Wednesday 6 May 2009

2009 April notes: 2009 DP2, 2009 HH36, 2009 HU11

Along with the monthly crop of new NEO discoveries followed during April, several other interesting objects were also observed:

2009 DP2 was added to the NEO Confirmation page as a slow moving (0.36"/min) 19th mag object on April 3rd, unusual in that it had already been given a provisional designation by the Minor Planet Center (MPC) some 6 weeks earlier (the D of DP2 indicating it had been designated in the fourth half-month of the year). The MPC had matched the discovery observations from Feb 17 & 20th by the amateur run Observatoire Chante-Perdrix (50 miles north of Marseilles) with new observations from two stations of the Catalina Sky Survey on March 27 and 28 and realized the orbit was unusual enough to warrant posting on the NEOCP. With further positions on April 4th and 5th it was found to be a Centaur with a period of 17 years and perihelion distance of 3.8 AU with aphelion out as far as the orbit of Saturn at 9.5 AU though currently it can't get closer to Saturn than about 1.6 AU.

Another even slower moving NEOCP object, 2009 HH36 also ended up being classified as a Centaur, discovered on April 19th with the 0.9-m telescope of the Steward Observatory on Kitt Peak. A nearby faint field star caused me a few problems when I first observed it on the morning of April 20th. With 2009 HH36 moving at only 0.17"/min it would take an hour to move just 10" and so the star was never far away but by the next night it had moved into clear sky and was much more easily seen.

With observations identified back to March 31 and extending to May 5th the orbit is now given with a period of 45 years and perihelion distance of 7 AU. Aphelion at 18.5 AU is at the distance of Uranus, though again it does not get particularly close to Uranus, but can approach Saturn to about 1 AU. It is currently about 9.5 AU from the Sun and due at perihelion in four years time.

In the images taken for 2009 HH36 on April 20th, another unusually slow moving object (0.30"/min) was seen nearby at about mag +20 and a check of the MPC's Minor Planet Checker web page did not reveal any previously known minor planet candidates in the vicinity. The next night, when following up 2009 HH36, this other object was searched for and found close to its extrapolated position.

I sent off the two nights of observations to the Minor Planet Center, hoping to be assigned discovery credit for a possibly unusual new object, only to find out that it had already been given as a discovery (not surprisingly!) to the Steward Observatory discoverers of 2009 HH36 and had been assigned the designation 2009 HU11. It turned out to be a Jupiter Trojan, fortuitously within just a few arc minutes of the even more distant 2009 HH36 at discovery.