12 Oct 2009 SSA-NEO-ESA-HO-019/1.3 Solar System Missions Division (SRE-SM) SSA- NEO Detlef Koschny, Gerhard Drolshagen, Nicolas Bobrinsky European Space Agency, Solar System Missions Division Keplerlaan 1 NL-2201 AZ Noordwijk ZH [email protected]Asteroid occultation primer Predictions How are they observed? Results: Size and shape Results: Positions Conclusions The relevance of asteroid occultation measurements mage courtesy: David A. Hardy
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12 Oct 2009SSA-NEO-ESA-HO-019/1.3Solar System Missions Division (SRE-SM)
SSA-NEO
Detlef Koschny, GerhardDrolshagen, Nicolas Bobrinsky
European Space Agency,Solar System Missions Division
The relevance of asteroid occultation measurements
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12 Oct 2009SSA-NEO-ESA-HO-019/1.3Solar System Missions Division (SRE-SM)
SSA-NEOAsteroid occultation primer
Prediction error because of position uncertainties
12 Oct 2009SSA-NEO-ESA-HO-019/1.3Solar System Missions Division (SRE-SM)
SSA-NEO
These observations are relevant because:• This is the only direct method of determining shape and size of an
object other than going there (optical interferometry was used and published in Feb 2009 – almost direct but not quite, see Delbo 2009, using the VLT/MIDI)
• The main contributing error in the determined astrometric position is the error of the star position in the catalog => milliarcsec accuracy is achievable
12 Oct 2009SSA-NEO-ESA-HO-019/1.3Solar System Missions Division (SRE-SM)
SSA-NEO
Is it useful to include occultation work in our SSA systems?
These observations are relevant because:• This is the only direct method of determining shape and size of an
object other than going there (optical interferometry was used and published in Feb 2009 – almost direct but not quite, see Delbo 2009, using the VLT/MIDI)
• The main contributing error in the determined astrometric position is the error of the star position in the catalog => milliarcsec accuracy is achievable
12 Oct 2009SSA-NEO-ESA-HO-019/1.3Solar System Missions Division (SRE-SM)
SSA-NEOOccultation primer - predictions
Steve Preston’s predictions
Hristo Pavlov’s ‘OccultWatcher’
David Herald’s ‘Occult’
Oliver Klos’ maps
12 Oct 2009SSA-NEO-ESA-HO-019/1.3Solar System Missions Division (SRE-SM)
SSA-NEOHow are they observed?
• Use telescope with video camera to record a video of the star• Ensure high-accurate timing measurements by inserting GPS-
synchronized time into video
12 Oct 2009SSA-NEO-ESA-HO-019/1.3Solar System Missions Division (SRE-SM)
SSA-NEOResulting video
12 Oct 2009SSA-NEO-ESA-HO-019/1.3Solar System Missions Division (SRE-SM)
SSA-NEOStar intensity versus time
12 Oct 2009SSA-NEO-ESA-HO-019/1.3Solar System Missions Division (SRE-SM)
SSA-NEOStar intensity versus time
Occultation
12 Oct 2009SSA-NEO-ESA-HO-019/1.3Solar System Missions Division (SRE-SM)
SSA-NEOResults: Size/shape
• Combining several observations, size and possibly even shape of theasteroid (in the planeof observation) can bedetermined directly
12 Oct 2009SSA-NEO-ESA-HO-019/1.3Solar System Missions Division (SRE-SM)
SSA-NEO
Shape model derived from photometric observations
Occultation observations
12 Oct 2009SSA-NEO-ESA-HO-019/1.3Solar System Missions Division (SRE-SM)
SSA-NEOResults: Positions
• D. Herald (Australia) has set up an interface with the Minor Planet Center to allow submission of positions determined by occultations, using the IAU observatory code 244.
• Accuracies can be obtained to 0.01” down to 0.0002” relative to the star. Star accuracies are about 0.07” (=> Optical astrometry results in ~0.1”)
• When better positions available data can be improved (e.g. using the USNO Robotic Astrometric Telescope, Zacharias et al. 2009; J-MAPS – Gaume + Dorland 2008; Gaia)
12 Oct 2009SSA-NEO-ESA-HO-019/1.3Solar System Missions Division (SRE-SM)
SSA-NEOConclusions - I
• Asteroid occultations (= asteroid occults star) can provide shape and size of asteroids in the plane of observation
• They can provide high-accuracy position measurements– Accuracy limited by accuracy of star in catalogue
• Observation limit is the magnitude of the star (not the asteroid)
• Observations mainly done by amateurs– Pipeline for shape/size: see work by Euraster, E. Frappa– Pipeline for position measurements set up by D. Herald
• BUT: For objects <a few km accuracy issues– Timing accuracy => go to higher frame rate– Star positions => get better star catalogue– Path uncertainty => use more observing stations
12 Oct 2009SSA-NEO-ESA-HO-019/1.3Solar System Missions Division (SRE-SM)
SSA-NEOConclusions - II
Possible improvements• One central system for predictions• One central database for results• Use larger aperture for more events (fainter stars) or just
better signal-to-noise• Organise campaigns for
shape/centroid determinations• Use better cameras,
e.g. EM-CCDs; more dynamics,higher frame rate
• Go space-based – Kepler?
12 Oct 2009SSA-NEO-ESA-HO-019/1.3Solar System Missions Division (SRE-SM)
SSA-NEOConclusions - III
• Yes… but:– 0.02 s timing accuracy needs to be ensured – higher
accuracy preferred (use high-speed cameras)– Good signal-to-noise needed– Enough stations to cover predicted path and still
give reasonable spatial accuracy are needed
Is it useful to include occultation work in our SSA systems?
12 Oct 2009SSA-NEO-ESA-HO-019/1.3Solar System Missions Division (SRE-SM)
SSA-NEOResources
• Steve Preston’s predictions– http://www.asteroidoccultation.com/