SSA-NEO-ESA-HO-019/1.3 Solar System Missions Division (SRE-SM) SSA-NEO 12 Oct 2009 Detlef Koschny,...

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

Keplerlaan 1NL-2201 AZ Noordwijk ZH

[email protected]

Asteroid occultation primerPredictions

How are they observed?Results: Size and shape

Results: PositionsConclusions

The relevance of asteroid occultation measurements

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SSA-NEOAsteroid occultation primer

Prediction error because of position uncertainties


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


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


SSA-NEOOccultation primer - predictions

Steve Preston’s predictions

Hristo Pavlov’s ‘OccultWatcher’

David Herald’s ‘Occult’

Oliver Klos’ maps


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


SSA-NEOResulting video


SSA-NEOStar intensity versus time


SSA-NEOStar intensity versus time

Occultation


SSA-NEOResults: Size/shape

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


SSA-NEO

Shape model derived from photometric observations

Occultation observations


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)


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


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?


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?


SSA-NEOResources

• Steve Preston’s predictions– http://www.asteroidoccultation.com/

• Occult– http://www.lunar-occultations.com/iota/occult4.ht

m

• OccultWatcher (prediction software)– http://hristopavlov.net/OccultWatcher/OccultWatc

her.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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