Observational Windows on the Dynamics of Open Clusters

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Observational Windowsonthe Dynamics of Open
Clusters

• Robert D. Mathieu
• University of Wisconsin - Madison

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Typical Open Cluster M 300 Mo Rc 1 pc Rt
20 pc s 0.3 km s-1 rc 10 Mo pc-3
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WIYN Open Cluster Study

• Comprehensive and definitive photometric,
  astrometric, and spectroscopic databases for new
  fundamental open clusters.
• A body of investigations which address critical
  astrophysical problems through study of open
  clusters.

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WOCS Senior Scientists

• C. Deliyannis Indiana photometry, spectroscopy,
  abundances
• P. Demarque Yale theoretical stellar evolution
• T. Girard Yale astrometry, proper motions
• K. Honeycutt Indiana photometric monitoring,
  compact binaries
• R. Mathieu Wisconsin radial velocities, binary
  populations
• I. Platais JHU astrometry, proper motions,
  photometry
• A. Sarajedini Florida photometry, stellar
  evolution
• W. van Altena Yale astrometry, proper motions
• T. von Hippel Texas photometry, luminosity
  functions

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WOCS Clusters

Log Age (Gyrs)
First Generation
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WOCS Strategy

• Imaging/Photometry
• Deep UBVRI images of cluster cores
• UBVRI wide-field surveys to tidal radii
• Photometric monitoring for variability
• Astrometry
• Precise stellar positions
• Deep, wide-field proper motions
• Spectroscopy
• Abundance determinations
• Metallicity, CNO, and lithium
• Precise radial velocities
• Projected rotation velocities
• Stellar activity

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NGC 188 1840 pc E(B-V) 0.04 7 Gyr Fe/H
-0.12 1000 Mo (d 85o)
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Photometry Precision 0.012 mag
(BVRI) 0.03 mag (U) Accuracy
0.02 mag (BVRI)
Sarajedini et al. 1999 WOCS II
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Photometry
Von Hippel et al. 1999 WOCS I
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Proper Motions 0.15 mas yr-1 Positions 0.2
mas 7812 objects V21 0.75 deg2
Platais et al. 2004 WOCS XVII
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(No Transcript)
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Radial Velocities 0.4 km s-1 500 VR/night V lt
16.5 0.75 deg2 (WIYN 3.5m)
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VR
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93 spectroscopic binaries 55 orbital solutions P
lt 3000d
Mathieu et al. 2004 WOCS XVIII
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Outcomes for Stellar Dynamics

• Superb 3-dimensional membership determination
• for entire evolved cluster population to beyond
  tidal radius
• Reliable 2-dimensional membership determination
• to 0.5 Mo and beyond tidal radius
• Photometric mass function to 0.1 Mo in cluster
  core
• Complete census of short-period, solar-type
  binary population,
• with orbital elements

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The Interface of Two Classical FieldsStellar
Astrophysics and Stellar Dynamics
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M67 4.5 Gyr Fe/H -0.04 1000 Mo
1.3 Mo
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Binary Frequency
Spectroscopic Binaries
For P lt 1000d M67 19 4 Field 16 3
Mathieu, Latham Griffin 1990 Mathieu et
al. 2004
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Mathieu et al. 2003
S1063 P18.4 d e 0.21 g 34.3 km/s pm 97
S1113 P2.8 d e 0 g 33.4 km/s pm 98
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Tidal Circularization Rates
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NGC 188 7 Gyr Pcutoff 14.9 days
Mathieu et al. 2004
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Meibom Mathieu 2004
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Opening Thoughtson Choice of Open Cluster(s)
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WOCS Clusters

Log Age (Gyrs)
First Generation
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Optimal Cluster Properties (with an
observational bias)

• Rich several thousand members to 0.1 Mo
• evolution without complete evaporation
• meaningful statistics
• Old age greater than 1 Gyr
• multiple relaxation times
• solar-mass evolution
• Nearby d lt 2 kpc
• accessible main-sequence binary population
• Accessible -20o lt d lt 20o
• observable from both hemispheres
• Out of Plane b gt 10o
• minimize field-star contamination, especially at
  Rt