Partial lightcurve for 2012 DA14

On the night after closest approach, when the apparent motion had slowed down to around 15"/min and magnitude faded to about +15, three hours of photometric observations were obtained, the diagram below indicating that just a part of the overall rotational lightcurve had been captured, showing a rise to magnitude +14.3R, followed by a fall to +15.9R.

Radar results for 2012 DA14 obtained from NASA's Goldstone facility and qualified by Dr. Lance Benner on MPML indicate a rotation period of "probably somewhat longer than 8 hours".

2012 DA14: 3 hours of lightcurve covering 2013 Feb. 16th 21:10 UT  - 17th 00:11 UT
PPMXL catalogue used for reductions, error bars derived from measured S/Nr are shown

Update 20/2/2013 20:35UT: A much more complete lightcurve by Bruce Gary from Hereford Arizona Observatory (G95)  can be seen here, covering about 10 hours of observing, yielding a rotation period of just over 9 hours.

2011 August notes: An amateur discovered tumbling NEO

August continued the poor run of weather from July and most of the time it was a case of making the best of what clear sky there was.

One opportunity came early in the morning on August 9th when a new discovery was posted on the NEO Confirmation Page, eventually designated as 2011 PE2, this one picked up by the amateur run La Sagra Sky Survey in Spain. The discovery images were from 24 hours earlier which was quite unusual, often La Sagra post their discoveries in near real-time. Jaime Nomen from the survey mentioned later that their reduction software had crashed during the previous evening and those images that had not been processed at the time were put into the queue for the next night, so it was only detected a day later.

Because of the delay the positional uncertainty was growing, with the Minor Planet Center's uncertainty map indicating the likely area it might be found in was 1.75 degrees long. I eventually picked it up 20' from the nominal prediction and then followed it for 20 minutes to get enough images to measure astrometry to send to the MPC. The ephemeris indicated it should be about mag +18.3 but during that 20 minutes it could be seen to vary in brightness from barely visible to very obvious within about 10 minutes. Because of this, I decided to continue to follow it until dawn to try and obtain a lightcurve, ending up with nearly three hours of measurements and showing the total variation to be very large at about 2 magnitudes (a factor of 6). 2011 PE2 was about at its brightest when discovered and on subsequent nights had already faded too much for any more useful photometry to be obtained.

Canopus was used to reduce the brightness measurements obtained that first night and to plot a lightcurve. Although the rises and falls from max. to min. in approx 10 minutes that were noticed at the time the images were taken were visible, the variations were not regular, indicating that it may not be simply rotating in one axis, but probably tumbling. In the diagram below, "beating" can be seen in the maxima and minima as two competing periods cause constructive and destructive interference to the overall curve, indeed at about 0.57 on the x-axis a minimum is almost completely absent.

Solving for a single period gives a value of 43.8 minutes for the main variation (so 11 minutes between each maxima and minima). However, the second period has not yet been satisfactorily determined and so the final value of the main period is still undetermined and could be somewhat different to that given above.

Raw (unfolded) lightcurve of 2011 PE2 from 348 data points obtained 2011 Aug. 09 00:14-03:08 UT

2011 April notes: 2011 GP59 and NEOCP changes

April continued the good spell of weather that set in during March and ended up being the warmest April since records began for the British Isles. Plenty of Near-Earth asteroids were picked up by the surveys but probably the most interesting object was 2011 GP59 which was discovered by the amateur run La Sagra survey in southern Spain just before midnight on April 8th. It was described as mag +17 by the discoverers and was heavily observed from Europe in the next few hours, with 45 positions being reported by the time I sent my first position in, just 2 hours after discovery. It was immediately obvious that it was varying greatly in brightness in the space of just a few minutes and it could be seen to brighten up and then fade completely from view in real-time as sequential images were captured and displayed on the pc. Also evident early on that first night was that it would brighten over the coming days and make a close approach about a week later. It passed Earth at 1.4 Lunar Distances on the evening of April 15 but at a southerly declination and running into evening twilight so difficult to observe from the UK. Nick James posted a very good animation on YouTube showing the rapid brightness changes from the night of April 11th.

I last observed it in the early hours of April 12th when it was 16th mag and still moving relatively slowly at 9"/min., obtaining 376 images over a three hour period to try and determine a lightcurve. The initial reduction of the data showed a dramatic curve with a 2 mag amplitude and a period of just over 7 minutes. However, there was quite a noticeable scatter in the brighter segments of the curve, just where the errors would normally be expected to be at their smallest.



Initial lightcurve reduction, showing large scatter at the brightest part of the curve, where scatter would normally expected to be least



So Canopus was used to try and determine whether the object was tumbling and if a secondary period was contributing to the scatter of the main curve. Canopus has functionality to determine an initial lightcurve and can then subtract that modelled variation from the original data points. The adjusted data points can then be used to try and solve for a secondary period. If a secondary period is apparent, then this can in turn be subtracted from the original data points and a fresh determination of the primary period  made. A few of those iterations for 2011 GP59 resulted in the two lightcurves shown here, the main one with a 7.352 +/- 0.002 minute period and 1.8 mag amplitude, while the secondary period was found to be 10.25 +/- 0.02 minutes with an amplitude of approximately 0.4 magnitudes. There is a great deal of scatter throughout the secondary lightcurve and it is best viewed from several feet away(!) when the sinusoidal lightcurve becomes much more apparent. The overall noise is mainly due to the secondary period being superimposed on the large 1.8 magnitude variation of the primary period and therefore both the maximum and minimum of the secondary curve have data points contributed from the faintest parts (as well as the brightest parts) of the overall variation, so low signal/noise ratio measures, with large scatter are unfortunately present throughout the secondary curve.



Primary lightcurve with secondary subtracted



Secondary lightcurve with primary subtracted

Using measurements obtained by the Lowell Observatory from the previous night, tumbling asteroid expert Dr Petr Pravec reported similar results in the Minor Planet Mailing list here http://tech.groups.yahoo.com/group/mpml/message/25234 with periods of 7.3501 +/- 0.0004 minutes and 10.258 +/- 0.003 minutes.

Users of the NEO Confirmation web page will have noticed during late April that the number of objects on the page has exploded from what in previous months had been at most around 30 objects at any one time to much higher numbers, for a while in the first few days of May there were over 160 objects listed. The surveys are not necessarily picking up any more NEOs than they had done a few days earlier, rather the Minor Planet Center (MPC) has changed the threshold "NEO probability" that a newly discovered object has to score to get onto the page. Following a workshop in March that included representatives from all the NASA funded surveys, JPL and the MPC, the attendees overwhelmingly voted for more objects to appear on the page, so objects that only have a small chance of actually being a NEO (such as objects with Mars crossing orbits, Hungarias, Phocaeas etc.) are now appearing on the NEOCP along with more definite NEOs.

As an observer, the sheer number of objects on the page makes target choice very difficult and to help, the MPC are making some modifications. Initially they have started displaying the NEO probability as a percentage against each object, so the observer can choose objects with high scores, say 50%+ if they want to have a good chance of observing a new NEO. In beta test now and hopefully soon to be introduced fully is a means of filtering the page by magnitude, declination and NEO probability which should make planning an observing session much easier.

2010 XM56

December and November were very disappointing months, the smallest amount of clear skies here for seven years, indeed my counts of nights used (169) and hours spent imaging (702) for the year were also the lowest since 2003. I recall writing this time last year how 2009 had produced the best observing figures since my observatory was commissioned in May 2002... I should have kept my mouth shut!

On one of the rare decent nights in the month, I followed Apollo 2010 XM56 for 5.9 hours on December 16th. It had been  discovered a week earlier by LINEAR and with an estimated diameter of only about 30 meters it was predicted to reach mag. +15 as it passed by Earth at slightly less than 2 Lunar distances. During the night its apparent speed accelerated from about 160"/min up to 250"/min and only stayed in the same field of view for 4 minutes at the start of the night and 3 minutes by the end. It was obviously varying substantially in brightness with a period of about 2 hours. I stacked all the usable images from each of the separate fields of view taken during the night and ended up with 96 photometric measures. The raw lightcurve shows a plot of relative  magnitude against fractional Julian Day (0.5 = December 17.0 UT) and shows the amplitude of the brightness variation increasing from an already substantial 2.5 magnitudes at the start to 4.4 magnitudes by the end of the night! By the end, the object was changing from being very well recorded on individual 2 second exposures at maximum, then fading within 1/2 an hour to being completely invisible on individual images at the deep minimum, though the multiple image stacks made at minimum still recorded it well. Some of the increase in amplitude will be due to the rapidly increasing phase angle (47° increasing to 65°) as shadows lengthened on the surface of the object although there may also be some variation due to tumbling. The period was determined to be 2.35 +/- 0.02 h.

Raw lightcurve of 2010 XM56 from 2010 Dec 16/17th

Chang'e 2 booster

Here is a lightcurve derived for 2010-050B which appears to be the booster that helped launch the Chinese Chang'e lunar mission. It was on the NEOCP for a while and looks like it will be visible for a while at least as a NEO-like distant artificial satellite. The lightcurve is from 246 exposures taken on 25 Nov. which shows a 26.89 sec rotation period with an amplitude of about 3.0 mags and I interpret it as representing a generally regular, elongated object, but as the "dark" ends point towards us, one end produces a bright (2+ mag) flash, lasting just 2.6 seconds centered at about phase=0.56 and the other end produces a much fainter flash (<1 mag.) for about the same duration at phase=0.06.

Lightcurve of 2010-050B (the booster for the Chinese Chang'e mission)

2009 October notes: 2009 TM8, 2009 UD, 2009 UV18, LCROSS and 9U01FF6

Apollo 2009 TM8 made a very close approach to the Earth early on Oct. 17th about 48 hours after discovery by the Catalina Sky Survey. It was followed from Great Shefford from soon after sunset on Oct. 16th when it was moving at an apparent speed of 180"/min, through to 04:20 UT the next morning by which time it had accelerated to 285"/min. It reached its closest to Earth at 03:37 UT at a distance of 0.9 LD. The brightness stayed fairly constant, around mag. +17.5 all night, the decreasing distance from Earth being offset by increasing phase angle but the large increase in apparent speed made it a more difficult target as the night wore on.

Another newly discovered Apollo, 2009 UD passed Earth at 2 LD on Oct. 20 and was observed on the morning of Oct. 17th for 2 hours and again for 3 hours the next morning when it was at about 3 LD and mag +17.0. Over 1,000 images were obtained in those 5 hours and allowed the determination that this ~15 metre diameter object rotates very fast with a period of 83.7 seconds with an amplitude of about 0.7 magnitudes.

2009 UV18 was an interesting LINEAR discovery from Oct. 22, relatively bright at mag. +18 and unusually large for a new discovery, estimated at over 2 km diameter. With a low inclination and the Earth approaching the ascending node of the orbit the size of the orbit was initially rather indeterminate and attempts at trying to identify it with a known minor planet failed, even though it ought to have been relatively bright in earlier apparitions. Then, on Oct. 29, Rob Matson, well known for precovery work with online image databases managed to find it on old NEAT images from Jan 2004, fortunately only 2.5° from the predicted place, even though the uncertainty was estimated at up to 90°.

The orbit of 2009 UV18 is similar to a Jupiter family comet and although it appeared stellar in images taken on Oct.23 and Oct. 26th it is probably worth keeping an eye on as it approaches perihelion this January in the morning sky. The last favourable return appears to have been in May 1993 when it should have reached mag. +16 and before that spring 1976 at mag +17.

The LCROSS mission was followed one final time on the night of Oct 8/9th. The spacecraft was only 6.4° from the gibbous Moon and internal reflections in the telescope made it a difficult target. Unfortunately the sky clouded over before the LCROSS shepherding spacecraft separated from the Centaur at 02:50 UT, the last images obtained that show LCROSS were taken at 01:56 UT but were so light polluted they could not be measured. The image of LCROSS was taken about an hour earlier, before the glare from the Moon became too strong, less than 11 hours before impact with the Moon.

What initially appeared to be a Near Earth Asteroid discovery was reported by the Catalina Sky Survey on Oct 26 and received their temporary designation 9U01FF6. It was 19th magnitude and moving at 10"/min but was already closer to Earth than the Moon. After follow-up from other observatories that same day it was found to be in a very unusual 31.5 day period, highly eccentric geocentric orbit, taking it to within 82,000 km of Earth (0.2 Lunar Distances) at perigee and out to 761,000 km (2.0 LD) at apogee. With an absolute magnitude of +30.9 it would only be 1-2 metres in diameter if it were a natural object, but smaller if artificial (with a higher albedo assumed). Further observations were made from Great Shefford on the evening of Oct. 27th and the last positions reported this perigee came from the OAM Observatory at La Sagra in Spain early on Oct. 28th.
9U01FF6 is fainter than mag. +21 for most of its orbit but will next be at perigee around Nov. 28th and should reach +16th magnitude but moving as fast as 250"-500"/min on the evening of Nov. 27th. Hopefully it will be recovered in the days leading up to that but observability is probably limited at most to only 2-4 nights each perigee. It is likely to be an unusual artificial satellite but further observations at the end of November are encouraged.

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