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A Tale of Star and Planet Formation Lynne Hillenbrand Caltech Vermeer’s The Astronomer (1688) Mauna Kea (last week) photos by: Sarah Anderson and Bill Bates Context: Our Sun • The Sun is a completely average star. – typical weight – middle age SOHO satellite Context: The stars • At first consideration it might seem as though the Sun and other stars are constant and unchanging. • However, stars are born, they live, and they die. • Many are forming today throughout the Milky Way (3 MSun per year). 2MASS Star formation in galaxies Milky Way galaxy M51 galaxy (central region) HST The Solar Neighborhood Warm interstellar gas (low density) Cold gas clouds (dense) Young clusters Ionized gas (HII region) from massive star winds & supernovae [Huff & Frisch] 450 pc 1500 Lt yrs Where do Stars Form? Molecular gas ( CSO ) Optical image ( HST ) Light comes in different “Wavelengths” slide courtesy of A. Goodman Astronomical dust Wavelength vs Particle Size “Dust Grain” “Dust Grain” Light is “Extincted”; Does not Reach Us Light Goes Right by; Reaches Us Scatterer Light “Scatters” Blue: 3.6 μm Green: 4.5 μm Red: 8.0 μm slide courtesy of T. Megeath Perseus-Taurus-Orion optical photograph (star light) mid-infrared (dust emission) Orion in visible and infrared light Zooming in on Orion Akira Fujii David Malin HST image Bob O’Dell “Nebula” is created by reflected light from hot, massive stars Keck Studies of Newborn Stars • imaging photometry • spectroscopy Slesnick, Hillenbrand, Carpenter MWC 1080 M1 M3 B0 K1 M2 M4 K7 Where do stars form? • Cold clouds of atoms, gas molecules, and dust having masses a few hundred to a few million times the mass of the Sun. factor of 1 million in density factor of 1 million in density Compress yet another factor of 1 million x 1 million to get a star! How do Stars Form? 80,000 AU and 250,000 years Why do stars form? Local Star Formation [North American / Pelican Nebulae] 2MASS Stars Tend to Form in Groups, not Alone Aggregates (unbound) • 10’s of stars • 0.4 - 1.6 lightyear radius • <100 stars / unit volume Clusters (may be bound) • 100’s to 1000’s of stars • 1.6 - 16 lightyear radius • 1000 - 100,000 stars / volume 2MASS 1 parsec is the distance at which Earth would appear 1” away from the Sun (about 3.3 light years) Note that the distance to our nearest neighboring star Centauri is ~1.3 pc Binary Stars Our Sun is a single star, but half of all Sun-like stars are found to be in multiple systems (twins, triplets, quads). Models of star formation have trouble predicting exactly how these systems are made. We are using Keck to observe young binary systems as they form. These studies are difficult because binary stars are typically very close together in projection and because atmospheric distortions blur our observations. Keck can observe these stars because of a technology called Adaptive Optics. AO corrects the atmospheric distortions that normally limit the resolution of telescopes. In typical 0.8” astronomical seeing, a telescope on Mauna Kea can separate the two headlights of a car on Haleakala. Keck + AO could do this for a car in Los Angeles! Adaptive Optics without AO 0.80” seeing (FWHM) with AO FWHM=0.09” • Eliminates atmospheric turbulence; • Allows high-contrast imaging (106). Binary star HD 18940 with the Palomar AO system Very young binary systems look very similar to the old stars that are our nearest neighbors. This means binaries probably form this way, V410 X-ray3 instead of being influenced by close encounters with other stars in their cluster/family. HST (0.8 um) 0.05” 7 AU vs Keck (1.6 um) “diffraction limit” = wavelength ------------------------telescope diameter IZ-072 How Do Young Stars Form? The cloud contracts, and collapses to create a protostar. Leftover gas and dust flattens into a disk. A significant amount of this gas and dust spirals into the star (“accretion”). Some dust in the disk can collide and stick together (“grain growth”). Eventually, pebbles, asteroids, and rocky planets as well as giant planet cores can form. Star and planet formation 10 105 yr Disk/wind Lstar 104 yr Planet building 107 yr 109 yr 1 Planetary system 100 AU Main sequ ence 8,000 5,000 Cloud collapse 2,000 Tstar (K) [Beckwith & Sargent 1996] With Keck we are studying: • • • • • • • Young stellar populations (how big? how old?) Clustering and multiplicity (families) Outflow of material in winds and jets Accretion of material onto forming stars Geometry of circumstellar disks Dissipation of disks and planet formation Discovery of planets around more mature stars Collaborators on Keck work: Scattered light from Protostars Protostellar Outflows • Remove angular momentum • Generate turbulence in molecular cloud Evidence for Outflows Edwards et al 06 “Blue side” absorption in He I at 1.083 μm: broad = stellar wind (seen in strong accretors) narrow = disk wind (seen in weak accretors) [Matt & Pudritz 2005] Evidence for Accretion accreting young stars normal young stars The Inner Accretion Disk • Origin of outflows. • Nature of accretion flows that shock and heat photosphere. [Hartmann 1998] • How big are the indirectly inferred inner disk gaps? Interferometry • Direct imaging is limited by the “diffraction limit” or (wavelength/diameter). This is 0.013-0.045” for a 10m telescope operating in optical/near-infrared. requires AO • We can be even more clever! gets to 0.0048” slide courtesy of J. Eisner Lambda Building Planets from the Raw Materials in Circumstellar Disks • Dust evolution: – growth from interstellar medium sized dust to larger solids: μm cm km moon/Mars sized “oligarchs” 1-10 Mearth planets • Gas dissipation: • • • • accretion on to star outflow in winds/jets irradiation formation of planets [animation by Jeff Alu] How do Planets Form? Formation of Other Solar Systems • “Proto-planetary” disks – Exist around all stars younger than a few million years (<1/1000 Sun’s age) – Disappear on time scales of less than 10 million years • Need to turn dust and gas into planets before the disk disappears! The view from a newborn planet History of Exo-Solar System Planet Detection Planets now suspected to orbit ~8-15% of solar type stars in the solar neighborhood, with many multiple planet systems known. Planetary Masses from Keck RVs TrES-2 TrES-1 1.28 MJup 0.75 MJup TrES-3 1.92 MJup TrES-4 0.84 MJup Search for Exoplanets using Transits TrES-2 Photometry Bright Star Dark Planet 2 r rp p F = = 1% R RJup 2 RSun R 2