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

[Richard Miles]

<<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 ...