibility forprecise tracking is recognized for telescope motion along the predicted trajectory, which is successfully used tocorrect irregularities of the general gear and to compensate the inﬂuence of diﬀerential refraction at great zenithdistances.The telescope is equipped with the computer control system developed at the KSU and SRI RAS that allowsone to perform observations:– in batch mode, when the list of objects (coordinates, moments of the start of an exposure, and exposuretimes) is prepared in advance and loaded into the computer control for pointing the telescope on the nexttarget;– via the remote terminal (PC), connected to the control PC, and (using the Internet) via local network.The computer control software has a user-friendly interface which allows one to control the telescope bothin interactive and automatic modes for performing observations in accordance with the prepared list of objects.OBSERVATION PROGRAMSThe main task of the RTT150 telescope is the astrophysical research: observations of distant objects (quasars,galaxies and clusters of galaxies, micro-lensing objects, etc.), the nearby galaxies and the Milky Way objects.However, the RTT150 with its equipment for a high quality imaging allow one to use the telescope for modernastrometry. Observations of extra galactic radio sources (ERS) and stars around them have been successfullymade within an international campaign for the reﬁnement of the connection between optical and radio coordinatesystems (2000–2003). Some observations have been also carried out for selected minor objects of the Solar System(2002–2003) with the aim to determine their positions.At present, a list of the observation programs and methods is prepared for new astrometric projects. In par-ticular, several problems concerning the research of the Solar System small bodies down to magnitude 20m arestarted, such as– determination and improvement of orbital elements of near-Earth asteroids (NEAs),– determination of masses of selected asteroids by taking into account their gravitational perturbations onorbits of the less massive asteroids,– participation in gathering precise positions of selected minor planets for ground-based support of the in-ternational program “GAIA Follow-Up”, and photometric observations of brief occultations of stars byasteroids.A FOLLOW-UP PROGRAMME FOR THE SPACE ASTROMETRY PROJECT GAIAThis program relates only to the astrometric aspect of the GAIA project for the Solar System object [9, 10].GAIA will provide many position measurements of objects of the Solar System with the unique precision. Aboutone million small objects in our Solar System, mainly asteroids, will be observed down to magnitude 20m.The highest precision, about 10 micro arcseconds, will be reached for stellar objects with magnitude brighterthan 15m. It will be about 200μ as for those of magnitude 20m. This precision will, however, be degraded forthe non-stellar and fast-moving objects, such as NEAs. It could then be about several mas. GAIA will performa wide scan of the sky and will have not generally the possibility of immediately re-observing an object justdetected. The faint and eventually fast objects are then likely to be lost.Therefore, observations on alert seems to be necessary in order to catch more data on these targets and follow-up from the ground. A follow-up program will be necessary to ensure these objects are not lost and to improvetheir ephemerides. Several means make it possible to organize these observations, in particular, disseminationof alarms by the Internet via mailing lists (Minor Planet Mailing List for example) or maintenance of the oﬃcialpage of targets. Within the Solar System Working Group of GAIA, the plans are to constitute a network forground-based observations in order to follow-up GAIA observations with the principal aim of conﬁrming newtarget detections by GAIA and to carry out any astrometric measurements necessary for the improvement ofthe orbital elements and the cataloguing of these objects.Once a network has been organized, it will then be possible, during the years before GAIA launch in about2010, to test the astrometric performances on representative targets, to set up operations of data recovery, todevelop and check a procedure for astrometric reductions, and then to prepare some experiments on full-scalealarms. Particularly, it will provide many positional measurements of the Solar System objects; also numerous524new objects will be detected. Some constraints imposed by the objectives of the GAIA follow-up network areavailable in [Thuillot W., Stavinschi M., private communication].For the proposed network, small telescopes down to 1.5-m seem to be well suitable for follow-up task. Fastmoving objects such as NEAs will require fast reactions in order to operate several telescopes after receivingan alert from the GAIA control centre. Ground based robotic or automatic telescopes would obviously be muchmore eﬃcient in order to shorten the reaction time. Besides, small telescopes are able to work in appropriatelocations. At present, there are already identiﬁed more than 10 telescopes which are interested in this program.In the near future, this network will be extended and a process established to make it eﬃcient for a follow-up:identiﬁcation of each limiting magnitude, determination of the individual astrometric accuracy, rules to apply fora fast reaction on alert. Also, CCD cameras on these telescopes are generally well suited for precise astrometryof fast and eventually faint objects. The telescope RTT150 could also be used for monitoring the objects downto 20m.CURRENT PROGRAMMES FOR COLLABORATING TELESCOPESWithin the joint project on the basis of international collaboration of KSU (Russia), TUG (Turkey) and NikolaevAstronomical Observatory – NAO (Ukraine), it is planned to perform positional and photometric observations ofthe Solar System small bodies in connection with GAIA project [2]. A fundamental problem for determinationand improvement of the orbits and also for studying the multiplicity and masses of the selected asteroidsdown to magnitude 20m is picked out within the project framework on the base of precise observations atthe 1.5-m telescope RTT150.In addition, observations of the brighter objects (down to 18m) will be carried out with the CCD telescopes ofNAO such as AMC (D = 190 mm, F = 2480 mm, CCD scale is 1.33′′/pixel), MCT (D = 160 mm, F = 2046 mm,CCD scale is 1.61′′/pixel), FRT (D = 300 mm, F = 1500 mm, CCD scale is 2.19′′/pixel). In 2001–2003,the telescopes AMC, MCT, FRT of NAO were modernized and equipped with perfect Universal CCD cameras(UCC) and necessary software for observations to implement the whole range of possibilities for high-accuracyobservations of stars and asteroids.The joint use of telescopes with diﬀerent limiting magnitudes and diﬀerent CCD ﬁelds of view will allowposition measurements of the Solar System’s faintest star-like or slow moving bodies with the highest precisionin small ﬁelds (8′×8′ for RTT150), and fast-moving objects with high precision in wide ﬁelds (about 30′×30′for NAO telescopes).During the period of implementation of the project (within the next 5 years) at the collaborating telescopes,there will be observed– about 80 asteroids down to magnitude 20m, which will be NEAs at distances less than 0.1 AU, allowingthe determination and improvement of their orbital elements,– about 100 asteroids with encounters, allowing the inclusion of task of mass determination in a programbefore GAIA.First observations of objects from the prepared list have begun in May 2004 at the RTT150. From 82 ob-servations of three minor planets and one NEA during one night, the mean error of a single observation wasevaluated using (O–C) values, to be in the range 0.02′′÷0.04′′ in both coordinates. Also, mean errors in the range0.01m÷ 0.08m for a single observation were obtained using V (O–C) values. An accuracy obtained shows a highpotential for such observations at the RTT150. In general, by using reference catalogues which have a highaccuracy and density (TC2, UCAC, USNO-B1, etc.) the expected positional accuracy of the Solar System smallbodies down to magnitude 20m, including fast and non-stellar asteroids in the near-Earth space, will be about0.02′′ ÷ 0.1′′.The use of contemporary ephemerides and TV CCD cameras for observations of occultation of stars byasteroids provides a new possibility to study dynamical and physical characteristics of the Solar System bo-dies. Such observations will not only allow to improve the accuracy of observed quantities, but will also givean opportunity to study the physical properties of the surfaces, to determine diameters, to study resolvableobjects, etc.Determination of an enough precise orbit of a single asteroid (in the case of NEA – its trajectory) is wellknown and approved. In the case of a binary asteroid, the problem is much complicated, because the rotation ofthe components would aﬀect the visible motion of separate parts of the binary asteroid. That’s why it is plannedto pay some attention for detection of possible satellites of asteroids (detection of binarity). Here we intendto combine exposures of the direct imaging with observations of occultation of stars by asteroids and carefulphotometric monitoring of the assumed resolvable binaries. For improving the ephemerides, it is planned to usefast photometry of the occultations besides astrometric methods. For this purpose, RTT150 will be equippedwith a fast photometer for observation of occultations.525One of the important characteristics of asteroids is their masses. It is planed to evaluate masses of someasteroids using the dynamical method, based on the analysis of perturbations of small asteroids by big ones.It is considered that such a method gives the smallest relative error. As shown by A. Fienga et al. [5] GAIAwill allow more than 100 asteroid masses to be determined accurately.METHODSIt is planned to use the method and experience of CCD observations that have been gained during the observa-tional program of extragalactic radio sources (stare mode). It is possible for asteroid observations in drift scanmode to use the covered strips method [6, 7] and the combined CCD method [4, 8].The covered strips methodThe ﬁrst and basic objective of the method is to get a direct image of asteroids with reference stars. Withthe availability of a reference catalogue of an enough density and accuracy (TC2, UCAC, USNO-B1), the taskto calculate object coordinates with the RTT150 observations can be fulﬁlled successfully.However, there can be lacks of reference stars in some ﬁelds of celestial sphere. In this case, the auxiliary ob-servations at the precise meridian circle AMC NAO can be used to get additional reference stars. For the methodof covered strips, a CCD detector is used in drift scan mode. The method is eﬀective for observations of the SolarSystem small bodies down to magnitude 20m by performing multiple CCD observations at the RTT150 andother telescopes within the project. Thereby, the observations of asteroids at the RTT150 are combined withthe AMC observations and the data are obtained in strip-scans of an enough length with the aim to includereference stars from precise catalogues, besides asteroids [6, 7]. The use of this method for our observations in2002–2003 has given positive results.The combined CCD methodThe use of CCD cameras in two modes (stare and drift-scan) is planned for diﬀerent optical channels ofthe RTT150 by applying the combined CCD method [4, 8].The combined CCD method of observations of NEAs or other small bodies is a new approach by usingtechniques and methods to study characteristics of a motion, which can provide a high positional accuracy.The principle of observation at the telescope with equatorial mounting, equipped with a multipurpose CCDcamera is in the base of this method. The CCD camera has the possibility to record celestial objects both instare and drift scan mode, i.e., small bodies are observed in stare mode with the ﬁxed telescope, and movingstar images are obtained in drift scan mode. So, we have stellar images both for small bodies and for referencestars with the moments of observations recorded with the aid of the time service. The combined method wassuccessfully used for observation of objects on geosynchronous Earth orbits [3].CONCLUSIONSTechnical parameters of the RTT150 and the ﬁrst observations of the selected asteroids have shown that it ispossible to determine high-precise coordinates of such objects, with an accuracy in the range of 20–40 mas,which satisﬁes the requirements of the GAIA Follow-UP Program.A network of the automatic telescopes, together with the narrow-ﬁeld CCD and wide-ﬁeld CCD, can beused for coordinated and precise observations of the Solar System bodies before GAIA is launched, or duringthe mission in alert mode.Acknowledgements. The authors highly appreciate the fruitful discussion with William Thuillot aboutthe GAIA mission and the follow-up programme.[1] Aslan Z., Bikmaev I. F., Vitrichenko E. A., et al. Preliminary Results of the Alignment and Hartmann Tests ofthe AZT-22 telescope // Astron. Lett.–2001.–27, N 6.–P. 398–403.[2] Aslan Z., Khamitov I. M., Gumerov R. I., et al. Astrometry at the RTT150 telescope within the internationalframework of KSU (Russia), TUG (Turkey) and NAO (Ukraine) // Research of Artiﬁcial and Natural NEOs andOther Solar System Bodies with CCD Ground-Based Telescopes: Proc. of Intern. Conf., May 17–20, 2004.–Mykolaiv:Atoll, 2004.–P. 16–17.[3] Basey A., Kovalchuk A., Kozyrev E., et al. Telescope Observations of Artiﬁcial Satellites of the Earth in the Re-search Institute NAO // Research of Artiﬁcial and Natural NEOs and Other Solar System Bodies with CCDGround-Based Telescopes: Proc. of Intern. Conf., May 17–20, 2004.–Mykolaiv: Atoll, 2004.–P. 18–19.526[4] Dedenok V., Abrosimov V., Pinigin G., et al. Study of near-Earth Artiﬁcial Objects by CCD Methods andDevices // Extension and Connection of Reference Frames using CCD Ground-Based Technique: Intern. Conf. /Ed. G. I. Pinigin.–Mykolaiv: Atoll, 2001.–P. 170–179.[5] Fienga A., Bange J. F., Bec-Borsenberger A., et al. Close encounters between asteroids before and during the GAIAmission // Astron. and Astrophys.–2003.–406.–P. 751.[6] Gumerov R. I., Kovalchyk A. V., Pinigin G. I., et al. // Kinematics and Physics of Celestial Bodies. Suppl.Ser.–1999, N 1.–P. 79–83.[7] Kovalchuk A., Pinigin G., Protsyuk Yu., et al. Extension of the Hipparcos Catalogue to the Faint Stars in the Se-lected Fields using the Nikolaev Telescope AMC // The Use of CCD Technique in Research of Solar System Bodies:Intern. Conf.–Mykolaiv: Atoll, 2000.–P. 52–60.[8] Kovalchuk A., Shulga A., Martynov M. Combined CCD Observational Method of Geostationary Satellite, Metho-dical and Technical Designs and Results // Extension and Connection of Reference Frames Using Ground-BasedCCD Technique: Intern. Conf. / Ed. G. I. Pinigin.–Mykolaiv: Atoll, 2001.–P. 194–200.[9] Mignard F. Observations of the Solar System Objects with GAIA. I. Detection of NEO // Astron. and Astrophys.–2002.–393.–P. 797.[10] Perriman M. A. C., et al. // Astron. and Astrophys.–2001.–369.–P. 339.[11] Vishnevsky G. I., Gumerov R. I., Pinigin G. I., et al. // Astron. and Astrophys. Transactions.–2003.–22.–P. 777–786.527

Astrometry at the RTT150 telescope within the international collaboration between KSU (Russia), TUG (Turkey), and NAO (Ukraine)

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Astrometry at the RTT150 telescope within the international collaboration between KSU (Russia), TUG (Turkey), and NAO (Ukraine)

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