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Synthetic Lightcurve Signatures of Unresolved Objects: A Comparison with Observations

Synthetic Lightcurve Signatures of Unresolved Objects: A Comparison with Observations. Eileen V. Ryan, William H. Ryan, Ruth Juarez (NM Tech/Magdalena Ridge Observatory), Carlos Martinez (UNM), Lou Blackwell (AFRL). Asteroid/Satellite Photometry.

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Synthetic Lightcurve Signatures of Unresolved Objects: A Comparison with Observations

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  1. Synthetic Lightcurve Signatures of Unresolved Objects: A Comparison with Observations Eileen V. Ryan, William H. Ryan, Ruth Juarez (NM Tech/Magdalena Ridge Observatory), Carlos Martinez (UNM), Lou Blackwell (AFRL) 2005 AMOS Technical Conference

  2. Asteroid/Satellite Photometry • Asteroids/satellites shine from reflected sunlight-- prop. to cross-sectional area at small solar phase angles (0 is sun behind observer). • As the object rotates, the amount of light varies. • By measuring the light variation over time, we derive a rotation rateand constrain orientation & shape. • Triaxial ellipsoid model works for large number of asteroids (Drummond et al. 1988; Michalowski et al. 1990; etc.) • Objective: Extend triaxial model to more complex shapes for irregular asteroids & satellites. Asteroid Ida (Rotation Images, Galileo Spacecraft) 2005 AMOS Technical Conference

  3. “Typical” Asteroid Lightcurve Doubly periodic behavior– two minima & maxima per cycle. Ryan et al. 2004 Temporal Visible/IR asteroid data. Ryan et al. 2004 2005 AMOS Technical Conference

  4. Model Lightcurve Asteroid Kleopatra Origin for doubly periodic behavior– reproduced even by irregular shapes. 2005 AMOS Technical Conference

  5. Triaxial Ellipsoid Model (Aspect=) Lightcurve amplitude is dependent on viewing geometry (Aspect=): Maximum at Aspect= 90 and minimum at Aspect= 0 (looking along the rotation axis). Ellipsoid’s axial dimensions: (a, b, c) 2005 AMOS Technical Conference

  6. Amplitude Decreases with Aspect Angle 2005 AMOS Technical Conference

  7. Triaxial Ellipsoid Model (Aspect= ):Observed Amplitude and Magnitude H(0) = absolute magnitude 2005 AMOS Technical Conference

  8. Aspect Angle Determined by Observer Geometry Observing targets at various viewing geometries hopefully will allow us to cover a broad range of aspect angles to properly fit the model parameters. 2005 AMOS Technical Conference

  9. Generalized Inverse Problem This method allows you to fit A and H as a function of rotation axis position and the object’s shape parameters. 2005 AMOS Technical Conference

  10. Inverse Problem Solution 2005 AMOS Technical Conference

  11. Asteroid 16 Psyche Test Case: Resulting Fit Triaxial ellipsoid model has historically been an effective approach for basic shape studies. Parameters of fit: 2005 AMOS Technical Conference

  12. More Complex Lightcurve: 3155 Lee NASA-funded work (Vesta Family): This is what prompted us to consider the crossover to satellite studies– same solution for complex objects is needed. Ryan et al. 2000 2005 AMOS Technical Conference

  13. IDL Demo for Lee (possibility): 2005 AMOS Technical Conference

  14. 3782 Celle: 5 January 2003 Ryan et al. 2004 2005 AMOS Technical Conference

  15. January 2003 (Residuals): Binary Secondary/Primary diameters = 0.43  0.01 Primary Diameter ~ 6 km (H ~ 12.5) Primary Rotational Period = 3.84 hours Orbital Period = 36.57  0.03 hours Mean density = 2.2  0.4 g/cm3 (Basalt ~ 2.9 g/cm3) (Ryan, Ryan & Martinez 2004) 2005 AMOS Technical Conference

  16. Challenges Extending this work to Artificial Satellites: • Complex shapes and surface properties • Coupled rotational and solar phase angles, especially for LEO’s • Observational Challenges • Trailed images for rapid rotators (low signal) • Tracking challenges for LEO’s 2005 AMOS Technical Conference

  17. Current Telescope: 0.35-meter Meade • Used for Satellite characterization studies. • Also used for student training & ground- based observations of Deep Impact. Deep Impact Before After (0.5 magnitude brightening) 2005 AMOS Technical Conference

  18. Meade 0.35-meter Data: NORAD 08840 Rocket body in geosynchronous transfer orbit: Tracking at sidereal rates and letting the rocket body trail. Ryan et al. 2005 2005 AMOS Technical Conference

  19. Composite Lightcurve Peaks are very sharp--not diffuse scattering surface like asteroid lightcurves; a more mirror-like surface. Ryan et al. 2005 2005 AMOS Technical Conference

  20. Work in Progress • Continued observations of different objects (extend to LEO’s). • Continued development of Direct Model (different surface characteristics, complex shapes, etc.). • Collaborations to develop generalized inverse model. • Bigger telescope!!! (next slide) 2005 AMOS Technical Conference

  21. Future Facility: MRO 2.4-meter Telescope Scale Model See poster: The Magdalena Ridge Observatory 2.4-meter Telescope (Gordon Pentland, EOS Technologies) First Light: September 2006 2005 AMOS Technical Conference

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