Transcript Bob Mathieu (Wisconsin) – Observations of Open Clusters

Observational Windows
on
the Dynamics of Open Clusters
Robert D. Mathieu
University of Wisconsin - Madison
“Typical”
Open Cluster
M = 300 Mo
Rc = 1 pc
Rt = 20 pc
s = 0.3 km s-1
rc = 10 Mo pc-3
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.
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
[Fe/H]
WOCS Clusters
Log Age (Gyrs)
First Generation
Second Generation
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
NGC 188
1840 pc
E(B-V) = 0.04
7 Gyr
[Fe/H] = -0.12
≈ 1000 Mo
(d = +85o)
Photometry
Precision ≈ 0.012 mag (BVRI)
≈ 0.03 mag (U)
Accuracy ≈ 0.02 mag (BVRI)
Sarajedini et al. 1999;
WOCS II
Photometry
Von Hippel et al. 1999;
WOCS I
Proper Motions
0.15 mas yr-1
Positions
0.2 mas
7812 objects
V=21
0.75 deg2
Platais et al. 2004;
WOCS XVII
Radial Velocities
0.4 km s-1
500 VR/night
V < 16.5
0.75 deg2
(WIYN 3.5m)
VR
Mathieu et al. 2004;
WOCS XVIII
93 spectroscopic binaries
55 orbital solutions
P < 3000d
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
The Interface of Two Classical Fields:
Stellar Astrophysics
and
Stellar Dynamics
M67
4.5 Gyr
[Fe/H] = -0.04
≈ 1000 Mo
1.3 Mo
Binary Frequency
Spectroscopic
Binaries
For P < 1000d
M67 19% ± 4
Field 16% ± 3
Mathieu, Latham &
Griffin 1990
Mathieu et al. 2004
Mathieu et al. 2003
S1113
P=2.8 d
e=0
g = 33.4 km/s
pm = 98%
S1063
P=18.4 d
e = 0.21
g = 34.3 km/s
pm = 97%
Tidal Circularization Rates
NGC 188
Mathieu et al. 2004
7 Gyr Pcutoff = 14.9 days
Zahn & Bouchet 1989
Witte & Savonije 2002
Claret & Cunha 1997
(Zahn 1977)
Meibom & Mathieu
2004
Opening Thoughts
on Choice of Open Cluster(s)
[Fe/H]
WOCS Clusters
Log Age (Gyrs)
First Generation
Second Generation
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 < 2 kpc
• accessible main-sequence binary population
• Accessible -20o < d < +20o
• observable from both hemispheres
• Out of Plane | b | > 10o
• minimize field-star contamination, especially at Rt