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 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

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

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

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

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)

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

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

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 ~  m

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 years –Short compared to age of systems, implying object are being replenished

Simple Blackbody Grain Models Based on T c (excess color temperature)  calculated from Planck formula –A x : emitted grain cross-sectional area –Grain luminosity –Grain mass R in found from formula used by Backman and Paresce (1993)

HD 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, a max =1mm, R out =100AU Vary parameters: R in, a min, M dust

This model gives R in of 42.5 AU compared to 48 AU of simple blackbody model

Warm Dust Mass Masses on order of M 

Age Determination Age bins rather than specific ages used Inferred from chromospheric and coronal activity –Indicated respectively by Ca II H and K emission and X-ray luminosity

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

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

HD 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?

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

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(L IR /L * )  -5.2, color temperatures 55 to 58 K, R in 18 to 46 AU Solar system model within a few factors of observed fluxes HD either doesn’t have KB-like objects or they have been ejected from the system Dust depletion <R in due to Jupiter-like planet at AU