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Observing Asteroid Occultations

Observing Asteroid Occultations. Steve Preston September 24, 2013 stevepr@acm.org. Typical Asteroid Occultations. Asteroid size: 10km diameter and larger – usually 30km to 100km. Duration of occultation: typically a few seconds but can last minutes in some rare cases.

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Observing Asteroid Occultations

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  1. ObservingAsteroid Occultations Steve Preston September 24, 2013 stevepr@acm.org

  2. Typical Asteroid Occultations • Asteroid size: 10km diameter and larger – usually 30km to 100km. • Duration of occultation: typically a few seconds but can last minutes in some rare cases. • Star magnitudes: Occultations of naked-eye stars are very rare. Most occultations involve stars that are mag 11 or dimmer.

  3. 2004 Dec 23 (402) Chloe

  4. Why Observe Asteroid Occultations? • Fun • Challenging • Dim stars, equipment • Mobile setups (possibly more than one) • Explore new technology – video, CCD, data reduction • Science • Verify asteroid size/shape • VERY accurate position for asteroid relative to star • Detection of double stars • Detection of asteroid satellites

  5. IOTAInternational Occultation Timing Association • Education • Awareness • Observing Techniques • Predictions • Observations • Coordination • Collect • Publish

  6. IOTA Collaborations • International Occultation Groups • IOTA • IOTA/ES (Europe) • RASNZ (Australia/New Zealand) • JOIN (Japan) • IOTA/ME (Middle East)

  7. IOTA Collaborations • Professional astronomers • IAU Minor Planet Center • USNO (US Naval Observatory) • IMCEE (France) • SwRI • MIT

  8. IOTA RESULTS • IOTA observes about 200 events per year worldwide. • Primarily North America, Europe, Japan, Australia • Over 1300 observed events in occultation database. • 35+ double star observations. • Over 1200 positions reported to the MPC

  9. 2001 Sep 07 (9) Metis

  10. 2011 Jul 19 (90) Antiope • 58 Observations • 41 positive • Mostly mobile • Many unattended • Observers scattered from California to Alberta • Antiope is a double asteroid with both components about 90km in diameter

  11. Which events to observe? • Observing Asteroid Occultations = Game of chance • Formal uncertainty in star positions usually fall between 10mas and 30mas. • Formal uncertainty in asteroid position ranges from 10mas to 100+mas. • Main belt asteroids are usually 30 to 50mas in diameter. • The formal uncertainty in locating the path of the asteroid’s shadow is usually a significant fraction of the path width and often several times the path width. • Observe often and prioritize events with good statistics and/or lots of observers. • Events within three sigma are possible.

  12. www.asteroidoccultation.com

  13. Event Details Page

  14. Event Map

  15. OccultWatcher Program • Lists events passing near your location • Give locations of observers planning to observe an event • You can announce your own plan to observe • Links to “classic” path plot for each event • Google Map of path

  16. Where to Observe… • Observing from Home • Convenient • Good choice for low probability events • Good choice if it helps fill in the “gaps” in coverage from other observers

  17. Where to Observe… • Remote observing • Improves chances of positive event • More challenging • Finding good location • Equipment setup and backup • Weather • More time and expense

  18. How to Observe… • Goal • Monitor the star during the predicted time of the event (including uncertainty in the time of the event). • If you see an event, accurately record the times of any disappearance or reappearance of the star. • If you don’t see an event, record the times during which you monitored the star.

  19. How to Observe… • General Tips • Aperture – There are more events with dimmer stars. So more aperture is better. • All times are UT (subtract 6 hrs to convert to MDT, 7 hrs to convert to MST). • Find the star well ahead of time. Practicing days ahead of time is a good idea. • Reporting results • Report forms on IOTA website • Report any positive events • Report negative events if any positives from group

  20. How to Observe… • Methodologies • Visual • Video Recording • Multiple Stations • CCD Drift Scan

  21. Observing Visually • Timing • WWV (5mhz, 10mhz, or 15mhz) • Record audio with your voice (audio tape recorder, cell phone, etc..) • Allow plenty of time to find the star • Avoid eye fatigue – don’t stare for a long time. • Call out short phrase for events: ”mark”

  22. Observing with Video • Cameras • PC164CEX-2 camera ($139 from Supercircuits) • 8” SCT with f/3.3 focal reducer reaches mag 11 stars • Orion ST 80mm – about mag 10 • Watec 120N+ ($750) • Can go several mag fainter with longer exposures (up to 4 seconds) • Adapter: “C” to 1 ¼” (Knight Owl and others) • Focal reducer • Almost always increases magnitude reach significantly. • Knight Owl 0.5x focal reducer ($30) & C mount adapter ($16)

  23. Observing with video • Video recording • Camcorders work well – particularly for remote stations • Standard VCR is fine for recording. • Timing • WWV: Record WWV Receivers on audio track • PA-3 pre-amp mike from Supercircuits works well. • GPS Time inserters • Convenient for data reduction • IOTA-VTI (www.videotimers.com) $250 • When using video time insertion, record WWV on audio track as backup

  24. Video Setup for Occultations

  25. Multiple Stations… • More stations => greater odds of success • When possible I setup one station at home and setup another remote station. • Techniques: • “Helper” to monitor tracking and start recording • “Unattended” with pre-point and timer recording

  26. Pre-Pointing • Goal: point telescope to location in sky of star at the time of the event and let star drift across at the right time. • How: choose star that will pass close to the right location well ahead of the event time. • Field of View must be large enough for event duration and uncertainty in time. • Be sure that telescope is stable (watch for settling, wind, etc.) • Use Apparent RA and adjust for sidereal vs UT rate. • “Occult” software will generate list of stars with pre-point times.

  27. Observing with CCD drift scan • Let star drift across CCD during exposure • Accurate UT timing is tricky … Most CCD cameras do not provide accurate sync between UT and start of exposure. • John Broughton’s tips: • http://www.asteroidoccultation.com/observations/DriftScan/Index.htm

  28. IOTA Resources • IOTA (International Occultation Timing Association) • http://lunar-occultations.com/iota/iotandx.htm (main IOTA site) • http://tech.groups.yahoo.com/group/IOTAoccultations/ (Yahoo group) • Asteroid Occultation Observing and Reporting: • http://www.asteroidoccultation.com/observations/ • OccultWatcher • http://www.hristopavlov.net/OccultWatcher/ • Asteroid Occultation predictions and other info • http://www.asteroidoccultation.com/

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