Tuesday 6 February 2007

2007 January notes: 2007 AG2 = 2004 BO41, 2007 BD

A LINEAR discovery added to the NEO Confirmation page on 8th Jan was eventually confirmed from Great Shefford 2 days later at +69 degrees declination in the evening sky and followed for four nights over the next two weeks at magnitude +18/19. Given the designation 2007 AG2, it was strangely not followed up by any other observatories. Then on 25th Jan I heard from Sergio Foglia that he had identified 2007 AG2 with the NEO 2004 BO41 which had been discovered by LINEAR and observed from 19-29 Jan 2004 and co-incidentally I had observed on several dates that apparition as a morning object, eventually being lost in the twilight.

I had searched for 2004 BO41 a year after discovery on 3rd Jan 2005, covering about 1 degree of sky. It turns out that the actual position at that time was more than 12 degrees further on, so even 12 months after discovery it was hopelessly lost and by Jan 2007 was many tens of degrees off track.

Another interesting object this month, 2007 BD was discovered by Eric Christensen at the Catalina Sky Survey using the 0.68-m Schmidt. It was only 3 Lunar Distances away and already 17th mag, moving at 27"/min. It passed inside the Moons orbit 32 hours later, reaching a minimum distance from Earth of 0.84 L.D. on 18 Jan 2007 at 02:53UT and was well observed from the Crimea-Nauchnij, Gnosca and Modra observatories and also from the Catalina Sky Survey during the 16 hours it remained inside the Moons orbit. It was last caught from Modra 42 minutes before closest approach, travelling at 303"/min at mag +13.
It was then picked up again from Catalina 52 minutes after closest approach.

Unfortunately, during the close approach I was clouded out, but did manage to catch it 2 nights later when it was still about mag +19 and moving at 11"/min. This is quite unusual to be visible for several days on each side of an approach within the orbit of the Moon. It turns out that 2007 BD is an Aten minor planet with an orbit smaller than the Earth's, taking just 230 days to circle the Sun and with an aphelion distance of 0.986 AU it could be argued to be an Apohele (orbit being entirely inside that of the Earth). However, with the Earth at perihelion in January and the object reaching aphelion literally on the day of close approach, it was overtaken by Earth, passing just 200,000 miles outside the Earths orbit, appearing to approach from almost due East and to recede due West so was therefore almost equally well placed for observers for days either side of close approach.