New Spiral Jet in Comet Hale-Bopp, this time showing rotation The new Hale-Bopp animation which we attach shows the development of what appears to be a new and extremely bright jet in Comet Hale-Bopp (1995 O1). The comet has been observed virtually every night in September with the 82cm IAC-80 Telescope in Teide Observatory (Tenerife, Canary Islands, Spain). Sequences of 300s exposures were taken in R for as long as the comet was visible each night (horizon limit approximately 20 degrees altitude). The latest images which show the development of the jet were taken on September 25th, 26th, 27th and 28th. They have been flat-fielded and overscan corrected and then aligned to give a constant position for the nucleus. The images were then processed using a standard unsharp mask and summed. All images are looked at individually, and any bad ones (eg: poor guiding) are excluded from the summed image. The animation shows only the images from the last 3 nights. 13 images (total exposure 65 minutes) were taken on the 25th, 4 (20 minutes) on the 26th, 7 (35 minutes) on the 27th and 13 (65 minutes) on the 28th. Since the decay of the spiral jet observed up to September 6th the nuclear condensation has been perfectly circular, with no evidence of any important jet activity. On September 25th we see no significant structure which cannot be explained by small guiding errors in the individual images. On September 26th an elongation of the nuclear condensation can be seen approximately in the east-west axis (PA ~081 degrees, although this value is only poorly determined). On September 27th this elongation has rotated anticlockwise by approximately 45 degrees (PA 035 degrees) and developed considerably into a jet similar to that observed in late August. On the 28th the position angle is 323 degrees and a long bright "spiral" arm can be seen extending clockwise from the straight portion of jet to PA 046; some evidence is seen of a possible faint anticlockwise extension giving a "hood" or fountain. The distance from the nucleus to the breakpoint in the jet (where it starts to sweep in a clockwise direction) is 4.5 arcseconds on both the 27th and 28th. Taking the rotation observed between the images taken on September 27.88 and those on September 28.86 we estimate a rotation period of 4.9 days.
Images taken by: Ricard Casas, Luis Chinarro, Angel Gomez, Luis Manade 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
Teide Observatory Animation (MPEG, 31K)
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