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The relevance of asteroid occultation measurements. 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?

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the relevance of asteroid occultation measurements
The relevance of asteroid occultation measurements

Detlef Koschny, GerhardDrolshagen, Nicolas Bobrinsky

European Space Agency,Solar System Missions DivisionKeplerlaan 1NL-2201 AZ Noordwijk ZH

[email protected]

Asteroid occultation primerPredictionsHow are they observed?

Results: Size and shapeResults: PositionsConclusions

Image courtesy: David A. Hardy

asteroid occultation primer
Asteroid occultation primer

Prediction error because of position uncertainties

slide3
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
slide4
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

Is it useful to include occultation work in our SSA systems?

occultation primer predictions
Occultation primer - predictions

Steve Preston’s predictions

Hristo Pavlov’s ‘OccultWatcher’

David Herald’s ‘Occult’

Oliver Klos’ maps

how are they observed
How 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
results size shape
Results: Size/shape
  • Combining several observations, size and possibly even shape of theasteroid (in the planeof observation) can bedetermined directly
slide11

Occultation observations

Shape model derived from photometric observations

results positions
Results: 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)
conclusions i
Conclusions - 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
conclusions ii
Conclusions - 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 forshape/centroid determinations
    • Use better cameras,e.g. EM-CCDs; more dynamics,higher frame rate
    • Go space-based – Kepler?
conclusions iii
Conclusions - 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?

resources
Resources
  • Steve Preston’s predictions
    • http://www.asteroidoccultation.com/
  • Occult
    • http://www.lunar-occultations.com/iota/occult4.htm
  • OccultWatcher (prediction software)
    • http://hristopavlov.net/OccultWatcher/OccultWatcher.html
  • European Asteroidal Occultation Network
    • http://www.astrosurf.com/eaon/
  • Euraster – results from European occultation observations
    • http://www.euraster.net/
  • Asteroid occultation page by the Czech Astronomical Society (on behalf of the International Occultation Timing Association IOTA
    • http://mpocc.astro.cz/
  • Database of observations by Mike Kretlow
    • http://sky-lab.net/?Solar_System_-_Occultations
  • LiMovie – Light Measurement tool for occulations
    • http://www005.upp.so-net.ne.jp/k_miyash/occ02/limovie_en.html
  • Bruno Sicardy’s home page
    • http://www.lesia.obspm.fr/perso/bruno-sicardy/
  • Leslie Young’s home page
    • http://www.boulder.swri.edu/~layoung/occl/
  • Archive of occultations in the Planetary Data System (PDS)
    • http://www.psi.edu/pds/resource/occ.html
  • Japanese page on occultations
    • http://uchukan.satsumasendai.jp/data/occult-e/occult-e.html
  • Australasian page on occultations
    • http://occsec.wellington.net.nz/
  • North America’s page on occultations
    • http://www.asteroidoccultation.com/observations/Results
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