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Modeling Planetary Systems Around Sun-like Stars

Modeling Planetary Systems Around Sun-like Stars. Paper: Formation and Evolution of Planetary Systems: Cold Outer Disks Associated with Sun-like Stars, Kim, J.S., et al. 2005, ApJ 632, 659. Wendy Hawley February 23, 2006 AST 591: Journal Club. Scope of Study.

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Modeling Planetary Systems Around Sun-like Stars

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  1. Modeling Planetary SystemsAround Sun-like Stars Paper: Formation and Evolution of Planetary Systems: Cold Outer Disks Associated with Sun-like Stars, Kim, J.S., et al. 2005, ApJ 632, 659. Wendy Hawley February 23, 2006 AST 591: Journal Club

  2. Scope of Study • Presents five Sun-like stars with characteristics of exo-KBs • Models debris disks and discusses implications for our Solar System • Models one star with emission consistent with photosphere

  3. Outline • Context and Introduction • Observations • Spectral Energy Distributions • Debris Disk Modeling • Evolutionary Model • Summary

  4. Context • Previous Work: • Meyer et al. (2004) : debris disk around Sun-like stars • Cohen et al. (2003): data analysis with Kurucz model • Wolf & Hillenbrand (2003): dust disk models

  5. Introduction • Why study other planetary systems? • Puts our Solar System in context • Debris systems in our Solar System • Asteroid belt (2-4 AU) - zodiacal dust cloud • Kuiper Belt (30-50 AU) - beyond Neptune • Other systems can be used to help model ours

  6. Spitzer Space Telescope • Data taken from FEPS (Formation and Evolution of Planetary Systems) • Previous studies done using Infrared Astronomical Satellite (IRAS) and Infrared Space Observatory (ISO) • Detection of new systems with Spitzer • More info: Meyer et al. (2004)

  7. Observations • 6 targets, 5 of which have excess (3) emission at 70m but 3 excess at 33 m • Taken using MIPS (Multiband Imaging Photometer for Spitzer) at 24 and 70 m bands

  8. Spectral Energy Distributions • Expected photospheric emission found using Kurucz model on published photometry • Predicted magnitudes found using method outlined in Cohen et al. (2003)

  9. Debris Disk Models • Assumptions: • Optically thin disk in thermal equilibrium • Temperature depends on distance from star • Max. Temp. ~100 K, Min. Equilibrium Distance 10 AU for grains of radius ~10-100m

  10. Radiation Pressure and Poynting-Robertson Drag • Particles <~1m have blow out time of <100yr • Particles >~1m subject to slow P-R drag, destroyed after 106-107 years • Short compared to age of systems, implying object are being replenished

  11. Simple Blackbody Grain Models • Based on Tc (excess color temperature) •  calculated from Planck formula • Ax : emitted grain cross-sectional area • Grain luminosity • Grain mass • Rin found from formula used by Backman and Paresce (1993)

  12. HD 8907 - closer look • Used disk model from Wolf & Hillenbrand (2003) and Levenberg-Marquardt algorithm for best-fit • Assumptions • n(r)r-1, n(a)a-3.5, amax=1mm, Rout=100AU • Vary parameters: Rin, amin, Mdust

  13. This model gives Rin of 42.5 AU compared to 48 AU of simple blackbody model

  14. Warm Dust Mass • Masses on order of 10-6 M

  15. Age Determination • Age bins rather than specific ages used • Inferred from chromospheric and coronal activity • Indicated respectively by CaIIH and K emission and X-ray luminosity

  16. Solar System Evolutionary Model • Model from Backman et al. (2005) • Assumptions: • Rin=40 AU, Rout=50 AU • Starting mass of KB 10 M • P-R induced “zodiacal” dust cloud extending inward

  17. Results are within factor of 2-3 of predicted 70m excesses for the targets, except HD 13974 • Present solar system dust mass 30% of HD 145229

  18. HD 13974 - closer look • Binary system (period=10days) • Model would suggest much higher 70m excess than observed • No KB bodies? • Neptune-like planet to perturb and cause collisions?

  19. Possible Planets? • Dust depletion occurring inside Rin • Sublimation and grain “blowout” ruled out • Planet preventing P-R drift • Planet would be >Mjupiter and have a semimajor axis of 10-20 AU, plus exterior belt of planetesimals • More work to be done through direct imaging and constraints on low-mass companions

  20. Summary • FEPS is allowing a more complete database of debris systems • 5 sources have excess emission at 70m, indicating exo-KBs • SED modeling indicated log(LIR/L*)-5.2, color temperatures 55 to 58 K, Rin 18 to 46 AU • Solar system model within a few factors of observed fluxes • HD 13974 either doesn’t have KB-like objects or they have been ejected from the system • Dust depletion <Rin due to Jupiter-like planet at 10-20 AU

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