Follow-up astrometry - how to secure NEO orbits

J. Ticha, M. Tichy, and M. Kocer
Klet' Observatory, Zatkovo nabrezi 4
CZ-370 01 Ceske Budejovice, Czech Republic


Near-Earth Objects (NEOs) are considered to be very interesting and remarkable members of the solar system. These small bodies - asteroids and comets - have the capability of making close approaches to or even collide with the Earth. The number of known Near-Earth Objects has increased enormously in recent years due to LINEAR and other large surveys (Spacewatch, LONEOS, NEAT and CSS). This discovery process has to continue by follow-up observations to obtain a sufficient number of precise astrometric data needed for an accurate orbit determination of newly discovered bodies along with a judgement of possible hazard for Earth. The follow-up process starts by confirmatory observations and continues over a sufficient observing arc in the discovery apparition. An accurate orbit determination requires observations from at least two oppositions. If an asteroid is not found in the next apparition, different from the discovery one, then it can be considered lost. This is particularly embarrassing for NEOs. Several professional observatories and a handful of amateur stations all over the world operating well equipped stations take part in NEO follow-up.

The Klet' Observatory has pursued NEO follow-up CCD astrometry since 1994. This follow-up programme covers confirmatory observations of newly discovered NEO candidates, continues over a sufficient observing arc of NEOs in the discovery apparition and also considers testing of newly discovered NEOs for possible cometary activity. A very important part of this programme are NEO recoveries in the second convenient apparition. A special attention is given to the Potentially Hazardous Asteroids (PHAs). The original Klet' NEO follow-up CCD astrometric programme has been pursued using 0.57-m telescope. The present magnitude limit of this programme has been about V=20 mag. The Klet' Observatory is one of the most productive world sites in this field.

An increasing magnitude limit of NEO surveys as well as a need for astrometric data for fainter objects (observations in a longer arc, recoveries, cases of "virtual impactors" etc.) shows that NEO observations need more observing time on larger telescopes. Considering both this urgent need of astrometric follow-up and our results and experience in minor planet and comet CCD astrometry done at Klet' since 1993, we have decided to bring into operation a new 1-m class facility working on a permanent basis - the KLENOT telescope.

The KLENOT project is a project of the Klet' Observatory, Czech Republic, devoted to astrometric observations of Near Earth objects, distant objects and comets. The KLENOT telescope is constructed using a 1.06-m primary mirror and a primary focus four lenses corrector to obtain a plane field of view 33 x 33 arcminutes. This telescope is equipped with a CCD camera Photometrics Series 300. A special software package has been developed for KLENOT at Klet' using a combination of programs running on Windows and Linux platforms. The system consists of observation planning tools, data-acquisition, camera control and data processing tools. Most of the software is associated with a SQL database.

The regular observing started in March 2002 (under the MPC code 246).

The main goals of the KLENOT project are confirmatory observations of newly discovered fainter NEOs, follow-up astrometry of poorly observed NEOs including so called Virtual Impactors, and recoveries of NEOs in the second convenient opposition, especially in magnitude range from 19.5 to 22 V. All CCD images are process not only for targeted objects, but also tested for possible new objects. The consequential scientific objectives of the KLENOT project are analysis of possible cometary activity of newly discovered bodies and follow-up astrometry of distant objects, i.e. Centaurs and brighter transneptunian objects.

The first results of the KLENOT project obtained during from 2002 March to 2002 September contain more than 1600 astrometric positions of NEOs. A larger part of these astrometric observations enabled both to confirm new NEO discoveries and to extend their observing arc. Astrometric data for 22 Virtual impactors were obtained by the KLENOT to help with removing impact solutions. We also obtained second nights for two faint Amor-type asteroid recoveries - 1998HG49 and 2000DJ8.

The first NEO discovery made by the KLENOT project is a detection of asteroid 2002 LK. This Apollo-type asteroid has a semimajor axis of 1.11 AU, eccentricity of 0.15 and inclination of 25.17 degrees. Having absolute magnitude H=24.2 it belong to small NEAs with an approximate diameter from 40 to 90 meters. It was discovered in the targeted field taken for follow-up astrometry of another Apollo-type asteroid 2002 JZ8 on 2002 June 1 as an FMO brighter than an original target but moving some 8 degrees per day at the time of discovery. This newly discovered NEA began the list of the KLENOT discoveries and extended the population of known Apollos. Although there are a lot of various follow-up stations all over the world and this object was put on the NEO Confirmation Page maintained by the Minor Planet Center promptly, only two observing stations at New Zealand and in Canada equipped with 1-m class telescopes were able to confirm an Apollo-orbit solution for this object in the time range of 24 hours after discovery. So it also shows the need for 1-m class or larger telescopes dedicated to follow-up.

Results obtained by the KLENOT team and telescope during the first half-year of its operation show that this facility dedicated for permanent follow-up astrometry can significantly help in tracking NEAs worldwide.

Oral presentation on IMPACT workshop Impacts: a Geological and Astronomical Perspective.

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