2009 September notes: 2009 SH2, 2009 SN103, 2009 SU104, LCROSS and Herschel

September was a busy time for NEOs, with the Minor Planet Center's NEO Confirmation Page (NEOCP) listing many newly discovered objects during the month. On Sept. 17th and again on 26th more than 30 new and potentially interesting objects were on the NEOCP page and by the end of the month an extra 106 NEOs had been added to the MPC's database.

 

Apollo 2009 SH2 was discovered by Gordon Garradd at Siding Spring on Sept. 18th as an 18th mag. object and was due to make a fly-by of Earth within 3 Lunar Distances (LD) by the end of the month. It reached mag +16 when last seen from Great Shefford on Sept. 29th.

 

Another Apollo 2009 SN103, this one discovered by the Catalina Sky Survey on Sept. 25th was 19th mag., already within 4 LD of Earth and moving at 11"/min. It would reach its closest to Earth (1.2 LD) at about 05h UT on Sept. 28 as it overtook the Earth on its way to perihelion on Oct. 30th. It was observed from Great Shefford 6 hours before closest approach when it had brightened to 16th mag. and had accelerated to a speed of 138"/min. It was also caught the next night in central Gemini, moving slower at 86"/min but with the phase angle increasing very rapidly, it was 18th mag., fading quickly and was a much more difficult target to record.

 

It is estimated that 2009 SN103 is only about 8 meters in diameter. Another close approach NEO discovered by the Catalina Sky Survey on Sept. 27th and estimated at about 20 meters diameter was 2009 SU104. This Apollo has a very eccentric orbit taking it very close to the orbit of Venus at perihelion, out to 4.2 AU at aphelion. At this apparition it was on its way to perihelion in Nov., crossing the Earth's orbit just after the Earth had passed by. It was observed at its closest at 2.5 LD on Oct 1st when it was mag. 16 and moving east to west at 223"/min in Equuleus.

 

Several distant artifical satellites were also followed during the month, including LCROSS on Sept. 12th & 16th before it disappeared into southerly declinations until a few days before its impact with the Moon on Oct 9th. The Herschel telescope was also recorded on Sept. 17th at 19th mag. Ephemerides generated from previous astrometry obtained for this object were useless to try and pick it up again as the spacecraft undergoes frequent orbital manoeuvres to keep it near the second Lagrange point (L2). The JPL Horizons ephemeris allowed Herschel to be picked up without problem, moving at 3"/min.

2009 August notes: 9O0DC57, 2009 QC23 and 2009 QY33

August carried on the very good trend of the first half of 2009, with 18 usable nights providing 96 hours of observing and with plenty of NEO discoveries made by the US based surveys it was a busy month.

On July 30th a fast moving 15th magnitude object found by the Catalina Sky Survey and designated as 9O0DC57 by them was put on the Minor Planet Center's NEO Confirmation page, only to be taken off again the next day with a note "was not a minor planet", normal procedure by the MPC when an artificial satellite is mistakenly picked up as a NEO.
This one though did not match any of the artificial satellites with published orbits. It has a perigee of 18,000Km and an apogee 1/3 the distance to the Moon, making it easily mistaken for a NEO during a close approach.
I followed it over a number of nights during August and on August 2nd managed to determine that it rotates every 5.6 seconds, following it from 00:29 UT into twilight at 03:16 UT. From 00:27 to 01:52 UT it showed a regular 1.5 magnitude variation, but when next picked up at 02:56 UT it was showing a very short flash superimposed on the regular variation, probably less than 1 second long and of about 0.75 magnitudes amplitude. Only about 10 minutes later this flash had increased to about 1.5 magnitudes. The lightcurve is from 495 measurements of 1 second exposures, folded using a period of 5.620 seconds, with the increasing flash marked with curves A and B between phase 0.10 and 0.35. The inset from a 60 second exposure started at 03:21:26 UT shows the object trail 250" long and captures 11 flashes and the secondary maximum can just be made out just to the right of the bright flash.

An 18th mag object moving at 18"/min at discovery and put on the NEO Confirmation page on August 22 turned out to be an very impressive amateur discovery by Noeline Teamo from the Hibiscus Observatory (F84) in Tahiti. Designated 2009 QC23 it was followed at Great Shefford for a week.

Another amateur NEO discovery was made on Aug 27th by the team at the OAM Observatory, La Sagra in Spain, but because it got a low NEO rating by the MPCs automated procedures it never made it onto the NEO Confirmation Page. Team member Reiner Stoss alerted observers that two nights of positions had been obtained and requested further observations via the Minor Planet Mailing List (http://tech.groups.yahoo.com/group/mpml/message/22231). A set of positions obtained just before midnight on Aug 28 from Great Shefford allowed the MPC to announce the new Amor object 2009 QY33 the next day.

2009 July notes: (216523) 2001 HY7, 2001 AA50, 2009 NL and 2009 OF

With the short UK nights combined with the summer monsoon starting in the South-West of the US hampering the survey operations, there were only a handful of new Near-Earth objects to observe in July, but several objects were followed on a number of nights in an attempt to construct lightcurves for them.

Aten (216523) 2001 HY7 was observed on three nights in early July, but poor weather prevented getting enough coverage to find an unambiguous rotation period before it had faded out of range by mid-month.

Better luck was had with 2001 AA50, observed on 6 nights between July 20 and Aug 2, which showed an amplitude of 2 magnitudes. A rotation period of just under 26 hours is looking most likely, though a few more nights are still needed to be certain.

Apollo 2009 NL was a LINEAR discovery made on July 13th and was predicted to be magnitude 17 through the rest of the month. Photometry was obtained on 11 nights from July 14-Aug 2 and at magnitude 17-18 the scatter of measurements on individual nights was up to +/- 0.5 magnitudes but even so a likely rotation period of 25.2 hours and an amplitude of about 1 magnitude was able to be derived (see preliminary lightcurve).

2009 OF was another Apollo discovered by LINEAR, this time on July 17th and was initially listed by JPL and NEODys as a virtual impactor. It was observed on four nights from July 19-25, finally being taken off the risk registers on July 26th.

2009 June notes: Observing statistics, 2009 KL8, 2009 MU, 2001 FE90

2009 has provided some exceptional statistics for Great Shefford so far, more usable nights (103) & more hours used (455) in the first 6 months of the year since the observatory was commissioned in 2002, beating the previous best Jan-June (2005) by 10%. Hopefully the last half of the year will be equally good.

June started with the close fly-by of Apollo 2009 KL8, passing Earth at 5 Lunar Distances (LD) on June 2nd. That night it was moving at 60"/min and fading fast, from 19th to 20th mag. during the course of the night. Two nights before, even though about 30% further away it was about 1.5 magnitudes brighter because of its smaller phase angle and I followed it that night for 1h 45 minutes to try and determine its rotation period. That turned out to be just 2 mins 41 seconds, varying by 0.75 magnitudes and it had managed to complete 32 rotations while I was observing it!

Another close approach occurred on June 24 at 16:50 UT when 2009 MU passed at 2.3 LD. The night before it had been well placed throughout the few dark hours available from the UK and was followed at mag. +16, its speed accelerating beyond 100"/min by dawn. Initial indications are that its lightcurve is irregular, suggesting that it may be tumbling, but further analysis needs to be completed.

The Apollo 2001 FE90 was also observed towards the end of the month. Discovered in 2001 when it reached 18th magnitude, this year it was predicted to brighten to mag. +13.3 as it sped from north to south in the evening sky and was scheduled to be a RADAR target at Goldstone and Arecibo at the end of June. I first observed it briefly following a thunderstorm just after midnight on 26th June and in the 22 minutes before it was obscured behind trees it showed a dramatic variation of over two magnitudes in brightness! I observed it on the three following nights and watched the amplitude reduce to 1 magnitude as the phase angle reduced from 79° to 34°.

The lightcurve derived from about 30 minutes of images taken on the evening of 27 June 2009 is shown, including a mosaic of the images from the same sessions, showing the rise and fall in brightness of the Minor Planet as it trailed (from left to right). As can be seen, the observations cover just a couple of minutes less than one full rotation period.

2001 FE90 - light variations on 27 June 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.