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.

2009 March notes: 2009 DD45, 2009 EW, 2009 FH, 2009 DO111, 2009 FD

March and October are statistically the most likely months for NEOs to be discovered that will make very close passes, within 1 Lunar Distance (LD) of the Earth and this March was no exception.

March got off to a good start with the very close fly-by of NEO 2009 DD45, the picture taken during brief gaps in clouds just after midnight on the 3rd when it was at about 0.9 LD from the Earth. Unusually, it was bright enough to be observed from three days before closest approach (discovery by Rob McNaught at Siding Spring at mag +18.7), reaching mag +10 briefly at its closest when at just 0.18 LD (less than 6 Earth diameters away!), fading to 16th mag by the time I first picked it up, but then still detectable at mag +19 in the rich star fields 10°N of Vega three nights later, somewhat brighter than predicted by the MPC ephemeris.

Even before 2009 DD45 had passed Earth, the next close approach object was queuing up. 2009 EW was discovered by the Catalina Sky Survey on March 2nd and picked up from Great Shefford on March 3.0 and again on March 4.9, before being followed through the night of March 5/6th when it came to within 0.9 LD. It was last detected 30 minutes before closest approach at mag +17, moving at 466"/min, 22° above the northern horizon.

Remarkably, less than two weeks later on March 17th, another NEO, 2009 FH was discovered by Catalina, 28 hours before an encounter that would bring it to within 0.22 LD of Earth. When first picked up at Great Shefford at 19:38 UT on the 17th it was already within 1 LD, mag +15 and moving at the relatively sedate speed of 57"/min. I followed it for 2 hours by which time it was 0.8 LD from Earth and had accelerated to 75"/min. It was last reported at 05:02 UT on 18th March, 7 hours before closest approach, at mag +13 and moving at 250"/min by the Catalina Sky Survey's Mt. Lemmon 1.5-m reflector.

A very preliminary light curve from 220 brightness measurements on March 17th indicates 2009 FH has a rotational period of only 6 minutes 26 seconds, with an amplitude of about 0.3 mags. It made more than 13 full rotations during the 1h 27 minutes the observations span.

There were a number of other objects that made approaches nearly as close as the Moon, notable were 2009 DO111, passing 1.2 LD from Earth early on March 20th, as bright as mag +12 and showing rotational variations of about 1 magnitude by March 19th and also 2009 FD passing at 1.6 LD on March 27, again reaching mag +12. Unusually, this latter object was not discovered by one of the NASA funded surveys but rather by the team operating the La Sagra Observatory in Southern Spain.

2009 February notes: 2009 BL58, 2009 BG81, 2009 DS43

Early in February a few fast movers were observed, Apollo 2009 BL58 had been discovered at the end of January by the Catalina Sky Survey. When first observed on 9th Feb it was mag +17.1 and placed 5° SE of Regulus, moving swiftly SE. It was observed two nights later, 45° further on in Hydra at -25° Dec, a degree S of Alpha Corvus and although still mag +17.7, because of its altitude of only 13° was much more difficult to record. It was just a few hours away from its closest to Earth at 4.8 Lunar Distances (LD) and moving at 70"/min.

Apollo 2009 BG81 was a LINEAR discovery from Jan 31st and picked up on the evening of Feb 1st moving at 51"/min, already as close as 4.6 LD but only 19th mag. It came to 4.4 LD on Feb 2nd and was observed by three other observatories but was not reported after that date. With an estimated diameter of 7 metres 2009 BG81 was intrinsically about 4 times smaller than 2009 BL58.

At the end of the month another small Apollo, 2009 DS43 was picked up on 27th Feb in Sextans, first by LINEAR and 97 minutes later by the Catalina Sky Survey (CSS). CSS reported their observations first and were credited with the discovery. It was mag 18 and moving almost due N at 38"/min. I first observed it on the evening of 28th Feb at mag +17.8 by which time it had accelerated to 94"/min and had reached +39° Dec. By then it was at 6.9 LD and would reach its closest at 3am on 1st March at 6.7 LD. By the evening of the 1st it was at a declination of +76° midway between the Pointers and Polaris, had slowed to 81"/min and receded to 7.4 LD and was fading fast, more than 1 mag fainter than the previous night. The Minor Planet Center didn't receive any further reports of it.