C/2003 T3 (Tabur)

Last Updated -- 2004 March 03

C/2003 T3 was discovered on 2003 Oct 14.4 as a 12th magnitude object in Pavo. Situated at an elongation of 89 degrees from the Sun, it was heading north east at 0.3 degrees per day. Confirming CCD observations were made the following night by John Broughton, David Higgins and Terry Lovejoy. Michael Mattiazzo confirmed it visually and described it as mag 11.9, Dia=1', DC=5

Light Curve

These V magnitudes were derived from my unfiltered survey images and include data from several prediscovery images. Each image was reduced by fitting 40+ Tycho stars (with B-V in the range 0.2 to 0.8) to instrumental mags in order to transform to V magnitudes. Contrary to some suggestions, these data show that the comet has not been fading since discovery. They are also in good agreement with Michael Mattiazzo's visual estimates. Assuming the model is correct, the magnitude at 2004 Mar. 1 should be around 10.2. This agrees with MM's negative observation on Feb 29 indicating that it is was not visible on SOHO images, yet stars down to mag 9.8 in the comet's vicinity were. It will continue to be in SOHO's C3 field until the beginning of April. By that time its magnitude should be around 9.8, so it's possible that it may yet become visible (just barely).

Images

	Image by Justin Tilbrook and Ian Bedford, taken on 2003 Oct 17.5 (approx) using Ian's 30" Newtonian and Justin's SAC-7 CCD.
	My image taken on 2003 Oct 18.45 as the comet nears the13th magnitude galaxy NGC 6848 in Telescopium. 10x20 sec exposure, C11 @ f/5.8 + ST6. N at right, E at top.
	Image by Justin Tilbrook, 2003 Oct 20.5 with 8" Newtonian and SAC-7 CCD. 3 x 50 sec.
	2003 Nov 14.47 - 6 min exposure (18 x 20s) with C11 @ f/5.8 Comet is mag 11.9 visually.

Discovery

This was my first CCD based discovery since abandoning visual searches in 1999. I have often wondered if I stopped prematurely, as several visual discoveries were made in the southern sky while I was busy developing and testing software for a CCD based search. Nevertheless, I persisted with my strategy of searching the far southern sky and was eventually lucky enough to find one.

My methodology and equipment are described here. I have to say that I'm a bit fortunate to have found this comet before anyone else because for the last six months or so, I've been concentrating on a photometry project, with comet and nova hunting a secondary objective. As luck would have it, I had completed a photometric run the previous night. When the following night was also clear, I decided to search for comets. After two hours of scanning images, an object appeared that wasn't present on the most recent reference image.

This is the first confirmation image. When a "re-image" request is viewed, the software circles the area of interest that generated the request. The line running through the image is an overhead power line. Note the image is intentionally defocused; a necessary evil to improve photometric precision when using large pixels and small image scales!
N at left, E at bottom.

A follow-up image taken ten minutes later showed that it was real and revealed a hint of motion. Another image taken ten minutes later also showed consistent motion. Normally the survey images are binned 3x3 for maximum sensitivity (at the expense of resolution and astrometric precision). Having checked that there were no known comets nor minor planets at that position, I took many unbinned (1x1) images over the next hour to determine the direction and rate of motion. It was at an altitude of 50 degrees at the time so I had plenty of time before it would set below my observatory's horizon. I was suprisingly patient to not rush outside for a peek through the scope!

After enough images had been taken to securely determine the direction and rate of motion, I headed outside to attach an ST-6 camera to the C11 in an effort to get some really precise positions for my report to CBAT. After focussing on nearby alpha Pav, I slewed to the field and held my breath as the first 20 sec integration commenced. A 75% sunlit moon was at an altitude of 20 degrees and it was pretty bright outside. I didn't expect to see much. After an agonizingly long digitization and download (about 40 sec) the image finally appeared, showing a fuzzy object in the center of the field!

The ST6 is pretty old by today's standards and takes quite long to digitize and download. In an effort to speed up the focusing procedure, I turned off Double Correlated Sampling as this improves the digitization rate. Unfortunately I forgot to turn it back on for the real images, hence the noisy looking image! Nevertheless, the comet is easily visible at centre.

I continued imaging for about an hour and a half, until the comet had set below my observatory wall. Most of this time was spent back inside at the computer analyzing the images and formatting a message for CBAT. I have to admit that this CCD based discovery was a very different experience as compared to a visual discovery, but no less exciting! While it lacks the immediacy of photons on the eyeball (the beauty of dark skies and lets not forget the freezing cold and mozzies in summer too), in some ways it was a more "complete" experience, as I was able to provide precise astrometry with my discovery report; something I relied on others to do when I was a visual observer.

It was certainly very satisfying to find a comet and also a relief. I've spent over 1000 hours scanning images since my last visual discovery (not to mention software development and testing time). The NEO search program at Siding Spring is in the final testing phase, so the window of opportunity for amateur comet discovery will soon be closing in the southern hemisphere too. This comet arrived just in time :-)

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