[BAA Comets] [comets-ml] Apparent outburst of comet 29P/Schwassmann-Wachmann 1

[Richard Miles]

Thanks Mike for alerting observers to the latest outburst of Comet 29P.

N.B. There is an informal group of comet observers who monitor 29P 
photometrically as frequently as is practicable.
I oversee this, as yet, informal observing campaign, which began in 2014. 
Images are taken either unfiltered, or using Clear/Luminance filter, or a 
red filter (preferably Cousins-R or Sloan r). Some observers analyse their 
own images, others send me the FITS files for me to do the honours.

Recently I wrote a tutorial on "How to Observe Outbursting Comet 
29P/Schwassmann-Wachmann" and this should be shortly appearing on the BAA 
website and later on, in the Comet Section Observing Guide. The tutorial 
gives all the necessary details for observers to image and analyse their 
frames photometrically using Herbert Raab's Astrometrica software.
---------------------------------------------

Re. the latest outburst, our monitoring exercise shows this had the 
following properties:

Time of outburst: 2019 Jun 10.97 +/-0.18 (JD 2458645.47)
Rc mag prior to outburst (nominal 5.35" radius aperture): 16.90
Rc peak mag  following outburst: 15.90
Amplitude:  1.0 mag
Rotational phase at outburst:  0.184 +/-0.003
(Period = 57.71 d, T0 = JD 2455229.98 = 2010 Feb 02.48)

Here is a summary of the observations either side of this outburst. We were 
lucky this time that John Drummond (E94) in New Zealand was able to observe 
29P just a few hours before it went into outburst - otherwise your ZTF data 
would have been next best:
Date                                 Rc mag     Obs Code
2019 06 08.37662           16.97R      W87
2019 06 10.73747           16.92R      E94
2019 06 10.74659           16.91R      E94

2019 06 11.18955           15.91R      K91
2019 06 12.36614           15.97R      W86
---------------------------------------------

I should mention what 29P is up to of late:

The activity of the nucleus exhibits a strong seasonal dependence.
Recent data has confirmed the 57.71-day period details of which were 
originally published in Icarus on the basis of 2002-2014 data (plus an HST 
observation in 1996).

Take this latest outburst: adopting this 57.71-d period, it is the 16th 
outburst to have taken place within the rotational phase range of 
0.012-0.585 during the past 2.3 years. During this time interval, ALL of 
these outbursts were fainter than Rc=15.0.

During the same time frame, a further 25 outbursts have been detected 
outside of this same rotational phase range, 17 of which have been brighter 
than Rc=15.0. The brightest two reached Rc=12.1 and 12.2.

Clearly this shows that during the last few years, one side of the nucleus 
(actually 57% of the longitude range) has only been producing weak 
outbursts. Prior to the current observing campaign, many of these faint 
outbursts were never detected.

I would say that the behaviour of Comet 29P is the most bizarre of any solar 
system body and is yet to be properly explained. It warrants close scrutiny 
for sure.

N.N.B. It would be really good if more folk participated in this effort, 
which aims to detect all outbursts brighter than about 0.3 mag amplitude. 
The comet is accessible far enough from solar conjunction for 80% of the 
time so it makes a good target most nights. Anyone interested can contact me 
offline. Thanks all.

Richard Miles
British Astronomical Association



----- Original Message ----- 
From: "'Michael S. P. Kelley' msk at astro.umd.edu [comets-ml]" 
<comets-ml at yahoogroups.com>
To: <comets-ml at yahoogroups.com>
Cc: "Quan-Zhi Ye" <qye at caltech.edu>
Sent: Friday, June 14, 2019 2:48 PM
Subject: [comets-ml] Apparent outburst of comet 29P/Schwassmann-Wachmann 1


> Hi all,
>
> Based on just 2 Zwicky Transient Facility g-band images from the last
> week, it appears comet 29P has outbursted again.  Differencing the two
> images shows a moderately strong point source component, suggestive of
> an outburst.  Quan-Zhi Ye measured photometry within a 20,000 km
> radius aperture (4.5") for confirmation:
>
> Date (UT), g (mag)
> 2019 Jun 9.46, 17.42
> 2019 Jun 12.45, 16.54
>
> The g-band magnitudes are calibrated to the PanSTARRS DR1 catalog.
> Sorry for the delay, but with only two images, we wanted to be sure of
> our results.
>
> Cheers,
> msk
>
>
> ------------------------------------
> Posted by: "Michael S. P. Kelley" <msk at astro.umd.edu>
> ------------------------------------