Planet Formation and DetectionEstimating fpPlanet FormationSMM image of VegaJACH, Holland et al.SMM image of Vega shows dust peaksoff center from star (*). Fits a modelwith a Neptune like planet clearing agap. Can test by looking for motion ofclumps in debris disk.Model by Wyatt (2003), ApJ, 598, 1321Disks versus Age of StarEvidence for CollisionsBinary Stars• About 2/3 of all stars are in binaries– Most common separation is 10-100 AU• Can binary stars have disks?– Yes, but binary tends to clear a gap– Disks well inside binary orbit– Or well outside binary orbitBrown Dwarfs• Stars range from 0.07 to ~100 Msun• Jupiter is about 0.001 Msun• Brown dwarfs between stars and planets– Dividing line is somewhat arbitrary– Usual choice is 13 Mjupiter– Brown dwarfs rarely seen as companions to stars– But “free-floaters” as common as stars– Many young BDs have disks• Planets around BDs?Planet DetectionMethods and ResultsCan We See Them?• Not yet, but there are plans…• Problem is separating planet light from starlight– Star is 109 times brighter in visible light– “Only” 106 times brighter in infraredPlanet is Much Fainter than StarIndirect DetectionWobbling starDetect effect of planet on star (both orbit around center of mass)M1M2M1M2M1M2M =1M2M >>1 M 2Large planet will make a star “wobble”In plane of sky observeposition shiftAlong our line ofsightObserve DopplerShiftStar and Planet Orbit Center of Mass1 mas-1 masThe Sun as viewed from 10 pc (~30 ly)The Astrometric TechniqueMeasure stellar position (angle) accurately - see wobble compared to moredistant starsHow far does the star wobble?M*R*Center of massMplrR =*M rplM*We measure angle; for small angles,Θ =R*DΘ =M rplM*in radiansR*ΘDsorDBig planet, big orbitsmall star, close to sunCurrent limit: 1 mas = 10-3 arcsec = 2.8 × 10-6 degrees = 4.9 × 10-8 radianse.g. M = M , M = M , D = 15 ly ⇒ Θ = 1 maspl Jupiter*30 lyThe Spectroscopic TechniqueMeasure velocity, not position, of starUse spectrometer to get Doppler Shift ofspectral lineshiftλlightM rV ∝Mpl**1/2 1/2Shift ∝Big planet, small orbitSmall starDistance doesn’t matter (except for brightness)Edge - OnThe Doppler ShiftLight is a wavewavelength(λ)moving starwavelength seen bywavelength seen byBLUESHIFTREDSHIFTλ observedλ emitted= 1 + vcDoppler Shift Magnitude and direction of velocityBut only along line-of-sight30 lyWhat We Can Learn1. There is a planet(If not a mistake)2. The orbital period (P)(The time for pattern to repeat)3. The orbital radius r3 ∝ M* P2(Kepler’s Third Law)4. Lower limit to planet mass (M )Conservation of momentumplMpl>M V P**2π r= if we see orbit edge-on> if tiltedComparison of Search MethodsAstrometricBig PlanetBig OrbitSmall StarNearby StarSpectroscopicBig PlanetSmall OrbitSmall Star--Edge-on OrbitAdvantagesOther MethodsTransits: Planet passes in front of a starstartransitLightfromstarTimeusOnly about 0.5% of stars withplanets will line upFirst planet found with this method in January 2003; 5 detected as ofJanuary 2005Microlensing: Light from more distant star is focused by gravity of nearer star passing infrontusnearer stardistant starplanetplanetlightfromdistantstarFortuitous alignment ⇒ brightensOne planet found this way as of January 2005Planets from the Transit MethodOGLE-TR-10Light curveStar field, shows starPlanet Detected by Microlensing OGLE 2003-BLG-235/MOA 2003-BLG-53Sharp spikes indicate second lens.Mass of second lens only 0.4% asmassive as star. Companion is verylikely a planet.Future ProspectsDirect detection (and study) of Earth-like planets~ 2015 Terrestrial Planet Finder (TPF)Darwin (Europe)Astrometric Method GAIA ~ 2010MJ Planets out to 600 ly.Further Spectroscopic SearchesTransits Kepler (~ 2007)Monitor 100,000 stars for 4 years“Hundreds of Terrestrial Planets”Artist’s conception of the view from the outmost planet of three in UpsilonAndromedaeCopyright Lynette Cookused with permissionhttp://www.extrasolar.spaceart.orgCopyright Lynette Cookused with permissionhttp://www.extrasolar.spaceart.orgArtist’s conception of Transit of HD209458Copyright Lynette Cookused with permissionhttp://www.extrasolar.spaceart.orgArtist’s conception of 47 U ma “view” from Moon of the Second PlanetImplications of New PlanetsPlanets more massive than Jupiter can form around stars like the Sun.Large Planets can form much closer to a star than Jupiter (or move there)Does this mean we are unusual and our ideas about other planetarysystems are just “solar system chauvinism”?Not necessarily.The ones found so far are the “easy” ones. (Big planets close to a star)Now there are many more with lower masses than higher massesToo early to say that we are unusual.Astrometric Technique (1 mas)M (in Jupiter Masses)pl0.10.31310301000.010.1110100Spectroscopic Technique (50 - 100 m s-1)(at ~ 15 ly)JupiterSaturnSeparate StarsStarsOrbital Radius (AU)Successful Doppler planet search programs:ELODIE/CORALIE (H.P./La Silla) Mayor, Queloz, Udry, et al. (North/South)Hamilton/HIRES (Lick/Keck) Marcy, Butler, Fischer, et al. (North)Cs23 (McDonald 2.7m) Cochran, Hatzes (North)AFOE (Whipple) Noyes, Brown, et al. (North)ESO CES (La Silla) Kurster, Hatzes, Endl, et al. (South)UCLES (AAT) Butler, Tinney, et al. (South)- with about 80 extrasolar planet candidates identified:- more than 1000 stars examined.Direct Detection in Future• Terrestrial Planet Finder (TPF)/Darwin– TPF-C Visible light coronagraph (~2014)– TPF-I Infrared interferometer (~2020)• Goal is to detect earth-mass planets• And to see what gases in atmosphere– Suitable for life?• http://planetquest.jpl.nasa.gov/TPF/tpf_index.htmlTPF ConceptsTPF-C Visible light coronagraph (2014)TPF-I Infrared Interferometer (2020)Spectroscopy of atmosphereBrown DwarfsBetween stars and planets:M < 0.07 M cannot fuse hydrogen substellarM > 0.013 M ~ 13 Mjup (This boundary is still argued about)~Emit infrared and cool slowly as they release gravitational potential energyVery few are found as stellar companionsBut they appear to be common as “free-floaters”May have their own planets ??Implications:1. Stars and planets form in different ways (no intermediate masses in orbit)2. There could be free-floating planets3. Brown dwarfs might have planets (bigger f - but suitable for
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