The Discovery story of comets SOHO-98 and SOHO-99

Maik Meyer

Over the past few months I have repeatedly but not regularly looked at the real-time movies of the LASCO coronagraphs C3 and C2 of the SOHO spacecraft. Twice I was beaten by half a day by Jonathan Shanklin. After the discoveries of SOHO-95 by Kazimieras Cernis and SOHO-97 by Jonathan Shanklin I decided to search more thoroughly. On January 29, 2000, I was blinking two hi-res C3 frames, when a faint point of light on the right path for Kreutz sungrazers moved back and forth. I loaded another two frames of the available seuqence from 05:42 to 08:42 UT and blinked all of them in the right order. And, to my excitement, this point of light also moved on the other two frames on the right path. I was almost sure that this must be a sungrazing comet but wanted to wait for another frame. But until noon no other frame was available, so I decided to drop a mail to Doug Biesecker and Brian Marsden, announcing my find. I had to work on the Saturday in the course of preparing a scientific colloquium at the institute where I work. However when I left work with a friend for a pint of Guinness at a local pub at 17:00 UT no frame after 08:42 UT was available. When I came home at 22:30 UT I found that additional frames since 15:18 UT had been added and the suspected comet was clearly visible moving towards the sun. It had brightened since the first frames but lost brightness while approaching the sun. The last frame I was able to detect it in was at 23:18 UT. I e-mailed again Doug Biesecker and Brian Marsden, eagerly awaiting confirmation, which came on Sunday. I had found my first comet - SOHO-98! Independent discoveries by Terry Lovejoy and Michael Oates were announced a day later.

On January 31, 2000, I left the hotel where the first day of our scientific colloquium had just ended at about 20:00 UT and hoped for some news of my sungrazing fragment, however no orbit had been calculated. I looked at the two recent frames but did not see anything, so I decided to go to bed early since I had to get up early the next day for the second day of our colloquium. At about 22:30 UT I thought that I would have a very last look at the two most recent frames. I blinked them and again I saw a faint point of light moving on the right path for a sungrazing fragment. Although believing that this was an artifical point of light I downloaded the next image prior to the two that I already had. The point was still moving on the right path! I downloaded another one. Again it moved as expected. Now I was sure. Now the hardest task had to be done: I had to download all the images until the one on which I could first detect the comet. The Internet connection was so slow that I had to wait quite a time for one of the hi-res images (about 900 kB). Nevertheless I composed a mail to Doug Biesecker and received almost immediately the confirmation of this object - internally designated SOHO-99. The message also said, that Terry Lovejoy of Australia reported the comet almost at the same time. I was at this time so tired and so eager to go to bed that I didn't realise that I had discovered the second comet within 3 days.

This comet was very faint, but it can be seen in the C3 image of 22:18 UT on January 31 at pixel location (302, 402). The SOHO co-ordinate frame has (0, 0) at the bottom left corner of the image and (1024, 1024) at the top right. Pixel co-ordinates can be read using many image processing programmes.