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Occultation of SAO 134182 by minor planet (663) Gerlinde - 2003, Feb 13/14

In the night of February 13/14, 2003, the bright 9.0 mag star TYC 4814-00668-1 = SAO 134182 was predicted to be occulted by minor planet (663) Gerlinde, a 104 km diameter body. The calculated occultation path was extremely favourable for Belgium (see figure below). The event was predicted to happen around 19h48m UT.

Sky conditions were quite good over the whole of Belgium. Except for the strong moonlight, the sky was clear and rather stable (but freezing cold). At the start of the evening, it became evident that the occultation was receiving a lot of attention from Belgian amateur astronomers, looking at the number of emails appearing on the "bulletin board" of our national astronomical association VVS.

I decided to attempt "high-speed" CCD photometry to register the 4.7 magnitude drop that would last for about 13.4 seconds. I used an SBIG ST-7 CCD on my 0.35-m f/6.3 telescope, and selected a small CCD image field to considerably speed up the download time. I exposed each CCD image for 0.8 seconds. Add to this a download time of about 1.2 seconds, and I was able to monitor the occultation with a "time resolution" of about 2 seconds. Next to SAO 134182, I made sure to include 1 additional comparison star, that I would use to measure the magnitude drop.

I started my CCD observations around 19h40m UT, and continued till about 20h00m UT. The resulting light curve is depicted below, and clearly illustrates that no occultation was measured with a duration > 2 seconds. The "noise" on the light curve is due to the short exposure time and the faint comparison star.

Several visual observers, spread over Belgium, also reported negative observations. This, by itself, is valuable from a scientific point of view, but I would of course have preferred to actually measure the occultation itself.

One final remark : almost 10 years ago, on January 12th, 1993 to be precisely, I made a successful visual observation of the occultation of PPM 154323 (a mag 9.2 star) by minor planet 1330 Spiridonia (Stamm, J. 1996. Reports of asteroidal appulses and occultations. Occultation Newsletter 6: 221-224). This was the first time such an event was observed from Belgium.