SSA-NEO-ESA-HO-019/1.3 Solar System Missions Division (SRE-SM) SSA-NEO 12 Oct 2009 Detlef Koschny, Gerhard Drolshagen, Nicolas Bobrinsky European Space Agency, Solar System Missions Division Keplerlaan 1 NL-2201 AZ Noordwijk ZH Asteroid occultation primer Predictions How are they observed? Results: Size and shape Results: Positions Conclusions The relevance of asteroid occultation measurements Image courtesy: David A. Hardy

SSA-NEO-ESA-HO-019/1.3 Solar System Missions Division (SRE-SM) SSA-NEO 12 Oct 2009 Asteroid occultation primer Prediction error because of position uncertainties

SSA-NEO-ESA-HO-019/1.3 Solar System Missions Division (SRE-SM) SSA-NEO 12 Oct 2009 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-ESA-HO-019/1.3 Solar System Missions Division (SRE-SM) SSA-NEO 12 Oct 2009 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-NEO-ESA-HO-019/1.3 Solar System Missions Division (SRE-SM) SSA-NEO 12 Oct 2009 Occultation primer - predictions Steve Prestons predictions Hristo Pavlovs OccultWatcher David Heralds Occult Oliver Klos maps

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

SSA-NEO-ESA-HO-019/1.3 Solar System Missions Division (SRE-SM) SSA-NEO 12 Oct 2009 Resulting video

SSA-NEO-ESA-HO-019/1.3 Solar System Missions Division (SRE-SM) SSA-NEO 12 Oct 2009 Star intensity versus time

SSA-NEO-ESA-HO-019/1.3 Solar System Missions Division (SRE-SM) SSA-NEO 12 Oct 2009 Star intensity versus time Occultation

SSA-NEO-ESA-HO-019/1.3 Solar System Missions Division (SRE-SM) SSA-NEO 12 Oct 2009 Results: Size/shape Combining several observations, size and possibly even shape of the asteroid (in the plane of observation) can be determined directly

SSA-NEO-ESA-HO-019/1.3 Solar System Missions Division (SRE-SM) SSA-NEO 12 Oct 2009 Shape model derived from photometric observations Occultation observations

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

SSA-NEO-ESA-HO-019/1.3 Solar System Missions Division (SRE-SM) SSA-NEO 12 Oct 2009 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 for shape/centroid determinations Use better cameras, e.g. EM-CCDs; more dynamics, higher frame rate Go space-based – Kepler?

SSA-NEO-ESA-HO-019/1.3 Solar System Missions Division (SRE-SM) SSA-NEO 12 Oct 2009 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?

SSA-NEO-ESA-HO-019/1.3 Solar System Missions Division (SRE-SM) SSA-NEO 12 Oct 2009 Resources Steve Prestons predictions – Occult – occultations.com/iota/occult4.htm occultations.com/iota/occult4.htm OccultWatcher (prediction software) – her.html her.html European Asteroidal Occultation Network – Euraster – results from European occultation observations – Asteroid occultation page by the Czech Astronomical Society (on behalf of the International Occultation Timing Association IOTA – Database of observations by Mike Kretlow – LiMovie – Light Measurement tool for occulations – net.ne.jp/k_miyash/occ02/limovie_en.html net.ne.jp/k_miyash/occ02/limovie_en.html Bruno Sicardys home page – Leslie Youngs home page – Archive of occultations in the Planetary Data System (PDS) – Japanese page on occultations – e/occult-e.html e/occult-e.html Australasian page on occultations – North Americas page on occultations – sults sults