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 1.5°x1° 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
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.