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Astron. Astrophys. 320, 642-651 (1997)

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An optimized detection technique for faint moving objects on a star-rich background

A search for the nucleus of comet 46P/Wirtanen * **

H. Boehnhardt 1, J. Babion 1 and R.M. West 2

1 Institut für Astronomie und Astrophysik, Universitäts-Sternwarte, Universität München, Scheinerstr. 1, D-81679 München, Germany (hermann@vlt.usm.uni-muenchen.de for H. Boehnhardt) and (babion@usm.uni-muenchen.de for J. Babion)
2 European Southern Observatory, Karl-Schwarzschild-Str. 2, D-85748 Garching, Germany (rwest@eso.org)

Received 23 February 1996 / Accepted 26 June 1996

Abstract

A novel method is proposed for the efficient detection of faint solar system objects moving in front of a star-rich field. After the removal of the background objects by means of seeing template frames and accurate image alignment on the moving object, subsets of frames selected by different criteria (e.g. seeing) are co-added to improve the signal-to-noise ratio for the image of the object. Requirements for the successful application of this procedure are discussed and verification checks for identified candidates are outlined. The procedure provides accurate astrometric positions and approximate magnitudes for identified objects.

The method was applied to a search for the [FORMULA] -mag nucleus of comet 46P/Wirtanen, the prime target of ESA's ROSETTA mission, while at heliocentric distance 4.6 AU and located in a field near the direction to the Galactic Centre. A 24.2 mag candidate image was marginally detected in CCD frames totalling 176 min integration time and taken on June 26, 1995, with the 2.2-m telescope at ESO La Silla. However, because of insufficient, corroborating data from other nights (caused by adverse atmospheric conditions), an unambiguous confirmation of this detection is not possible. The corresponding upper limit of the radius (assuming albedo of 0.04) is only 0.8 km (the likely radius is 0.69 km), indicating that comet 46P/Wirtanen possesses one of the smallest cometary nuclei known so far.

Key words: comets: general; 46P/Wirtanen – methods: data analysis; observational

* based on observations obtained at ESO La Silla within ESO programme No. 55-F-0337
** the comet was finally recovered on 25 April 1996, see comments under Note Added in Proof

Send offprint requests to: H. Boehnhardt

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© European Southern Observatory (ESO) 1997

Online publication: June 30, 1998
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