The relevance of asteroid occultation measurements

1. 12 Oct 2009 The relevance of asteroid occultation measurements

2. 12 Oct 2009 Asteroid occultation primer

3. 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

4. 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

5. 12 Oct 2009 Occultation primer - predictions

6. 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

7. 12 Oct 2009 Resulting video

8. 12 Oct 2009 Star intensity versus time

9. 12 Oct 2009 Star intensity versus time

10. 12 Oct 2009 Results: Size/shape Combining several observations, size and possibly even shape of theasteroid (in the planeof observation) can bedetermined directly

11. 12 Oct 2009

12. 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 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)

13. 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

14. 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 forshape/centroid determinations Use better cameras,e.g. EM-CCDs; more dynamics,higher frame rate Go space-based � Kepler?

15. 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

16. 12 Oct 2009 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