Re: [comets-ml] Fw: C/2011L4 questions, and answers
- Denis - Uwe Pilz interpretation of the situation re PanSTARRS' current
appearance is essentially correct. In my opinion comet 2011 L4 looks precisely
like what would typically be anticipated for a very dust-rich comet under
the prevailing viewing geometry.
The comet is not displaying any sort of actual antitail, or anomalous
tail. What is seen is simply a continuous fan of material with no clearly
independent/separate sunward-pointing feature. The tail is best classified as
just a very broad dust tail of Type II, or combined Type II and III in terms
of the old nomenclature. Actually, we have seen a number of such situations
presented in fainter comets over the past decade, or two, and I think many
here may well recall some of them.
From the Earth's perspective the comet is very close to being situated
diametrically on the opposite side of the Sun from us. Therefore, material
trailing the nucleus is viewed with the comet's orbital plane presented
virtually edge-on and the material is seen projecting away from us (just the
opposite of the situation with Comet Arend-Roland in 1957).
The general appearance of PanSTARRS' tail does not even require the
heaviest of the dust to actually lay along precisely the same orbital track as
the nucleus. Rather, it can be located a significant distance beyond the
orbital track of the nucleus and be curving away. It is simply our view along
the line of sight in the orbital plane that gives the current impression.
Even if truly gently curving away from the nucleus it will appear from our
current vantage point as presenting a straight line of demarcation along the
tail's boundary. If some of our imagers would include large and precise
orientation marks on their photos it would help in ascertaining approximately
how much beyond the comet's actual orbital track the extreme trailing edge
of the dust tail material lies.
Concerning the near lack of an ion tail for Comet PanSTARRS, this
exemplifies just how drastically low the gas-to-dust ratio has been for this comet.
Evidence of an ion tail did present itself, if only briefly, during the
interval when the comet was nearest its perihelion passage. Take look at
several of the images uploaded near to that time in our ML image page, there an
weak ion tail will be seen.
Incidentally, I believe that I had voiced my concern about this lack of
evidence of any high gas production long before the comet brightened up and
its likely implications for an ultimately poor performance post-T (the same
seems currently true for Comet ISON as well).
In a message dated 4/18/2013 4:48:20 P.M. Eastern Daylight Time,
From: denis buczynski
Sent: Thursday, April 18, 2013 9:47 PM
To: COML ; BAA Comets discussion list
Subject: C/2011L4 questions
Could anyone on this list answer a few questions about this comet's
Firstly, has there been an estimate of the physical size of the nucleus?
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
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.
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.
4) What is the cause of the forward spike/antitail, is it just a question
of viewing perspective.
5) Has there been any specific professional observing campaign on this
Thank you in advance
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