[BAA Comets] Science from visual observations of 29P/Schwassmann-Wachmann: a plea

[Shanklin, Jonathan D.]

There are a few "I" estimates of the comet in the files, and these are mostly immediately after an outburst has commenced, with the comet at DC=8 or 9.  Once the coma becomes diffuse the visual nuclear magnitude is likely to become too dependent on observing conditions to be of much systematic use.  This is one reason why visual nuclear magnitudes are not normally reported, and also why many reported m2 magnitudes are highly discordant.


You might be able to use some combination of the reported visual magnitude, coma diameter and DC to help constrain things, but my opinion is that using visual magnitudes is unlikely to put much of a constraint on the time of outburst.  Of course presence / absence observations do place some constraint.


I think that for the study you are suggesting it would be best to use electronic observations from telescopes in sites with conditions of good seeing and transparency.


Regards,

Jonathan Shanklin


________________________________
From: Comets-disc <comets-disc-bounces at lists.britastro.org> on behalf of Richard Miles <rmiles.btee at btinternet.com>
Sent: 10 December 2016 15:51
To: asvcometsection at yahoogroups.com; BAA Comets discussion list; comets-ml at yahoogroups.com
Subject: [BAA Comets] Science from visual observations of 29P/Schwassmann-Wachmann: a plea

<<Many visual observers subscribe to these mailing groups hence I am sending
a request aimed primarily at them concerning future visual observation of
29P/SW1>>


The tradition for the visual observer is to estimate the Total Magnitude
(m1) and to express this in effect as a V magnitude. That is fine and dandy
for virtually all fainter comets which do not exhibit a greatly extended
tail. But of all the comets we know, 29P/SW1 is the exception to the rule
and I think we need to re-examine how the comet should be observed.

Recent studies have shown that the large majority of dust and debris in its
coma arrives there through episodic outbursts. The duration of each outburst
is very short in that most (>95%) rise to full brightness in 1-2 hours; the
source of the outburst having effectively shut down early on in the
process.**

When studying 29P/SW1, amongst others, two pieces of information of value to
science are; (a) the time of each outburst, and (b) the brightness of the
pseudonucleus (i.e. the immediate region close to the actual nucleus). So to
maximise the scientific value of the observations, visual workers should
consider submitting TWO reports: one of the Total Magnitude and a second one
giving the Nuclear Magnitude (m2). Clearly, whilst the normal observing
methodologies for an extended source are suitable for the former, a method
akin to variable star observation would seem more applicable when estimating
the latter.

***I would be grateful for any feedback from visual observers as to how they
might go about elaborating their observing methodology specifically for
29P/SW1.***

I should add that although the comet has been a difficult target tracking
through the southern Milky Way during the last few years and is now reaching
the end of its current apparition (solar elongation ~37 deg and decreasing),
from next year until the end of 2020 it will lie within 16 degrees of the
celestial equator where it will be easily observable from both northern and
southern hemispheres. 2017 will therefore be a good time to adopt an
enhanced observing methodology for this comet to maximise the science yield.
It would be good therefore if some mutually agreed approach to Nuclear
Magnitude estimation could be arrived at in the near future to be adopted by
visual workers.

Thanks in advance.

Richard Miles
British Astronomical Association



** P.S - Given this scenario, the use of the Afrho parameter to describe the
activity of 29P/SW1 is only a proxy parameter for dust production since
A'Hearn's model is based on continual supply of dust to the coma; for
instance, it is often equated to dust production rate expressed as kg/s.
This topic could be another discussion thread ...

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