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Teide Observatory Spiral Jet Animation


Spiral jet movie from the IAC80 Telescope. (October 27, 1995)

New Spiral Jet in Comet Hale-Bopp

The images presented here show the evolution of a large eruption on Comet Hale-Bopp, the third to be picked up during the 46 nights of monitoring (to October 23rd) carried out at Teide Observatory. Each frame of the animation is the sum of from 4-9 exposures in broad-band R, each of 300s duration. Some of the exposures were taken at very high airmass through thick cirrus, hence the rather variable quality. The comet is visible for approximately 40 minutes at the start of each night at present and this time is reducing night by night.

The images from each night are flat fielded and corrected for the overscan. They are then examined and poorly guided or unusable images are rejected. The remainder were recentered and processed with a gaussian and then Laplacian filter to bring out the fine structure around the nucleus.

The first image in the animation is the quiescent nucleus observed on October 11th (frame 1). The structure leaving the nucleus is a faint star trail. On October 14th (frame 2) a spectacular spiral structure is now observed. We have no data from the 12th or 13th, but estimate that the outburst started approximately 24 hours before this image was taken.

On the 15th (frame 3) the spiral structure has developed quite significantly and the end of the arm has separated significantly from the nucleus. Unlike the two previous jets, both of which were in PA 280 degrees, this event is most obviously leaving the nucleus in PA 000 degrees.

The image taken on the 16th was spoilt by having a very bright star trailing exactly through the position of the jet. No useful information can be recovered from this image at all. When next observed, on the 18th (frame 4), the jet has changed considerably. Some of the observed structure may be biased by the presence of the bright star trail passing through the nucleus. We see a quite strongly collimated beam in a position angle close to 000 degrees, with a suspicion of an east-west hood.

We see that, between frames 3 and 4, the collimated section of the jet has distanced itself considerably from the nucleus. After frame 4 the expansion of the jet stops and, in some nights, it even seems to retreat a little.

On the 19th (frame 5) the jet has apparently changed quite considerably: there is a broad stream of material to the north, which breaks to the east, although the eastward structure is somewhat indistinct. On the 20th (frame 6) the jet appears similar to the image on the 18th with a narrow northwards beam and a well-defined eastern extension. The structure leaving the nucleus to the southwest is a faint star trail.

The image from the 21st (frame 7) is strongly influenced by a bright star trail passing through the nucleus, the eastwards extension seems to be lengthening and is twisting northwards, the PA of this section having increased considerably since the jet was first observed. On the 22nd (frame 8) the collimated section of the jet again seems to have increased in brightness and the arm is fading significantly.

In the penultimate frame (frame 9), taken on the 23rd, in very poor conditions (the exposures were hand-guided because the cloud was too variable to allow autoguiding), the collimated jet appears quite bright still, although obviously much less so than on the previous night. The eastwards extension is now very faint again its position angle appears to have reduced somewhat again.

The final frame (frame 10) taken on the 25th, shows that the base of the jet is now quite faint, but a clump of previously ejected material, now several arcseconds away from the nucleus, seems to be separating and twisting to the east; this is a particularly interesting image.

No observation was possible on the 26th due to high humidity at the start of the night, but it is evident that the jet is still active and likely to be visible for several more nights. The weather looks promising, at least for allowing us to follow this jet for a few more nights until it is extinguished.

The changes in the morphology suggest that there may have been several venting episodes over the space of a week. Comparison with the high resolution HST images taken on the 23rd will be very interesting and may reveal more about the emission mechanisms. In particular, some models explain the three jets which have been seen since August in terms of three distinct orifices on the nucleus, whilst other models are able to explain all of them with just a single orifice. We believe the former hypothesis, which is supported by mathematical modeling of the rotation and ejection phenomena. This point is critical to the future evolution of the comet and to our guess as to how bright it is going to get.

Images taken by: Ricard Casas, Luis Chinarro, Angel Gomez, Luis Manade, Santiago Lopez and Miquel Serra-Ricart

Reduced by: Ruth Torres-Chico and Miquel Serra-Ricart

Animation by: Miquel Serra-Ricart

Analysis and text: Mark Kidger and Ruth Torres-Chico

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