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Comet Hale-Bopp Arm FormationAnimation


August 30, 1995

This animation is courtesy of Miguel Serra-Ricart from Teide Observatory. The The images were taken by M.R. Kidger with the IAC80 Telescope (0.82m) pertaining to the Instituto de Astrofisica de Canarias in the Canary Islands, Spain.

Arm formation movie from the IAC80 Telescope. This animation shows a series of processed images from August 25th, 27th and 28th which show the development of the spiral arm leaving the nucleus. The seven images are the sum of between 6 and 8 exposures on each occasion: the first three covering 2.5 hours of monitoring in R on the 25th, the fourth covers 2.0 hours of monitoring in R, through cloud, on the 27th (and is thus of much lower quality), while the last three images cover 2.25 hours of monitoring in B on the 28th. A gaussian has been fitted to the coma and then subtracted to show the jet which is also clearly visible in the raw images. The sequence shows how the base of the jet remains in a constant position over the three nights and does not rotate around the nucleus. The jet though changes significantly from night to night, wrapping further around the nucleus, moving slowly away and fading significantly. Comparison of images in R and B on the 28th shows no major differences in the structure.

The revised arm formation animations from August 31st and September 6th contain images from further nights and a reprocessing of some of the earlier images, which has improved their quality. In the September 6th animation we include images from August 15th (no jet), 25th, 27th, 28th, 31st, September 4th, 5th, 6th (jet now very faint) and 7th (jet invisible). This fading of the jet is real and not due to the moon, because we could see the jet very clearly on the 4th, when Hale-Bopp was close to the moon, but not three nights later when the background was much lower. Unlike the early version of the animation, each image is the sum of a complete night of data (usually one and a half to two hours of total exposure). Individual exposures are usually 300s and are co-added to produce the final summed image.

One interesting aspect of the jet is the way that the initial straight section out of the nucleus grows in a very linear fashion from night to night. Extrapolating back, the jet would have had zero length on August 17th. This is not necessarily though genuinely the date that the feature appeared. By the 4th it had more than doubled in length to 11.2 arcseconds. We do appear to detect a small degree of precession of the jet in our images, but without being able to give a definite period yet; this might be possible with further analysis. The "spiral arm" feature blows slowly away from the nucleus, with a velocity around 700m/s, getting fainter as it gets further away.

Animation developed by M.R. Kidger, M. Serra-Ricart, R. Casas.

red_dot.gif Arm Formation Animation (MPEG, 218K)
red_dot.gif Arm Formation Animation (MPEG, 27K, Aug 31, 1995)
red_dot.gif Arm Formation Animation (MPEG, 38K, Sep 6, 1995)

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