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What can X-rays tell us about planet formation? Eric Feigelson (Penn State)

What can X-rays tell us about planet formation? Eric Feigelson (Penn State). Hydrodynamical simulation of Jovian planet formation in a disk around a T Tauri star. Our knowledge of planet formation has recently grown in many ways. Protoplanetary disks: Gas & ice (mol spec & comets)

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What can X-rays tell us about planet formation? Eric Feigelson (Penn State)

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  1. What can X-rays tell usabout planet formation?Eric Feigelson (Penn State) Hydrodynamical simulation of Jovian planet formation in a disk around a T Tauri star

  2. Our knowledge of planet formation has recently grown in many ways • Protoplanetary disks: Gas & ice (mol spec & comets) Dust (IR photom & spec, vis silhouette, meteorites) Larger solids (meteorites, beta Pic comets) • Planetary systems: Dynamics from ~110 extrasolar Doppler planets Hot Jovian planet properties from transits • Planetary imagery: None yet, though possible today for nearby young Jovians • Theoretical modeling of the above observations

  3. X-ray effects on protoplanetary disks • While protoplanetary disks are far too cool to emit X-rays, • high energy studies may provide crucial indirectinsights • into planet formation: • Young stellar X-rays will ionize the disks, inducing MHD turbulence which affects Jovian planet formation & migration • Magnetic flaring in young stars may help explain two enigmas in meteoritic studies:the production of short-lived isotopes in disk solids via spallation, and the flash melting of chondrules or CAIs. • X-rays will change disk chemistry & heating • 4. X-ray selected older PMS starsprovide important samples to measure the distribution of disk longevities

  4. High energy processes & protoplanetary disks Mag field lines Cosmic rays Flare X-rays Proto-Jupiter Proto-Earth Flare MeV particles Dead zone Ionized MHD turbulent zone Feigelson IAU Symp 219 2003

  5. 1. X-ray ionization of protoplanetary disks • X-rays from magnetic reconnection events will penetrate • to surprising depths into the disk. Ionizing radiation incident • on a cold disk produces an outer MHD-turbulent layer via the • magneto-rotational instability. The inner midplane remains a • neutral laminar `dead zone’. • Conductivity, ambipolar diffusion, and dynamos will affect the • extent of the turbulent zone. Cosmic ray ionization is also • important. The balance between X-ray and cosmic ray • ionization depends on: Lx & spectrum, X-ray flare geometry, • penetration of low-E cosmic rays in cloud, and recombination • rate within the disk. • Gammie 1996, Glassgold et al. 1997, Igea & Glassgold 1999 • Fromang et al. 2002, Blackman & Tan 2003, Salmeron & Wardle 2003 • Matsumura & Pudritz 2003 • Review: • Glassgold, Feigelson & Montmerle in Protostars & Planets IV 2000

  6. Dead zone calculations for cosmic ray and X-ray ionization in disks with different viscosities. Here, only ~1 keV X-rays are used, not the more energetic X-rays seen with Chandra. Matsumura & Pudritz 2003

  7. Turbulent disk structures produce random walkrather than rapid inward migration Competition between standard planet-disk torques (which produce rapid Type I inward migration) and torques from turbulent density structures. Turbulence randomizes migration, and may accelerate or inhibit planetary growth. Papaloizou et al. 2003; Laughlin et al. 2003; Winters et al. 2003; Rice & Armitage 2003; Menou & Goodman 2004

  8. Dead zone may be active Magnetic field is restricted to outer layers, |z/H|>0.4 Reynolds stress which causes MHD turbulence also avoids inner dead zone But Maxwell stress (vertical motions) induced by non-axisymmetric density waves from the outer zone are present in dead zone 2 z/H -2 Time (tens of orbits) 3-D MHD calculation Fleming & Stone 2003

  9. Turbulent disks may exhibit periodic accretion episodes When central temperature of dead zone exceeds T~800K, ionization may rise to support MHD turbulence. This would produce a burst of accretion. Are these FU Orionis outbursts? Armitage, Livio & Pringle 2001

  10. 2a. A Solar System enigma: Why do the most ancient solid materials of the solar nebula show evidence of MeV irradiation? Excess short-lived radionuclides in carbonaceous chondrite calcium-aluminum inclusions (CAIs) Allende meteorite Isotope t (Myr) Abund 10Be/Be 2.6 9x10-4 26Al/Al 1.1 5x10-5 41Ca/Ca 0.1 1x10-8 53Mn/Mn 5.3 4x10-5 … … … Possibly 7Be (t = 53 days) CAIs Chondrules Lee et al. 1998 McKeegan et al. 2000

  11. Explanations for short-lived isotopes • Injection of recently synthesized stellar material: AGB red giant winds, Wolf-Rayet winds, or supernova remnnant Cameron & Truran 1977, Wasserburg et al. 1994, Arnould et al. 1997 • Spallogenic nuclear reactions by MeV particles impacting the solar nebula Hoyle et al. 1962, Clayton et al. 1977, Feigelson 1982, Shu et al. 1997, Lee et al. 1998 Local spallation also explains spallogenic 21Ne in some free-floating grainsCaffee et al. 1987, Woolum & Hohenberg 1993, Rao et al. 1997 ******************************* Chandra measurements of X-ray flare rates in Orion Nebula solar analogs directly support the local spallation origin of meteoritic isotopic anomalies Feigelson et al. 2002 (see also Feigelson 1982)

  12. 2b. Another Solar System enigma: What melted meteoritic chondrules? The causes of the flash melting of meteoritic chondrules and CAIs has been a major problem for >100 years. Meteoritic literature appears surprisingly unaware of X-ray/radio flare findings. Feigelson 1982, Feigelson & Montmerle 1999 Shu et al. (1997, 2001) develop a (controversial) model for flash melting of CAIs by X-ray from magnetic flares.

  13. X-irradiation should drive non-equilibrium ion-molecular chemistry in disk Dead zone Reynolds number Calculation of chemical reactions and physical state of various layers of an X-irradiated disk Semanov, Weibe, Henning 2004 (also Aikawa & Herbst 2001)

  14. 4. Longevities of protoplanetary disks Astronomical studies of older (5-20 Myr) disks can elucidate longevities of the gaseous, dusty and planetisimal disk phases. Particularly important for Jovian planet formation. Major obstacle is the lack of large, disk-unbiased samples of older PMS stars. Disk signatures are weak and stars have dispersed far from clouds. Feigelson 1996 Review: Hillenbrand 2001 These older PMS stars are mostly found via their X-ray emission. We are pursuing a Chandra snapshot survey to find nearby examples of older PMS stars. Feigelson, Lawson & Garmire 2003

  15. The h Cha cluster JHKL photometry shows inner disks around 2/3 of stars and & hi-res optical spectroscopy show accretion endures in 1/3 of stars at ~10 Myr in sparse cluster environments. ROSAT discovered the nearest open cluster found in the 20th century: 26 Li-rich, rapidly rotating stars, B9 to M5.5 (+ BDs?). D=97 pc, q=0.5 pc, t=9 Myr. Lawson et al. 2002, Lyo et al. 2003 Lawson et al. 2004 Mamajek et al. 1999 & 2000, Lawson et al. 2001, Lyo et al. 2004

  16. Summary • Flares may have important effects on protoplanetary disks: • ionization & disk dynamics • irradiation & melting of solids (meteoritics) • chemistry & heating • X-rays help determine disk longevities.

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