Tuesday 4 December 2007

2007 November notes: 2007 VA85 and 2007 VW266

The first half of November was reasonable, with at least some clear sky on 11 nights, but just 3 nights in the last half, including the obligatory crystal clear sky from dusk until dawn on the night of the full moon ...

An interesting object found on Nov 4th by LINEAR was 2007 VA85, 18th magnitude and placed at discovery in the early evening sky between Cygnus and Lyra, passing through the Cygnus star cloud during the next week. It was put on the NEO Confirmation Page and left there for nearly 5 days while the Minor Planet Center waited to see if anyone could detect any cometary features. In the end it was announced as a minor planet but with a very unusual retrograde orbit - four months after perihelion at q = 1.1 AU, with inclination = 132 degrees and period just 8.5 years. I followed it through the rich star fields of Cygnus on 5 nights, trying to catch it in enough empty sky to see whether it displayed any cometary features. Finally on 23 Nov I managed to get a total exposure of 41m 40s at a scale of 1.1"/pixel but could not detect any activity at all.

A week after 2007 VA85 was discovered, the Catalina survey's Mt Lemmon telescope picked up 2007 VW266. This was much fainter at mag. 21 and I just managed to catch it on a single night. By coincidence, it too turned out to have a short period retrograde orbit and was left on the NEO Confirmation Page for 7 days but again, no cometary features were detected by any of the seven observatories contributing astrometry. It has inclination = 108 degrees, q = 3.3 and period = 12.2 years.

In the Minor Planet Center MPCORB database there are only 18 minor planets listed with retrograde orbits and of those, 2007 VA85 and 2007 VW266 have the two shortest periods, with 2007 VA85 also having the smallest perihelion distance of the 18. In comparison, the comet with the shortest period retrograde orbit currently known is P/2006 R1 (Siding Spring) with inclination = 160 degrees, q = 1.7 AU and period = 13.3 years.

Wednesday 7 November 2007

2007 October notes: 2007 UN12, 2007 US51 and WMAP

October provided 13 usable nights for me, about the same as last year, but with only about half the number of hours spent observing it was a rather disappointing month.

A few interesting objects were observed, 2007 UN12 and 2007 US51 were both discovered by the Catalina Sky Survey soon after passing between Earth and Moon. 2007 UN12 passed less than 6 Earth diameters from us on Oct 17th and was discovered four days later, and 2007 US51 passed about half the distance of the Moon on Oct 30 and was discovered about a day later.

Another object put onto the NEO Confirmation page twice during the month (and on a number of occasions in the past too) was artificial satellite WMAP. Sitting at the L2 Sun-Earth Lagrangian point it appears as a very convincing NEO in close proximity to Earth and with plenty of orbital corrections being required to keep it in position it is impossible to predict accurately where it will be over a period of months. It will probably keep making appearances on the NEOCP as it gets 're-discovered' by the surveys every now and then!

Tuesday 2 October 2007

2007 September notes: 2007 RJ1, 2007 SU1 and 2007 RS1

Plenty of clear nights in September with quite a lot of activity from the surveys on the NEO Confirmation page. Indeed, around September 17th there were 32 objects listed, which may be a record.

Several close approaches were observed during the month, including 2007 RJ1 which was followed for 12 days and ended up at 2.8 Lunar Distances (LD) on Sep 16.1UT moving at 102"/min. 2007 SU1 was seen at 6 LD, moving at 44"/min on Sep 27.0UT.

However, the headline object for me was 2007 RS1 on Sep 4th. This tiny NEO was discovered by Steve Larson using the 1.5-m Mt. Lemmon Catalina Sky Survey telescope just before 6am UT on the 4th. It was unusually faint at mag. +20.4 considering it was already moving at 13"/min. Steve managed to track it for over 3 1/2 hours, by which time it had accelerated to a speed of 19"/min and brightened by half a magnitude.

By the time the sky was getting dark at Great Shefford later that day 2007 RS1 was already closer than 1 LD and moving at 150"/min but had not been reported since the Mt Lemmon observations. The positional uncertainty on the sky was rapidly getting worse and predicted by the Minor Planet Center to be about 3.5 degrees at 20:00 UT (11 times larger than my field of view) and set to double in size within the next 70 minutes. I started trying to cover the uncertainty area, starting at the nominal position, but after taking just a couple of fields got a phone call that I needed to pick my daughter up from Newbury (a 20 mile round trip). All I could do was to set the telescope some distance ahead of the predicted place and let it take images while I was away, hoping that the object might just pass through my 18'x18' field of view. I set the exposure length to 4 seconds which would cause the object to trail if it did pass through, making it more obvious to identify but at the expense of some accuracy in measurement.
Background stars appear as lines of dots as the fast moving asteroid is kept in the centre of the image and itself appears as a small streak due to its own movement during each individual exposure

By the time I returned from Newbury the sky was clouding over for the night but I had amassed a total of 756 images, 564 taken in one long sequence while I was driving. After spending a number of hours searching the images I eventually managed to locate the tell-tale streaks of the NEO speeding through some of the images taken while I was away from the observatory. Remarkably it passed almost centrally through the field of view, taking just four minutes to pass from one side to the other. With the ephemeris corrected I was then able to find a few more images of it entering the field of view at the very end of one of the early runs I took before I left.

The last images that recorded it were taken at 20:39 UT when it was mag +18, moving at 246"/minute and with it 0.55 LD from Earth. It was to pass just 0.19 LD from Earth, or less than 6 Earth diameters away at 01:18 UT on September 5th, but was it was not reported again.

JPL is listing 2007 RS1 with the faintest absolute magnitude of any Minor Planet, with H = 30.98 +/-0.36, the previous record being 2003 SQ222 at H = 29.99 +/-0.70. It is likely that 2007 RS1 is only about 1 or 2 meters in diameter.

Friday 7 September 2007

2007 August notes: 2007 QA1

August saw a rash of new main belt objects picked up from Great Shefford and as I write this four have very good, secure orbits, three others are OK with several weeks of observations and one I only managed to record on two nights and so is effectively lost.

2007 QA1 was another new object I picked up on the night of Aug 16 at mag +19.0 which turned out to be interesting - it was heading almost due south (in p.a. 195 deg) though was not moving unusually fast. I could not identify it with any known object on the MPCs Minor Planet Checker web page. I also checked it against the MPCs NEO rating page to see if it had any chance of being a NEO and that came back with a very low rating of 3% (50%+ is required to get an object placed on the NEO Confirmation Page). I held onto the positions to try and get a second night but the next night was cloudy.

Later that day the MPC added it to the NEOCP, having received positions from the Lowell Observatory. Although it did not end up being a NEO (perihelion distance was just greater than the 1.3 AU limit) it was a Mars crosser and having appeared on the NEOCP from Lowell it was effectively lost to me as a discovery - the first observatory reporting even a single night of observations will be granted discovery credit if it appears on the NEOCP, unlike normal Main Belt objects where it is generally the first observatory to report two nights of positions that gets discovery credit.

Lesson learned: Don't rely on the NEO rating page to decide if an object is interesting! In fact it's motion was very unusual, of the 1794 minor planets that were mag +23 or brighter within 5 degrees of 2007 QA1, only one other was moving in a direction with a p.a. less than 209 degrees. Next time(and I hope there is one!) if another potentially interesting object turns up I will submit a single night of positions to the MPC and let them decide whether it is interesting enough to put on the NEOCP...

Monday 6 August 2007

2007 July notes: Floods, 2007 DT103, 2007 MB4 and recovery of 2001 RV17, 2005 XW77 and 2003 CG11

The continued bad weather here culminated in flash flooding on 20th July which left us with two rooms under water, but fortunately the observatory stayed dry. Since then the weather has noticably improved with a run of good clear nights in the last week of the month.

During the month three NEOs were recovered at their second apparition - 2001 RV17 at the beginning of the month with 2005 XW77 and 2003 CG11 towards the end, both of those two in collaboration with Luca Buzzi at the Schiaparelli Observatory in Italy.

A couple of moderately fast movers were followed over several nights - 2007 DT103 which was detected at the end of the month by RADAR from Goldstone and found to be a binary, and 2007 MB4 that passed at about 8 Lunar Distances on July 5th.

Thursday 5 July 2007

2007 June notes: 6R10DB9's fourth and final perigee

As anyone in the UK will already know, the poor weather in May just got worse through June. I suffered the least number of hours observing since December 2002.

The unusual object with provisional designation 6R10DB9 made it's fourth and final perigee in June. Back during the March perigee it was observed with the 10-m SALT telescope and found to have a rotation period of only 2.75 minutes and an amplitude at that time of 1.2 magnitudes. This time it approached from the sunward side of the Earth, passed over the North pole and was picked up again a day after perigee on June 15th in Draco, about 1 degree from Theta Cep while only 0.80 Lunar Distances from Earth, magnitude +19 - +20 and moving at 47"/min. Never 'bright', it was recorded at mag +18.6 on June 18th and at about +19.5 on the 20th, fading again as it receded from both Sun and Earth. The only other observations reported at the time of writing are radar detections from Goldstone on June 12 & 14 and optical astrometry from the 1.5-m Mt Lemmon telescope on June 22. By the end of June it was below 20th mag and too far south to attempt from the UK.

The main indicator that this object is likely to be natural rather than a piece of artificial space junk come from determinations of solar radiation pressure (SRP) acting on it. Bill Gray's FindOrb freeware program includes routines to calculate SRP, given as the area-to-mass ratio or AMRAT in m^2/kg. With astrometry extending for 10 months now, it gives a value of 0.0011, with an RMS residual from 132 observations of 2.5". Not including SRP increases the RMS residual to an unsatisfactory 9.1". The JPL Horizons orbit solution which also includes the Goldstone Radar observations, gives an even smaller value of AMRAT of 0.0007. In comparison, various distant artificial satellites, such as IMP8, Geotail, J002E3 (the piece of old Apollo hardware discovered by Bill Yeung in 2003), WMAP etc have values between 10 and 50 times larger, indicating that 6R10DB9 is much more massive and much less prone to the perturbing effects of SRP than artificial satellites and is therefore likely to be a rocky body, probably about 4 metres in diameter. There is still a chance that time might be spent at some of the large observatories to get spectra and other measurements during July before it goes out of range completely.

Tuesday 8 May 2007

2007 April notes: 2007 HV4, Comet C/2007 H2 Skiff, 2007 HB5

April provided at least some observing at the telescope on 20 nights, though a fair proportion were of poor quality with haze or moonlight (or both).

Even so there were some notable objects followed. Apollo 2007 HV4 was confirmed on the NEO Confirmation Page during the evening of April 20th, discovered earlier the same day by the Mt. Lemmon operation of the Catalina Sky Survey. When found it was only 5 times further away than the Moon and a difficult discovery at mag +20.5, moving at 14"/min. When confirmed 16 hours later it had already doubled in apparent speed and was about 1 magnitude brighter. Although never brighter than 18th mag, it was followed over the next two nights reaching a speed of over 180"/min during the evening of April 22nd, 5 hours after passing Earth at 1.4 Lunar Distances.

Another NEO Confirmation Page object observed on the evening of April 19th turned out to be an 18th mag comet (later designated C/2007 H2 Skiff), announced the next day by the Minor Planet Center (MPC) on MPEC 2007-H33. The comet was moving north at 3"/min but later, when the images were checked for other moving objects (by stacking for main belt minor planet motion of 0.5"/min in a westerly direction), a minor planet could be seen about 4' north of the comet. The comet passed a mere 23" west of the minor planet at about 23:00 UT that night.

Using Astrometrica and the MPCs Minor Planet Checker web page it could not be matched with a known object, so the next night the unidentified object was picked up again and the details of both nights were sent off to the MPC. The MPC could not ID it with a known object, assigned it provisional designation 2007 HB5 and gave Great Shefford discovery credit for this main belter. This is a good example of making use of the images taken for a different purpose - on the discovery night five other observatories reported positions for C/2007 H2 around the same time as I did, but only one, Juan Lacruz at La Canada (J87) in Spain also reported positions for 2007 HB5 that night.

Friday 6 April 2007

2007 March notes: 2007 EH, 2007 EK and 6R10DB9

March was an exceptional month for NEO close approaches, with ten objects observed moving faster than 25"/min, and two observed while inside the distance of the Moon.

In the table below "/min is the apparent speed of the object in arcsec/minute and LD = Lunar distance = 0.00257 AU

2007 DJ 01.9 30 0.021 8
2007 DX40 02.1 33 0.028 11
2007 EH 11.1 1,250 0.0011 0.4
2007 EK 13.2 382 0.0018 0.7
2007 EV 15.2 42 0.016 6
2007 EO88 18.8 288 0.0032 1.2
2007 FC3 20.8 142 0.0090 3.5
2007 FG1 22.0 25 0.025 10
2007 FY20 31.9 35 0.018 7
2006 VV2 31.9 57 0.024 9

2007 EH is the fastest natural object I have tracked and is currently the third closest observed approach of a designated minor planet ever (only 2004 FH and 2006 DD1 having had astrometry reported while closer).

It was discovered 44 hours before the close approach and put on the NEO Confirmation page during the afternoon of 9th March, but that evening, with it still unconfirmed I spent some time searching about +/- 0.5 degree around the predicted position but without success. Reviewing the discovery positions from the Catalina Sky Survey, one or two looked somewhat out of step with the others and so an orbit was calculated leaving these out. The resulting prediction was about 1 degree west of the NEOCP prediction and the object was indeed picked up close to that place, allowing the subsequent close approach prediction for the next night to be greatly refined.

The close approach itself was remarkable, to watch images appear on the monitor with the object racing across so fast... at it's fastest speed of 1,250"/min it was 15th mag and covering the field of view of my CCD in 53 seconds, or the diameter of the Moon in less than 1.5 minutes! When first picked up on the evening of the 10th at 19:16 UT it was at RA=11h 41m Dec=+30, reached RA=15h 50m Dec=+60 at 00:45UT on 11th and was last seen at 02:22UT at RA=19h 37m Dec=+50, over 80 degrees of sky covered in less than 7 hours!

Full details of the confirmation, animations from the close approach night and details of the techniques used to measure astrometry of such a fast moving object can be found at http://www.birtwhistle.org/Gallery2007EH.htm.

2007 EK which passed at 0.7 Lunar Distances just two nights after 2007 EH would in a more average month have headlined itself. However, it was nearly two magnitudes fainter than 2007 EH and so was not quite the spectacle of the earlier NEO.

One other noteworthy object seen during the month was 6R10DB9, a Catalina Sky Survey temporary designation given to an object discovered last September which has since then been in geocentric orbit, originally expected to be a small piece of man-made space junk, but increasingly suspected of being natural. It was picked up at mag +19 moving at 24"/min in a dense starfield in Gemini, just 1.2 Lunar Distances from Earth, as it approached it's 2nd to last perigee. It will be perturbed out of the Earth's vicinity for the foreseeable future this coming summer. Attempts to obtain spectra with the 6.5-m MMT during the March perigee were unfortunately clouded out, but there will be one last opportunity in June to try and determine once and for all whether it is indeed a natural object. Some details of the story so far of this interesting object can be found at http://www.birtwhistle.org/Gallery6R10DB9.htm, but hopefully more to come in June and July.

Tuesday 6 March 2007

2007 February notes: 2007 BD7, 2007 BZ48 and 2007 DA61

The first half of February was reasonably favourable with 8 nights used up to the 14th and 49 hours logged, while the last half of the month was very poor, with just 4 cloud interrupted hours logged over 3 nights.

Apollo object 2007 BD7 discovered on 23 Jan 2007 from Lowell was followed on four nights up to 6th Feb as it approached Earth, with it's phase angle reaching about 90 degrees on the last night. It was moving swiftly into evening twilight and with the phase angle continuing to increase and magnitude fading rapidly it was not seen again.

Another Apollo 2007 BZ48, discovered by the Mt. Lemmon Survey in January and making a close approach in February, was also observed on four nights, last seen on the morning of the 7th within hours of it passing Earth at 4.5 Lunar distances at a moderately fast 56"/minute.

The only object imaged from the NEO Confirmation Page in the last half of the month was 2007 DA61, during a half hour gap in the clouds on 25th Feb. This turned out to have a perihelion distance of 2.6 AU, in a highly elliptical orbit, elements available by early March giving P=134 years and indicating perihelion at the beginning of March 2007 (though these values may change somewhat as further positions are obtained). It appeared completely stellar in my images and is likely to be a Damocloid asteroid, but it is possible it might show some signs of outgassing with large instruments in the coming weeks.

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.

Sunday 7 January 2007

2006 December notes: Observing statistics

After a very good November, the weather in December was much poorer. Only ten nights were usable with several of those being near the Full Moon. Ten consecutive cloudy nights over the Christmas break was the longest cloudy period at Great Shefford since the start of 2004. 14 objects were observed off the NEO confirmation page, along with another 15 NEOs, all but a couple were observed just on single nights.

Stats for 2006 (2005) show a slight reduction in clear nights from the previous year, but an increase in the number of images taken, due mainly to the upgrading of the CCD in Sep 2005 to allow faster image download times. Images were taken on 169 (181) nights, while the number of hours spent observing was 798 (841). However, 80,515 (69,239) images were taken, with the CCD shutter being open for a total of 507 hours (438 hours) over the year.