Synthetic Lightcurve Signatures of Unresolved Objects: A Comparison with Observations
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2005 AMOS Technical Conference
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
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 rate and 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
“Typical” Asteroid Lightcurve
Temporal Visible/IR asteroid data.
Ryan et al. 2004
Ryan et al. 2004
Doubly periodic behavior– two minima & maxima per cycle.
2005 AMOS Technical Conference
Model Lightcurve
Asteroid Kleopatra
Origin for doubly periodic behavior– reproduced even by irregular shapes.
2005 AMOS Technical Conference
Triaxial Ellipsoid Model (Aspect=)
Lightcurve amplitude isdependent 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
Amplitude Decreases with Aspect Angle
2005 AMOS Technical Conference
Triaxial Ellipsoid Model (Aspect= ):Observed Amplitude and Magnitude
H(0) = absolute magnitude
2005 AMOS Technical Conference
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
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
Inverse Problem Solution
2005 AMOS Technical Conference
Asteroid 16 Psyche Test Case: Resulting Fit
Parameters of fit:
Triaxial ellipsoid model has historically been an effective approach for basic shape studies.
2005 AMOS Technical Conference
More Complex Lightcurve: 3155 Lee
Ryan et al. 2000
NASA-funded work (Vesta Family): This is what prompted us to consider the crossover to satellite studies– same solution for complex objects is needed.
2005 AMOS Technical Conference
IDL Demo for Lee (possibility):
2005 AMOS Technical Conference
3782 Celle: 5 January 2003
Ryan et al. 2004
2005 AMOS Technical Conference
January 2003 (Residuals): Binary
Secondary/Primary diameters = 0.43 0.01Primary Diameter ~ 6 km (H ~ 12.5)Primary Rotational Period = 3.84 hoursOrbital Period = 36.57 0.03 hours
(Ryan, Ryan & Martinez 2004)
Mean density = 2.2 0.4 g/cm3 (Basalt ~ 2.9 g/cm3)
2005 AMOS Technical Conference
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
Current Telescope: 0.35-meter Meade
• Used for Satellite characterization studies.
• Also used for student training & ground- based observations of Deep Impact.
Before After (0.5 magnitude brightening)
Deep Impact
2005 AMOS Technical Conference
Meade 0.35-meter Data: NORAD 08840
Ryan et al. 2005
Rocket body in geosynchronous transfer orbit:
Tracking at sidereal rates and letting the rocket body trail.
2005 AMOS Technical Conference
Composite Lightcurve
Ryan et al. 2005
Peaks are very sharp--not diffuse scattering surface like asteroid lightcurves; a more mirror-like surface.
2005 AMOS Technical Conference
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
Future Facility: MRO 2.4-meter Telescope
Scale Model
First Light: September 2006See poster:The Magdalena Ridge Observatory 2.4-meter Telescope (Gordon Pentland, EOS Technologies)
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