The relevance of asteroid occultation measurements
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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

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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


The relevance of asteroid occultation measurements

  • 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


The relevance of asteroid occultation measurements

  • 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


Resulting video

Resulting video


Star intensity versus time

Star intensity versus time


Star intensity versus time1

Star intensity versus time

Occultation


Results size shape

Results: Size/shape

  • Combining several observations, size and possibly even shape of theasteroid (in the planeof observation) can bedetermined directly


The relevance of asteroid occultation measurements

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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