Monday, December 20, 2010

Update on comet-like asteroid 596 Scheila

The coma surrounding 596 Scheila imaged with global rent-a-scope G-2 instrument on 14-12-10. Image is a stack of 9 x 60 sec exposures stacked in ImageJ, then SUMMED, inverted, contrast enhanced and despeckeled.

After my initial attempt to image the coma around 596 Scheila with a short image stack at astronomical twilight, I though that a deeper stack well before twilight would have better results.

Well, as you can see the result is not so good. I was trying to match the sensitivity and resolution of the G7 instrument with a narrower filed of view, hoping to wring more detail out. It didn't work. Why not use the G7 instrument itself? Logistics of work and family meant it was shut when I had imaging time.

The coma surrounding 596 Scheila imaged with global rent-a-scope G-11 instrument on 17-12-10. Image is a single 120 sec exposure, inverted, contrast enhanced and despeckeled.

I then did what I should have done in the first place. Used the G-11 instrument (but no, I just had to be clever hadn't I). As you can see the coma is well described even in a single 120 sec exposure.

The coma is still well visible 4 days after the initial discovery, in fact it has been observed visually (though a telescope of course). It is still not clear whether this is an ordinary asteroid that has had a collision, or a dormant comet undergoing an outburst. Interestingly, 596 Scheila is one of 4 "T" class asteroids, which have a number of comet like features and are related to "D" class asteroids, which may be captured Kuiper belt objects. 596 Scheila will reach opposition on 3 February, when it reaches magnitude 13.4 . Following Schelia and the evolution of it's coma over the coming weeks should be interesting, and may throw more light on the evolution of comets.

A recent spectrum of 596 Schelia after its outburst is here at John Menke's site, it looks like a lot of dust, apparently. J-F Soulier's images show the evolution of the coma, and another nice image from Francous Kugel, another from Aldo Proiett, Martin Mobberley's G-11 image of the 14th. Finally, Joseph Brimacombe has a nice image and a great animation at his site.

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