[BAA Comets] A new outburst of Comet 17P/Holmes

[RICHARD MILES]

Comet 17P/Holmes is a fascinating comet having drawn our attention bigtime 
when it underwent a superoutburst brightening ~14 magnitudes on 2007 October 
24. Interestingly, although its activity subsided, it did exhibit a clear 
outburst on 2009 Jan 04. The exact date is known thanks to monitoring by 
Luca Buzzi at Schiaparelli Obs. and by Richard Miles and George Faillace 
using the 2.0-m Faulkes Telescope North.  The photometry can be seen here:

http://www.britastro.org/~rmiles/Images/17P_2008-9_photometry.png

In 2010 October, the comet reached aphelion at r = 5.188 AU and since then 
it has been approaching the Sun at an ever-increasing rate.

The latest news is that although the cometary nucleus is still about 4.4 AU 
from the Sun, it has just undergone another distinct outburst, brightening 
by some 1.3 magnitudes as observed using the 2.0-m Faulkes Telescope South. 
Here is the photometry as measured using an aperture radius of 2.4":

Date       R mag
Apr 13    21.1
Apr 19    20.9
May 15   19.7
May 17   20.1
May 18   20.2

The outburst probably occurred on 2012 May 12+/-2 as deduced from images 
taken on each of the above 5 epochs. See:

http://www.britastro.org/~rmiles/Images/17P_2012May_outburstA.png

Comet Holmes has some unusual characteristics.  It is likely to be a very 
slow rotator: one unofficial estimate is a rotation period of 44+/-2 days. 
Observers located in the southern hemisphere may find this object to be a 
rewarding target for study. Its current apparition comes to an end in about 
August but the next one (2013 March - 2013 September inclusive) will be 
favourable.  Perihelion occurs near solar conjunction in 2014 March and it 
then moves northwards occupying a similar region of the sky to its famous 
2007 apparition.

Given that the 2007 superoutburst was much more energetic than its outburst 
on the occasion of its discovery in 1892, the physical integrity of the 
cometary nucleus may have been compromised in some way so we may have to 
expect the unexpected from this object during the next few years.

Assistance from the Faulkes Telescope Project led by Dr Paul Roche is 
gratefully acknowledged (see for example: 
http://en.wikipedia.org/wiki/Faulkes_Telescope_Project ) and without which 
none of this work would have been possible.

Richard Miles
BAA