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2004 FK5 (Amor at perihelion one week before close approach to Earth)

2004 FK5 was put on the NEO Confirmation page at 23:40UT on 22nd March 2004 with temporary designation AM81167. Already the uncertainty area was about 1.5x1 in size and a search was undertaken at Great Shefford from 23:54 UT on 23 March to 02:21 UT on 24 March 2004 (with a gap for 17 mins in the middle to image the newly announced fast mover 2004 FA5)!

Altogether seven areas were imaged, centred on the nominal ephemeris position and six others, covering almost all of the area that the object was thought to lie in. As each area was completed it was examined using Astrometrica while the telescope was moved to take images for the next area. Each area had 33 short exposure images taken and these were stacked to give two or three images to blink together to try and reveal the object's motion. Using the MPC's variant orbits given on the NEOCP, images were taken centred on the nominal orbit and orbits #21, 28, 38, 40, 47 and 62. Thirteen of the thirty three images taken for orbit #28 were spoiled by cloud.

Nothing was found that night and eventually LINEAR picked up the fast mover the next night. Soon after that the Minor Planet Electronic Circular MPEC 2004-F53 was issued announcing its discovery together with its preliminary designation 2004 FK5. It approached to about 5.7 lunar distances from Earth at 15:30 UT on 23 March 2004.

The search images taken the night before at Shefford were examined when the announcement came through and sure enough images were found on two of the seven runs. Unfortunately, the NEO had been right on the edge of the images taken for the nominal orbit, #28 and #40.

It was so close to the edge of the frames taken for orbit #40 that no measurable image could be detected at all. However, although visible on the nominal and #28 runs it was only visible on half of the images taken, those very close to the edge of frame did not provide visible images. Because of this, none of the runs actually provided images that would have allowed the object to be picked up that first night. More overlap was needed and therefore more sets of images needed to cover the uncertainty area. Another lesson learned...

The uncertainty area is shown below (blue dots are the expected spread of positions as calculated by the Minor Planet Center for 00:00UT on 23 March 2004. The nominal ephemeris position is at X=0, Y=0. The seven black squares are 24'x24' approximate field sizes taken that first night, with variant orbits marked (#0 is the nominal orbit and #28 and #40 are also marked). The NEO itself is represented by the red line showing its approximate movement during the time taken to exposure each set of 33 frames.

2004 FK5 was imaged again two nights later from Shefford, by which time it had descended to -17 Declination, which from Shefford translated to an altitude of just 21 for this fast moving mag +19 object. The resultant picture (above) shows a rather blurry NEO due no doubt to the low altitude.


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