Physical Characterization of the Vesta Family Asteroids

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Physical Characterization of the Vesta Family
Asteroids
William H. Ryan Eileen V. Ryan (New Mexico
Tech/MRO)
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Project Overview

• Multi-apparition Photometric study of Vesta
  family (asteroids dynamically and chemically
  linked to Vesta).
• Motivation To understand the Vesta family
  formation from a cratering impact event.
  Observational data is being acquired to ascertain
  whether family members are re-accumulated rubble
  piles or intact, ejected spall fragments.
• Family Members observed
• 34 Asteroids Observed
• 22 Periods Derived
• 10 Studied in detail (multi-apparition
  light-curves and/or at multiple solar phase
  angles)
• Facilities used 1.8 m VATT (VORG) UH 2.2m, 1m
  CTIO (NOAO) 0.35 m Etscorn MRO 2.4-meter.

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1933 Tinchen June 1999
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3703 Volkonskaya June 1999
1929 Kollaa March 2004
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1933 Tinchen Nov 2003 (0.35-meter)
Additional V-asteroid data using sub-meter class
telescopes published by Brian Warner and Russ
Durkee
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3155 Lee January 2000
Also March 2004 May 2005 data under analysis
(plus published data from November 2002, B.
Warner). Unusual more difficult to interpret.
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3155 Lee March 2004
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3782 Celle 5 January 2003
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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)
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Celle Follow-up October 2005
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3703 Volkonskaya December 2000
Another binary (periodicity 24hrs), but needed
more data to reliably model the system.
Spectral Class V-type (R. Binzel, private
communication)
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3703 Volkonskaya

• Events observed, but still unable to acquire
  complete coverage of the 2 occultation events.
• Additional Volkonskaya data thanks to
• Fumi Yoshida (NAOJ) and Bisei Obs Staff
• Shigeru Takahashi (Lulin)
• Mansur Ibrahimov (Maidanak)
• Richard Crowe, S. Stewart, D. Terry (UH)

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Confirmation 3703 Volkonskaya is a Binary!

• Finally a robust confirmation (7 nights)
  of periodic attenuations for 3703 Volkonskaya
  in May 2006 at CTIO 1-meter telescope.
• Size Ratio 0.38 - 0.47
• Periodicity 24 hr
• (Potential orbital periods of 24 hr or
  48 hr) .

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Current Status

• Confirm orbital period of Volkonskaya system!
• Refine/identify orbital models of Celle and
  Volkonskaya binary systems
• Additional photometry of field stars from
  previous runs in order to determine more precise
  H values
• Data analysis Phase relations, H-values, and
  shape characteristics