The accidental discovery of Apollo 2002BJ2

The details as to the discovery of Apollo asteroid 2002BJ2 is
relatively short, but the lesson it taught me was not.

I have always been interested in recovering PHAs and 1998FW4 seems
to be a interesting target. At mag. 20.2, it is right at the limit of
my 18" set up. The uncertainty could be +/- several degrees in either
direction, that suite the wide FOV of my system too. The difficulty
was that at 15 Hr RA and -15 degree Dec., it would only be visible
for about 90 minutes every morning and it never rises above 40 degree
above horizon. After 4 nights of trial, there was still no sign of
1998FW4, may be it was fainter than predicted.

On Jan. 21, as usual there was no sign of 1998FW4 during visual
blinking. And I would like to test how well Pin Point could detect
other faint objects that might happen to be in the same field. So I
set the mag. tab of Pin Point to an unbelievable 22 (note 1), knowing
full well that at this level there will be so many possible
false "loners" in all three images and it will make the auto
detection take zillion of hrs to complete. To my surprise the whole
process took only a few minutes (with a 2 GHz computer though) and
there were a few detections. Among them was Y00C62. It's motion was
about 0.87" per minute at PA 140 degree or so. The motion in RA was
not too out of line, but the motion in dec was a bit high. I am no
orbit expert. But from my limited experience in seeing how asteroid
move in images, this mean that this asteroid may have high
inclination. While this seemed interesting, I have my fair share of
interesting MB discovery so I just emailed the whole batch of
astrometry to MPC.

As usual, Tim Spahr processed the batch really fast. He emailed me
back all IDs, along with the six lines of astrometry on Y00C52 and
asked me whether this object was real. With 6 positions obtained by 2
sets of triplets, I was pretty sure it was real. Upon rechecking the
astrometry it was confirm that this was a real object. Pin Point
indicated the mag. to be between mag. 21 to 22. I compared the flux
to a known asteroid in the same images and advised Tim to change the
mag. on the NEOCP page to 20.5. This is NOT data manipulation. I just
didn't want to discourage potential observer that this object is too
faint to observe.

The weather in Jan. so far had been frustrating at 333. On a rare
good night I could detect and report astrometry on 600 moving
objects, and the next day only 450 could be IDed to known objects.
Leaving 150 potential new discoveries. But the next night the weather
was less than perfect and only 30 objects could be picked up. The
whole experience was really disappointing. However, it did allow me
to reflect on the method I used and in the next dark run, a totally
new method to discover MB will be tested. But well all of this
belongs to another article.

With this kind of weather I was worry about spotting this object
again the second night. Well, luck was indeed on my side this time
and I did manage to pick up this object on Jan. 22 too. With only a
one day arc, all Tim could tell me was that nothing normal could fit
these observations, and more observations were need. On the third
night it could be observed again. With a minimum of three well spread
observation some meaning orbit could be tried. Tim came up with an
Apollo orbit but he said more observation was necessary. So far I had
not been too excited by this whole incident. I have NEA discovery in
my mind and I know eventually I will discover one. But I never give
this too much attention as I have other more immediate goals at this
point of time. But I also have to admit that by the third day, it
really got me curious as to what kind of asteroid Y00C62 could be?

I had to arrive at the airport by 6 am so no more observation could
be made. Luckily thanks to Tim again, Spacewatch jumped in to help.
With a 4th day observation, Tim was finally able to conclude that it
was indeed an Apollo. The rough orbit indicated that it has a=2.1 AU
with one sigma error of 0.7 AU! It also had very eccentric orbit
(e=0.66) and high inclination (I=25 degree) and H=17 or so (a
disappointment at first).

I got the news when I was in the New York airport. So after all I
did discover my first NEA and it was a relatively big Apollo!

While waiting for the next flight I draw the Earth's orbit and an
Apollo's orbit on a piece of paper, just to discover something that a
lot of you might already know. If an Apollo has inclination=0, it is
just a matter of time that it will hit Earth. But further rough
calculation showed that on average it will still take about 100,000
year for the two to collide, no wonder funding NEA search has been
such a hard sell to the public.

After all the dusts settled I have to confess that this discovery was
pure luck. I seldom visit this region of sky and I only shot a few
sets of images with hope to recover the faint PHA 1998FW4. While this
effort failed, a fair size Apollo was discovered. If credit has to be
given I think Tim Spahr and Bob Denny's Pin Point has to be mentioned
to share any honor. As to me, it just remind me once again that how
interesting this "sport" (to quote a term used by Roy Tucker) is. At
the end all I want to say that I will find another NEA soon, and this
time it won't be another accident, but a well plan effort :)

Bill Yeung


(Note 1) It is well known that with barely a few photons above the
background, photometry at such mag. is not very accurate. That is why
I set the mag. tab to 22, with the intention to get mag. 21 objects.
This is not a problem with Pin Point.