C/2011 W3 - Discovery Account
- Thanks to everyone for all the kind comments regarding my discovery of C/2011 W3!
I'm still quite stunned by the fact that W3 is a Kreutz Sungrazing comet. This is a very special discovery to me as I have long been fascinated by the Kreutz Sungrazing comets. During the 1980's I generated a number of Kreutz Sungrazer search charts that were published in "Perihelion" the quarterly bulletin of the Australian Comet Section. This followed from a spate of Kreutz comets that appeared in choronographic images taken by the Solwind and Solarmax missions. Despite intense ground based efforts at the time to search for Kreutz comets none were ever found. Fast forwarding a little to the mid 1990's the SOHO mission was launched, and it's choronographic images were published on the internet in realtime. As result SOHO Kreutz fragments were discovered at a rate of several per week by a dedicated group of comet hunters. In fact I found a few of these objects myself. However, none of these objects were ever bright enough to be see from the ground, except for C/2008 O1 which was successfully imaged during a Total Solar eclipse on Aug 1, 2008 (see http://www.zam.fme.vutbr.cz/~druck/Eclipse/Ecl2008m/Tse2008_200_mo1/00-info.htm ).
Anyway to the discovery of C/2011 W3, it was the first comet I have found with my new equipment setup. I now use a C8 Schmidt-Cassegrain scope working at f2.1 with a QHY9 CCD camera. This gives me a field of view of a 4.5 square degrees which although only 1/8th of that of my previous DSLR camera, more than makes up for this in extra sensitivity. As a result I can cover the same amount of sky to perhaps a magnitude deeper. Despite this it has been over 4 years since my last discovery and I do hope the next one comes a lot sooner!
The actually discovery images of W3 were made on November 27.7UT, 2011 (Wednesday morning local time). On that morning I imaged some 200 different fields with 3 images each, taking about 2 hours to fully process. After processing, I began searching and on one set of images I noticed a rapidly moving fuzzy object. As I was unsure this was real, I noted the positions and wrote a brief comment "Possible reflection" before proceedind to search more images. The next night I decided to investigate further the suspect since its position, shape and motion didn't appear consistent with an optical reflection and for this reason I decided to make a followup observation.
On November 29.7 UT I began an imaging sequence around the estimated position of the object. However, if the object was real it was travelling very rapidly at 3 degrees per day so any uncertainty in the direction and speed would mean the estimated position could be in error by a couple of degrees. Furthermore cloud and haze hampered imaging that morning. Nonetheless, I was able to capture 6 images that showed a faint but definite fuzzy object near the expected position. Additionally the fuzzy object was consistent in both motion and appearance to the object found 2 mornings earlier. At this point I sent out a request for independent confirmation to a number of trusted observers.
On November 30, all recovery attempts were thwarted for many reasons including weather and insufficient limiting magnitude. Interestingly though, Michael Mattiazzo made a comment that he felt the observed positions were similiar to that of a Kreutz sungrazer. Then, finally, on December 1 I recieved an email from Alan Gilmore stating that he and Pam Kilmartin had successfully imaged the comet with the 1 metre telescope at Mt John Observatory. A few hours later I also managed to get some followup images. The object was then published on the NEO confirmation page before being susequently officially announced in CBET 2930/2931 on December 2.