modeling planetary systems around sun-like stars
DESCRIPTION
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. - PowerPoint PPT PresentationTRANSCRIPT
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 HawleyFebruary 23, 2006
AST 591: Journal Club
Scope of Study
Presents five Sun-like stars with characteristics of exo-KBsModels debris disks and discusses implications for our Solar SystemModels one star with emission consistent with photosphere
Outline
Context and IntroductionObservationsSpectral Energy DistributionsDebris Disk ModelingEvolutionary ModelSummary
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 SpitzerMore info: Meyer et al. (2004)
Observations
6 targets, 5 of which have excess (3) emission at 70m but 3 excess at 33 mTaken 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 photometryPredicted 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 ~10-100m
Radiation Pressure and Poynting-Robertson Drag
Particles <~1m have blow out time of <100yrParticles >~1m subject to slow P-R drag, destroyed after 106-107 years– Short compared to age of systems,
implying object are being replenished
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)
HD 8907 - closer look
Used disk model from Wolf & Hillenbrand (2003) and Levenberg-Marquardt algorithm for best-fitAssumptions– n(r)r-1, n(a)a-3.5, amax=1mm, Rout=100AU
Vary parameters: Rin, amin, Mdust
This model gives Rin of 42.5 AU compared to 48 AU of simple blackbody model
Warm Dust Mass
Masses on order of 10-6 M
Age Determination
Age bins rather than specific ages usedInferred from chromospheric and coronal activity– Indicated respectively by CaIIH and K
emission and X-ray luminosity
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
•Results are within factor of 2-3 of predicted 70m excesses for the targets, except HD 13974•Present solar system dust mass 30% of HD 145229
HD 13974 - closer look
Binary system (period=10days)Model would suggest much higher 70m excess than observed– No KB bodies?– Neptune-like planet to perturb and cause
collisions?
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
SummaryFEPS is allowing a more complete database of debris systems5 sources have excess emission at 70m, indicating exo-KBsSED 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 fluxesHD 13974 either doesn’t have KB-like objects or they have been ejected from the systemDust depletion <Rin due to Jupiter-like planet at 10-20 AU