Tidal Circularization in the Open Cluster NGC 6819

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Tidal Circularization in the Open Cluster NGC
6819

• Sylvana Yelda
• Advisor Robert Mathieu

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Tidal Circularization

• Orbits constantly change
• Earth-Moon
• Hot Jupiters

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NGC 6819

• WIYN Open Cluster Study (WOCS)
• Very concentrated, rich cluster
• solar metallicity
• Intermediate age 2.4 Gyr
• 300 pc above Galactic plane
• Cygnus

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Hole et al. 2005
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Searching for Binaries

• Radial velocity
• Member rvNGC68192.17 km s-1
• Candidate binary rms gt 2.0 km s-1
• Spectroscopic binaries
• Cross-correlation
• function

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Searching for Binaries

• SB1 vs. SB2

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Orbital Solutions
Periastron
Apastron
Apastron
http//astrosun2.astro.cornell.edu/academics/cours
es//astro201/bin_orbits.htm
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P21.285 e0.445 0.036
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P3340.983 e0.723 0.055
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P25.537 e0.021 0.019
Longest period circular orbit
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P1.847 e0.022 0.022
a0.03 AU!
Shortest period circular orbit
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P4.850 e0.016 0.008
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Angular Momentum

• Conserved
• Rotational ? Orbital
• Star rotates slower
• Eccentricity decreases
• Lorbital ? corresponds to e ? (circular)

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Tidal Forces

• Tidal Force 1/d3
• Misalignment of tidal bulges w.r.t. line joining
  centers produces torque
• Rotational angular momentum transferred to
  orbital (tdL/dt)
• Transition from eccentric to circular
• Closest binaries ? Circular orbits
• Distant binaries ? Nonzero eccentricities

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Tidal Circularization Period

• Period at which typical binary (e0.35) has
  circularized in the age of population

Meibom Mathieu 2005
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n39
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Summary

• Short-period ? Circular
• Longer-period ? Non-zero eccentricities
• CP of NGC6819 consistent with observed trend
• With increasing age, longer period binaries
  become circularized

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Thank you!Robert MathieuSoeren MeibomAaron
GellerTabetha HoleElla BradenEd
MierkiewiczREU StudentsUW Faculty Staff