[BAA Comets] Fw: C/2011L4 questions

[Giannantonio Milani]

Hello Denis,
I can perhaps give a small contribution answering only to part of your 
questions


2) How much dust has been released from the nucleus to maintain the large fan tail we have seen and
imaged for so long. Also has spectroscopy revealed the nature of the material released from the
nucleus.

I know the dust production rate can be calculated from inverse tail 
models, but I don't know if someone already did this. Estimates from 
Afrho are also used, but this requires many assumptions on a number of 
unknown parameters and as a consequence the results are not too reliable.

> 3) Has there been a gas component imaged in the tail? The colour imaging has only shown a yellow fan
> with no blue gas feature.
yes I know a gas tail, both ion and sodium tails, have been identified 
in some images. The sodium was particularly strong aroud perihelion.
> 4) We have see and imaged the forward spike/antitail for a month or more now , with little change in
> the PA of this feature with respect to the comet head. I assume that as the viewing geometry is
> changing all the time as we are see the comet moving away from earth. Why is the PA of this forward
> spike/antitail not changing with time? On Comet Arend- Roland the antitail lasted only a few days
> (11 I believe) and was seen to swing round as the viewing geometry changed.
the difference is on the viewing geometry. In comet Arend-Roland the 
Earth crossed the comet orbit and this caused the narrow spike antitail 
with a fast changing aspect. In the Panstarrs case we were far from the 
orbital plane and nearly in the best position to observe at best the 
large fan of the dust tail. We dont' have a real antitail but a very 
wide fan with one edge made probably of old dust placed close to the 
orbital plane.
> 4) What is the cause of the forward spike/antitail, is it just a question of viewing perspective.
yes, usual antitails are due to the viewing perspective. A different 
case is with the so called nech-line features that can develop short 
real antitails. But it is not easy to have the right comet with the 
right observational circumstances to observe a neck-line.

Best regards
Giannantonio Milani
>
> Thank you in advance
> Denis Buczynski
>
>
> _



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