Friday 10 September 2010

2010 August notes: (105) Artemis occultation, NEO discoveries and recoveries

The amount of activity on the Minor Planet Center's NEO Confirmation Page (NEOCP) was as expected, quite low during August, with the telescopes of the Catalina Sky Survey being out of action during the monsoon season in the South-West USA. However, LINEAR picked up a number of new objects, as did the WISE Infrared satellite above the atmosphere.

A LINEAR discovery designated 2010 PJ9 passed by at just under 3 Lunar Distances (LD) late on August 9th but weather only permitted catching it from Great Shefford on the morning of the 8th when it was at 6 LD and 16th mag, moving at 30"/min.

2010 PR66 was another LINEAR discovery made on August 15th and confirmed from Great Shefford later the same day. It was about 18th mag at that time but had reached 14th mag 3 weeks before discovery as it made a 10 LD approach in the evening sky that had gone completely unobserved. LINEAR's discovery was impressive, deep in the rich star fields midway between Sagitta and Delphinus, their search algorithms must be very good. Finding moving objects in rich star fields is something that LINEAR still seems to do better than the other surveys. For me, even knowing where to look, it took some time and many exposures to pick it out from the background stars, just to get a few position measurements.

Another stellar occultation was recorded, this time by (105) Artemis on the evening of August 18th (see details including the drift-scan image here). I recorded an 8 second event and Roger Stapleton in St. Andrews also recorded a positive event. The timings from these, together with three other observers in Europe allowed the 123 x 87km oval shape of the asteroid to be mapped out and the result can be seen on the European Asteroidal Occultation Results page for 2010. Click on the chords link to see the result and the link to the observers list showing all those contributing measurements to the the diagram.
I took some images of (105) Artemis before the occultation and measured astrometry from them, sending the positions of (105) Artemis to the Minor Planet Center. It was only later that I recalled that Artemis had been a target of mine 33 years earlier, from my previous location of Cheam (station 499) where I had submitted a single position from 1977 May 22, taken with a 300mm focal length telephoto lens with a 2x converter on Tri-X film, reduced by hand with the SAO Star Catalogue. That result still sits in the Minor Planet Center database and is now joined by my three (new technology) positions from 18 August 2010!

During a quiet NEOCP period towards the end of the month I set about trying to recover some NEOs that had only been seen at one opposition and were predicted to be having reasonably favourable apparitions now. I managed to locate four objects (2006 FE, 2007 VC138, 2008 TC4 and 2009 PY) on the night of August 30th and the weather held up enough for me to get confirming positions the next evening. I was very lucky with 2006 FE to pick it up by chance in a very rich star field in northwest Aquila in the first set of exposures taken, travelling across a little 1 arcmin void amongst the milky way background. The most challenging recovery though was 2009 PY, 20th magnitude and half a degree from prediction, requiring a number of my 18'x18' fields of view to be searched before finding the tell-tale motion of the faint NEO.