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Pic du Midi Observatory Images of Comet Hale-Bopp


Observers: Francois Colas, Jean Lecacheux
Location: Pic du Midi Observatory, France
Date: March 31, 1997 20:50 UT

H2O+ images, March 31st

We used a 50mm photographic objective with a HiSiS-44 CCD camera based on the Kodak KAF-1600 chip. The field of view was 20 degrees. The goal was to observe the ion tail. It is difficult to detect this faint feature close to the coma because of the large amount of light reflected by dust. To realize this observation, we used a narrow band filter centered at 715 nm, where is an emission band of the ion H2O+. To measure the continuum light we use an I filter. This filter is not exactly a continuum filter, but ion emission lines do not exist in this spectral region . Image A is the sum of 5 exposures of 5 minutes, and image B is the sum of 5 exposures of 40 seconds. The ratio of exposure times was derived from calibrations under solar illumination , so C image is only the substraction of image A by image B. The dust and ion tails are clearly visible on image A, but on image B, only the dust tail is visible. Image C shows the ion tail close to the nucleus. It is merged in the bright coma center on most of the image seen on the Web. In particular, two streamers are visible in the coma.

Contact: Francois Colas (

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