Abstract

Minor Planets Approaches to Stars:
CCD Observations

Ricard Rodriguez

Bei nahen Begegnungen von Kleinplaneten mit Sternen können durch CCD-Beobachtungen die engsten Distanzen und deren Zeitpunkte bestimmt werden. Dabei ist es möglich, jeweils eine halbe Stunde vor und nach der engsten Begegnung die Meßreihe zu unterbrechen, um eine eventuelle Bedeckung mit anderen Systemen zu beobachten.

Since 1993, amateur and professional astronomers from Spain have taken many CCD images of close approachs of minor planets to stars to determine their minimum distance and time.

This observing program began on reading a note in the EAON Circular about the visual determination of distance and position angle of asteroids with respect to a star. Knowing the possibilities of the software of STx CCD cameras, we worked with amateur astronomical associations on preparing instructions for observers and on the software to reduce the data.

With this program we obtain something more than just a positive or (most often) negative occultation observation. We introduce a whole new reason to observe these phenomena.

Since autumn 1997 these observations are a routine program (one hour per day for routine observations) in the 82cm IAC-80 telescope, operated on the island of Tenerife in the Spanish Observatorio del Teide of the Instituto de Astrofísica de Canarias.

Observation Program Outline

Between half an hour before and half an hour after the time of minimum distance, we obtain CCD images. It also is possible to break the series to observe, either visually or with another system, the possible occultation.

Previous reduction

Determine the time of mean exposure with a precision of 1 second. Determine the coordinates of the centroids of the minor planet and the star.

Final reduction

Determine the minimum distance by fitting a straight line to the path of the minor planet and determine the time of closest approach.

Fig 1. Selected CCD images of (451) Patientia approach to the star TYC 6844 01393, obtained on IAC-80 telescope operated on the island of Tenerife in the Spanish Observatorio del Teide of the Instituto de Astrofísica de Canarias.

Fig 2. Reduction graph showing the asteroid centroids and using the star as reference at the origin.

Ricard Casas Rodriguez, Instituto de Astrofísica de Canarias, Tenerife, Spain
Address: 38200 La Laguna (Tenerife), Spain E-Mail: rcr@ot.iac.es
Telephone: +34 922 605200 Fax: +34 922 605210

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