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Split Comet P/2004 V5 = P/2003 YM159 (LINEAR-Hill)

An account of the discovery circumstances of P/2003 YM159, subsequently renamed P/2004 V5 was given in the initial announcement made on IAUC 8433, published at 20:22UT on 10th November 2004.

Using the 0.68-m Schmidt Telescope of the Catalina Sky Survey (CSS) in Arizona, observer Rik Hill picked up two short tailed comet suspects, less than 2' apart in the morning sky, on four exposures taken between 11:11 - 11:50 UT on 10 November 2004. It was notified to the MPC as a comet suspect and put on the NEO Confirmation page that day at 16:08 UT.

At the Minor Planet Center, Brian Marsden had four positions for each of the two comets spanning just 39 minutes, not enough in itself to work out anything like a good accurate orbit. However, it was obvious from their similar movement that the two objects were related and assuming that they were travelling in essentially the same orbit, but just with a different date when they were closest to the Sun, Marsden managed to determine that the two objects had to be 4.3 - 4.4 AU from the Earth and were in intermediate period cometary orbits.

This extra information allowed him to identify positions previously reported by LINEAR of an apparently asteroidal object on 8th and 24th October 2004 as likely candidates for one of the two comets.

Now with positions from three dates spread over a period of a month, Marsden could then search through old positions and identified the object with one reported eleven months earlier by LINEAR on 17th and 30th December 2003, designated at that time as asteroid 2003 YM159.

It was clear that all the positions from December 2003 and October 2004 were of the brighter of the two components discovered by the Catalina Sky Survey and this was therefore designated component A, the fainter component being designated B, the old asteroidal designation being changed to the periodic comet designation P/2003 YM159

Marsden managed to determine all this in less than an hour and, without any further observations being reported, the object was removed from the NEO Confirmation page at 20:25 UT, less than four hours after being posted and simultaneously IAUC 8433 and MPEC 2004-V52 were issued, announcing the new comets.

However, this excellent piece of detective work might easily not have happened so smoothly, Marsden mentions:

"And this was after our spam remover actually deleted the CSS message--because it included a jpeg image! Fortunately, Kyle [Smalley] was in the office when I arrived and mentioned it: and he was there only because he had been remotely "observing" for Tim [Spahr] on our telescope in Arizona. Otherwise we might have lost the whole thing! "

As night fell later that same day in Great Shefford, skies were generally clear with some intermittent cloud and the image above was taken just after 4am local time, 17 hours after discovery. Exposures were cut short by cloud, but even so, tails on both comets can be made out.

Further information on this object can also be found on the Major News About Minor Objects site.

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