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Tidal Circularization in the Open Cluster NGC 6819

Tidal Circularization in the Open Cluster NGC 6819. Sylvana Yelda Advisor: Robert Mathieu. Tidal Circularization. Orbits constantly change Earth-Moon Hot Jupiters. NGC 6819. WIYN Open Cluster Study (WOCS) Very concentrated, rich cluster ~ solar metallicity Intermediate age: ~ 2.4 Gyr

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Tidal Circularization in the Open Cluster NGC 6819

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  1. Tidal Circularization in the Open Cluster NGC 6819 Sylvana Yelda Advisor: Robert Mathieu

  2. Tidal Circularization • Orbits constantly change • Earth-Moon • Hot Jupiters

  3. NGC 6819 • WIYN Open Cluster Study (WOCS) • Very concentrated, rich cluster • ~solar metallicity • Intermediate age: ~2.4 Gyr • ~300 pc above Galactic plane • Cygnus

  4. Hole et al. 2005

  5. Searching for Binaries • Radial velocity • Member: rvNGC6819=2.17 km s-1 • Candidate binary: rms > 2.0 km s-1 • Spectroscopic binaries • Cross-correlation function

  6. Searching for Binaries • SB1 vs. SB2

  7. Orbital Solutions Periastron Apastron Apastron http://astrosun2.astro.cornell.edu/academics/courses//astro201/bin_orbits.htm

  8. P=21.285 e=0.445 ± 0.036

  9. P=3340.983 e=0.723 ± 0.055

  10. P=25.537 e=0.021 ± 0.019 *Longest period circular orbit

  11. P=1.847 e=0.022 ± 0.022 a~0.03 AU! *Shortest period circular orbit

  12. P=4.850 e=0.016 ± 0.008

  13. Angular Momentum • Conserved • Rotational → Orbital • Star rotates slower • Eccentricity decreases • Lorbital↑ corresponds to e ↓ (circular)

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

  15. Tidal Circularization Period • Period at which typical binary (e~0.35) has circularized in the age of population Meibom & Mathieu 2005

  16. n=39

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

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

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