Monday 4 February 2008

2008 January notes: 2005 BT1, BI10604, 2007 XS16, 2008 AV72 = 2000 JF4 = 2006 PH11

January was rather disappointing with fewer hours logged observing than for the same month in any of the previous 5 years.

A highlight was the recovery of the Apollo 2005 BT1, originally discovered by LINEAR on 16 Jan 2005 and followed for 47 days. Predicted to have a favourable approach in Jan 2008, a search was started from Great Shefford on Jan 24th, the expected magnitude given by the Minor Planet Center was +19.1 and the likely uncertainty area given as over 8 degrees long, aligned almost North-South.

I covered the central 4 degrees with my 18'x18' field of view during 24/25 Jan and extended this to the N by another degree on 26 Jan but searching was cut short by clouds. Only 0.5 degrees was added to the S the next night before clouds interrupted again, but finally on 28 Jan, on the first attempted field that night the NEO was finally caught, 2.35 degrees off track to the south. It had taken 814 images taken on the four nights, of 30 separate fields to locate it.

The next night was cloudy again in the UK so I contacted Sergio Foglia (IAU code 147) and Luca Buzzi (code 204) in Italy to see if either of them had good skies to try and get a confirming second night of positions for it. Sergio was not able to observe but Luca managed to get some astrometry before he too was clouded out. With the positions from 2008 Sergio then searched for possible images from the old SkyMorph image archives and managed to locate it faintly on two images from 07 Jan 2002 taken with the Palomar 1.2-m Schmidt. All three sets of positions were sent off to the MPC and within the hour MPEC 2008-B60 was issued formally announcing the recovery.

Another extensive search that didn't end up with such a positive result was also a LINEAR discovery found at 03h UT on 16 Jan and posted on the NEO Confirmation page with temporary designation BI10604 just after midnight on 17 Jan. Although relatively bright at mag +17, by the time I could observe on the evening of 17 Jan the uncertainty area was a 1 deg x 2.5 deg oval. I covered the whole area with multiple images being taken of 31 different fields, but did not find it. By the end of the 4 hour session the area had already expanded by a further 0.5 degrees. It never did get recovered by any observatory and two nights later was removed from the NEOCP...

A good set of luck came my way on 7th Jan while I was following up on one of the main belt discoveries I had made in December (2007 XS16). I found a very faint moving object, about mag +21, that did not match any known object and so measured positions of it. I had hoped to try for it again in the coming nights and send in two nights of astrometry to the Minor Planet Center, but clouds stopped any further attempt for over a week. By 17th Jan I decided to just send in the positions as a one night stand (ONS), expecting that I would not hear any more about it. However, by the next day the MPC had managed to match it up to a ONS from the 1.5-m reflector of the Mt Lemmon Survey obtained 5 days after mine on 12 Jan. It was designated as 2008 AV72 and I was given discovery credit for having the earlier of the two ONS!

With this extra data I now realised that other images taken of 2007 XS16 from the previous month might include 2008 AV72 and on re-examining these managed to find it on images taken 29 Dec and then 19 Dec 2007. After these pre-discovery positions were sent in, the MPC quickly managed to find various other ONS back to May 2000 and even two occasions where the object had been given a designation on the basis of two nights of observations (not enough to determine a proper orbit), these being 2000 JF4 and 2006 PH11. Because 2008 AV72 had a 2 month observed arc in 2007/8 it was retained as the primary designation and with observations at 5 oppositions and an MPC uncertainty code of 1 it is now in a state where it could potentially get numbered - not bad for just sending in the ONS from 07 Jan having lost hope of being able to find it again!