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Understanding the extrasolar planetary systems : observations & theories

Understanding the extrasolar planetary systems : observations & theories of disks and planets Pawel Artymowicz U of Toronto 1. Beta Pictoris and other dusty disks in planetary systems 2. Planet formation: are there really still two scenarios?

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Understanding the extrasolar planetary systems : observations & theories

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  1. Understanding the extrasolar planetary systems: observations & theories of disks and planets Pawel Artymowicz U of Toronto 1. Beta Pictoris and other dusty disks in planetary systems 2. Planet formation: are there really still two scenarios? 3. Discovery of the first 160+ planetary systems 4. Migration type I-III 5. Origin of structure in the dust and gas disks How to find this talk online: either google up “pawel”, or get directly planets.utsc.utoronto.ca/~pawel/UofA.ppt

  2. Astrophysics of planetary systems Astrophysics of Stars and Planets 1980s: little overlap in planetary sciences atmosph. Stellar Astrophysics Dynamics incl. Hydrodynamics and statics materials Gen.Rel. radioisotopes Radiation transfer Geo- chem High energ physics. Thermodynamics of gas meteoritics Nuclear physics Disk theory IDPs & zodiacal disk Astronomy:observations of circumstellar disks

  3. Astrophysics of planetary systems Astrophysics of Planets in 2000s: unification of disciplines atmosph. Stellar Astrophysics Dynamics, hydrodynamics and hydrostatics materials Gen.Rel. radioisotopes IDPs, zodiacal light disks Radiation transfer Disk theory Geo- chem High ener. physics. Thermodynamics of gas meteoritics Nuclear physics Astronomy:observations of circumstellar disks, radial velocity exoplanets

  4. First milestone in search for planetary systems was detection of dust around normal stars : Vega phenomenon Chemistry/mineralogy/crystallinity of dust Astrochemical unity of nature

  5. Infrared excess stars (Vega phenomenon)

  6. Beta Pictoris thermal radiation imaging (10 um) Lagage & Pantin (1993)

  7. 1984 1993 Beta Pictoris, visible scattered starlight comparison with IR data yields a high albedo, A~0.4-0.5 (like Saturn’s rings but very much unlike the black particles of cometary crust or Uranus’ rings).

  8. Small dust is observed due to its large total area Parent bodies like these (asteroids, comets) are the ultimate sources of the dust, but remain invisible in images due to their small combined area Comet

  9. Optical thickness: perpendicular to the disk in the equatorial plane (percentage of starlight scattered and absorbed, as seen by the outside observer looking at the disk edge-on, aproximately like we look through the beta Pictoris disk)

  10. What is the optical thickness ? It is the fraction of the disk surface covered by dust: here I this example it’s about 2e-1 (20%) - the disk is optically thin ( = transparent, since it blocks only 20% of light) picture of a small portion of the disk seen from above Examples: beta Pic disk at r=100 AU opt.thickness~3e-3 disk around Vega opt.thickness~1e-4 zodiacal light disk (IDPs) solar system ~1e-7

  11. STIS/Hubble imaging (Heap et al 2000) Modeling (Artymowicz,unpubl.): parametric, axisymmetric disk cometary dust phase function Vertical optical thickness  Vertical profile of dust density Radius r [AU] Height z [AU]

  12. Dust processing: collisions 1. Collisional time formula 2. The analogy with the early solar system (in the region of today’s TNOs = trans-Neptunian objects, or in other words, Kuiper belt objects, KBOs; these are asteroid-sized bodies up to several hundred km radius)

  13. Time between collisions (collisional lifetime) of a typical meteoroid. Obviously, inversly proportional to the optical thickness (doubling the optical depth results in 2-times shorter particle lifetime, because the rate of collision doubles). P = orbital period, depends on radius as in Kepler’s III law. This formula is written with a numerical coefficion of 1/8 so as to reproduce the fact that a disk made of equal-sized particles needs to have the optical thickness of about 1/4 to make every particle traversing it vertically collide with some disk particle, on average. The vertical piercing of the disk is done every one-half period, because particles are on inclined orbits and do indeed cross the disk nearly vertically, if on circular orbits. If the orbits are elliptic, a better approximate formula has a coefficient of 12 replacing 8 in the above equation.

  14. How does the Vega-phenomenon relate to our Solar System (Kuiper belt, or TNOs - transneptunian objects)

  15. Evidence of planetesimals and planets in the vicinity of beta Pictoris: 1. Lack of dust near the star (r<30AU) 2. Spectroscopy => Falling Evaporating Bodies 3. Something large (a planet) needed to perturb FEBs so they approach the star gradually. 4. The disk is warped somewhat, like a rim of cowboy hat, which requires the gravitational pull of a planet on an orbit inclined by a few degrees to the plane of the disk. 5. Large reservoir of parent (unseen) bodies of dust needed, of order 100 Earth masses of rock/ice. Otherwise the dust would disappear quickly, on the collisional time scale

  16. This is how disks look a decade later - much better quality data, fewer artifacts, disks appear smoother.

  17. HST/WFPC2 camera a fantastic large-scale view of beta Pictoris out to r ~800 AU

  18. B Pic b(?) sky? Beta Pictoris Evidence of large bodies (planetesimals, comets?) 11 micron image analysis converting observed flux to dust area (Lagage & Pantin 1994)

  19. FEB = Falling Evaporating Bodies hypothesis in Beta Pictoris FEB star absorption line(s) that move on the time scale of days as the FEBs cross the line of sight H & K calcium absorption lines are located in the center of a stellar rotation-broadened line

  20. Microstructure of circumstellar disks: identical with IDPs (interplanetary dust particles) mostly Fe+Mg silicates (Mg,Fe)SiO3 (Mg,Fe)2SiO4

  21. A rock is a rock is a rock… which one is from the Earth? Mars? Beta Pic? It’s hard to tell from remote spectroscopy or even by looking under a microscope!

  22. EQUILIBRIUM COOLING SEQUENCE Chemical unity of nature… and it’s thanks to stellar nucleosynthesis! Silicates silicates T(K) What minerals will precipitate from a solar-composition, cooling gas? Mainly Mg/Fe-rich silicates and water ice. Planets are made of precisely these things. ices

  23. Crystallinity of minerals Recently, for the first time observations showed the difference in the degree of crystallinity of minerals in the inner vs. the outer disk parts. This was done by comparing IR spectra obtained with single dish telescopes with those obtained while combining several such telescopes into an interferometric array (this technique, long practiced by radio astronomers, allows us to achieve very good, low-angular resolution, observations). In the following 2 slides, you will see some “inner” and “outer” disk spectra - notice the differences, telling us about the different structure of materials: amorphous silicates = typical dust grains precipitating from gas, for instance in the interstellar medium, no regular crystal structure crystalline grains= same chemical composition, but forming a regular crystal structure, thought to be derived from amorphous grains by some heating (annealing) effect at temperatures up to ~1000 K.

  24. ~90% amorphous ~60% amorphous ~45% amorphous compare Beta Pic, ~95% crystalline

  25. That was good, but people wanted PLANETS Direct imaging Transits Structures in dusty disks (footprints in the sand) Indirect but almost direct: periodic, Keplerian red+blueshifts in stellar spectra, or timing of pulsars

  26. Pulsar planets: PSR 1257+12 B 2 Earth-mass planets and one Moon-sizes one found around a millisecond pulsar First extrasolar planets discovered by Alex Wolszczan [pron.:Volshchan] in 1991, announced 1992, confirmed 1994 Name: PSR 1257+12 A PSR 1257+12 B PSR 1257+12 C M.sin 0.020 ± 0.002 ME 4.3 ± 0.2 ME 3.9 ± 0.2 ME Semi-major axis: 0.19 AU 0.36 AU 0.46 AU P(days): 25.262±0.003, 66.5419± 0.0001, 98.2114±0.0002 Eccentricity: 0.0 0.0186 ± 0.0002 0.0252 ± 0.0002 Omega (deg): 0.0 250.4 ± 6 108.3 ± 5 The pulsar timing is so exact, observers now suspect having detected a comet!

  27. Pulsar planets: PSR 1257+12 B 2 Earth-mass planets and one Moon-sizes one found around a millisecond pulsar First extrasolar planets discovered by Alex Wolszczan [pron.:Volshchan] in 1991, announced 1992, confirmed 1994 +comets ?? A B C m: 0.020 ME 4.3 ME 3.9 ME a: 0.19 AU 0.36 AU 0.46AU e: 0 0.0186 0.0252 O: 0.0 250.4 108.3

  28. Radial-velocity planets around normal stars

  29. -450: Extrasolar systems predicted (Leukippos, Demokritos). Formation in disks -325 Disproved by Aristoteles 1983: First dusty disks in exoplanetary systems discovered by IRAS 1992: First exoplanets found around a millisecond pulsar (Wolszczan & Dale) 1995: Radial Velocity Planets were found around normal, nearby stars, via the Doppler spectroscopy of the host starlight, starting with Mayor & Queloz, continuing wth Marcy & Butler, et al.

  30. Orbital radii + masses of the extrasolar planets (picture from 2003) Radial migration Hot jupiters These planets were found via Doppler spectroscopy of the host’s starlight. Precision of measurement: ~3 m/s

  31. Like us? NOT REALLY

  32. Marcy and Butler (2003)

  33. 2005 ~2003

  34. m sin i vs. a Zones of avoidance? multiple single

  35. m sin i vs. a Zones of avoidance? Result: a----m

  36. Eccentricity of exoplanets vs. a and m sini a e ? m a e ? m m, a, esomewhat correlated: a e ? m

  37. Eccentricity of exoplanets vs. a and m sini a e ? m a e ? m m, a, esomewhat correlated: a e ? m

  38. Gravitational Instability and the Giant Gaseous Protoplanet hypothesis

  39. Gravitational stability requirements Local stability of disk, spiral waves may grow Local linear instability of waves, clumps form, but their further evolution depends on equation of state of the gas.

  40. From: Laughlin & Bodenheimer (2001) Disk in this SPH simulation initially had Q ~ 1.5 > 1 The m-armed global spiral modes of the form grow and compete with each other. But the waves in a stable Q~2 disk stop growing and do not form small objects (GGPs).

  41. Recently, Alan Boss revived the half-abandoned idea of disk fragmentation Clumps forming in a gravitationally unstable disk (Q < 1) GGPs?

  42. Two examples of formally unstable disks not willing to form objects immediately Durisen et al. (2003) Break-up of the disk depends on the equation of state of the gas, and the treatment of boundary conditions.

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