January was rather disappointing with fewer hours logged observing than for the same month in any of the previous 5 years.
A highlight was the recovery of the Apollo 2005 BT1, originally discovered by LINEAR on 16 Jan 2005 and followed for 47 days. Predicted to have a favourable approach in Jan 2008, a search was started from Great Shefford on Jan 24th, the expected magnitude given by the Minor Planet Center was +19.1 and the likely uncertainty area given as over 8 degrees long, aligned almost North-South.
I covered the central 4 degrees with my 18'x18' field of view during 24/25 Jan and extended this to the N by another degree on 26 Jan but searching was cut short by clouds. Only 0.5 degrees was added to the S the next night before clouds interrupted again, but finally on 28 Jan, on the first attempted field that night the NEO was finally caught, 2.35 degrees off track to the south. It had taken 814 images taken on the four nights, of 30 separate fields to locate it.
The next night was cloudy again in the UK so I contacted Sergio Foglia (IAU code 147) and Luca Buzzi (code 204) in Italy to see if either of them had good skies to try and get a confirming second night of positions for it. Sergio was not able to observe but Luca managed to get some astrometry before he too was clouded out. With the positions from 2008 Sergio then searched for possible images from the old SkyMorph image archives and managed to locate it faintly on two images from 07 Jan 2002 taken with the Palomar 1.2-m Schmidt. All three sets of positions were sent off to the MPC and within the hour MPEC 2008-B60 was issued formally announcing the recovery.
Another extensive search that didn't end up with such a positive result was also a LINEAR discovery found at 03h UT on 16 Jan and posted on the NEO Confirmation page with temporary designation BI10604 just after midnight on 17 Jan. Although relatively bright at mag +17, by the time I could observe on the evening of 17 Jan the uncertainty area was a 1 deg x 2.5 deg oval. I covered the whole area with multiple images being taken of 31 different fields, but did not find it. By the end of the 4 hour session the area had already expanded by a further 0.5 degrees. It never did get recovered by any observatory and two nights later was removed from the NEOCP...
A good set of luck came my way on 7th Jan while I was following up on one of the main belt discoveries I had made in December (2007 XS16). I found a very faint moving object, about mag +21, that did not match any known object and so measured positions of it. I had hoped to try for it again in the coming nights and send in two nights of astrometry to the Minor Planet Center, but clouds stopped any further attempt for over a week. By 17th Jan I decided to just send in the positions as a one night stand (ONS), expecting that I would not hear any more about it. However, by the next day the MPC had managed to match it up to a ONS from the 1.5-m reflector of the Mt Lemmon Survey obtained 5 days after mine on 12 Jan. It was designated as 2008 AV72 and I was given discovery credit for having the earlier of the two ONS!
With this extra data I now realised that other images taken of 2007 XS16 from the previous month might include 2008 AV72 and on re-examining these managed to find it on images taken 29 Dec and then 19 Dec 2007. After these pre-discovery positions were sent in, the MPC quickly managed to find various other ONS back to May 2000 and even two occasions where the object had been given a designation on the basis of two nights of observations (not enough to determine a proper orbit), these being 2000 JF4 and 2006 PH11. Because 2008 AV72 had a 2 month observed arc in 2007/8 it was retained as the primary designation and with observations at 5 oppositions and an MPC uncertainty code of 1 it is now in a state where it could potentially get numbered - not bad for just sending in the ONS from 07 Jan having lost hope of being able to find it again!
Monday, 4 February 2008
Sunday, 6 January 2008
2007 December notes: Observing statistics, 2007 XZ9
2007 ended up with some surprising statistics for Great Shefford. Even though we suffered the very bad run of summer weather from May through August I ended up with about 5% more nights used than in 2006, about 5% more time exposing the CCD (22 days 3hours in total) and about 14% more images taken than in the previous year.
The Catalina NEO Survey was snowed out for some of the month, though for the remaining time there were still some fairly busy periods, with several occasions when there were 20, 30 or more newly discovered objects needing follow-up on the NEO Confirmation page. More than 50 new NEOs were eventually added by the surveys to the overall tally by month end, despite the weather.
One consequence of the surveys being out of action for days at a time was a good crop of main belt minor planets available for discovery by amateurs. I picked up 12, my highest monthly total and other amateurs were also very successful too. Most of the NEOs observed here were only picked up for one or two nights, with 2007 XZ9 (an Apollo discovered by LINEAR) being observed the longest, but that only for 6 days.
The Catalina NEO Survey was snowed out for some of the month, though for the remaining time there were still some fairly busy periods, with several occasions when there were 20, 30 or more newly discovered objects needing follow-up on the NEO Confirmation page. More than 50 new NEOs were eventually added by the surveys to the overall tally by month end, despite the weather.
One consequence of the surveys being out of action for days at a time was a good crop of main belt minor planets available for discovery by amateurs. I picked up 12, my highest monthly total and other amateurs were also very successful too. Most of the NEOs observed here were only picked up for one or two nights, with 2007 XZ9 (an Apollo discovered by LINEAR) being observed the longest, but that only for 6 days.
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.
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!
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.
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.
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.
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| 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.
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