Information from the European Southern Observatory

 ESO Press Photo 20/97

 22 July 1997                                                       

 For immediate release
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Lightcurves of Asteroid (3671) Dionysus

 [ESO Press Photo 20/97]  This figure shows the lightcurve data from
                          observations of asteroid (3671) Dionysus, made
                          from ESO on June 8th, 1997. These observations
confirm that this asteroid is accompanied by a small moon (natural
satellite).

In this diagramme, the abscissa indicates the time and the ordinate the
light intensity (brightness), expressed on the logarithmic magnitude scale.
The three curves have been shifted vertically by an arbitrary amount so as
not to overlap.

The upper curve shows the `normal', periodic light variation due to the 2.7
hour rotation of the irregularly shaped asteroid. This curve has been
derived by fourier analysis of photometric observations taken during the
period June 1-16.

The middle curve displays the observations taken on June 8th, revealing an
eclipse event.

The bottom curve represents the difference between the observed curve
(middle) and the average curve (upper). This procedure `removes' the light
variations caused by the rotation of the asteroid. The minimum caused by an
eclipse in the double asteroid system is now clearly seen. The similarity
with the lightcurve of a partial eclipse in a double stellar system is
striking.

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This is the caption to ESO PR Photo 20/97 [GIF, 10k] which accompanies ESO
Press Release 08/97 (22 July 1997). It may be reproduced, if credit is given
to the European Southern Observatory.

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                © ESO Education & Public Relations Department
           Karl-Schwarzschild-Strasse 2, D-85748 Garching, Germany
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