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- Peter Birtwhistle
- Great Shefford Observatory
- www.birtwhistle.org
- Summer Meeting, Basingstoke
- 19th July 2008
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- Minor Planets & the Near Earth Objects (NEOs)
- Equipment
- Basic techniques
- Positional work – Astrometry
- Photometry
- Discovery
- Very fast moving objects (VFMOs)
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- Ideally…
- 25cm / 10” or bigger telescope
- CCD (essential for real-time work)
- GoTo mount and some degree of automation in telescope positioning and
image taking
- ‘Ready to go’ (permanently polar-aligned mount)
- … Images need to be measured and results sent to the Minor Planet Center
(MPC) the same night
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- Example: 2004 TD18 21/22 October 2004
- 120 x 30s exposures = 1 hour total exposure
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- New discoveries from NEO Confirmation Page (NEOCP)
- Unconfirmed, with potentially large uncertainties
- Follow-up of confirmed discoveries
- NEOs during their discovery apparition
- NEOs at their second return
- Recovery , with potentially large uncertainties – line of variation
- Follow-up after recovery
- NEOs at further returns
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- Example: AO18761
- discovered by LINEAR 2004 May 24 05:00 UT at mag +18.8, motion 34”/min
- Added to NEOCP 14 hours later at 18:48 UT
- By 2004 21:00 UT mag +19.3 motion 24”/min
- Prediction by the Minor Planet Center showing area of sky where object
is likely to be
- Position (0,0) is the ‘nominal’ position, the most
likely location to find the object.
- Each dot represents a ‘variant’ orbit.
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- Discovered by LINEAR 06:58 UT 11 July 2005
- Added to the NEOCP 40 hours later(!)
- Magnitude 16-17 and moving at 50”/min
- By then uncertainty area 9° x 0.3° and growing fast
- Telescope/CCD field of view 18’x18’ – a big search required…
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- Uncertainties in old orbits mainly in T (Perihelion time)
- 2005 BT1
- 2007 DA
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- This naming collectively honors Ivan O. Yarkovsky, John A. O'Keefe, V.
V. Radzievskij and Stephen J. Paddack, who were instrumental to the
realization that radiation torques due to sunlight can affect the spin
states of minor planets. Data on this object provided the first direct
observational evidence for the YORP effect.
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- Discovered by LINEAR on 11 May 2008 at magnitude +17 and moving
South-East at 46"/min in the evening sky in Virgo, about midway
between Arcturus and Spica…
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- 79 x 6 second exposures taken over a period of 13 min 43 sec
- 4 complete rotations
- Amplitude 0.7 magnitudes
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- Problems for small telescopes discovering faint NEOs …and it needs
plenty of luck to discover a bright NEO…
- Main belt “discoveries” have often been observed before…
- Tying up possibly many one-nighters
- Follow-up at other oppositions to get numbered
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- Normally very small, only bright enough to be discovered when already
close to Earth
- Often very little lead time before closest approach
- Watch NEOCP for telltale signs – fast acceleration within 24 hours
- Try to catch as early as possible on night of close approach –
uncertainties grow quickly
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- VFMOs find you, you don’t find them!
- When to chase and when to ignore?
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- VFMOs find you, you don’t find them…
- When to chase and when to ignore?
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- Must notice in real-time
- Reduce exposure length and shift telescope to keep up for first few
minutes or longer if possible
- Measure positions, preferably not ends of trails
- Use Sat_ID for quick ID of known ART SATs
- Use FindOrb to work out orbit (or simple extrapolation) and extend
ephemeris to keep following…
- Try to determine if artificial satellite or NEO?!
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- Peter Birtwhistle
- Great Shefford Observatory
- www.birtwhistle.org
- Summer Meeting, Basingstoke
- 19th July 2008
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