Transcript Slide 1
X-rays and planet formation Eric Feigelson (Penn State) 1. X-rays from young stars Magnetic reconnection flaring Some results from COUP & XEST 2. Do X-ray flares influence planet formation? Evidence for X-ray irradiation of disks Implications of flare irradiation From Stars to Planets Apr 2007 X-rays and star/planet formation Orion Nebula cluster & proplyd Star formation occurs in molecular cloud cores at T~10-100 K. Planet formation occurs in disks at T ~100-1000 K. This is neutral material (meV). But high energy radiation is present in planet formation environments: keV photons & MeV particles are produced in violent magnetic reconnection flares. Does this influence disk processes? (heating, ionization, chemistry, turbulence, viscosity, shocks, melting & spallation of solids) Theory looks good Is there evidence for X-ray/flare effects in disks, extrasolar planets & meteorites? Fe 6.4 keV & NeII 12.81mm, meteorites Some useful references • X-rays from young stars & stellar clusters Protostars & Planets V review article 2007 Feigelson, Townsley, Guedel & Stassun • ~20 papers from COUP ApJ Suppl Special Issue October 2005 + others 2006-07 • ~15 papers from XEST Special Issue As&Ap 2007 • ~5 papers/month on X-rays SFRs & disks The Chandra Orion Ultradeep Project 13-day observation of the Orion Nebula 1616 COUP sources: 849 low-NH ONC stars 559 high-NH stars, incl. 75 new members 16 foreground stars 159 probable AGN 23 uncertain Getman & 22 others 2005 COUP #1 & #2 COUP: The Movie Extraordinary flares in Orion pre-main sequence stars 1 2 X-ray cts / ks JW 738 K=10.5 Age ~ 10 Myr Mass ~ 1 Mo log Lp = 32.6 erg/s Time (13.2 days) Wolk et al. 2005 COUP #5 X-ray luminosity fn spans 28 < logLx < 32 erg/s Correlation with stellar mass plus scatter There is no X-ray quiet population for M<3 Mo Guedel et al. XEST #1 All X-ray sources are dominated by flares Characteristics of PMS flaring • Orion flares are typically 102 stronger than >X9 solar flares releasing 1035-1036 ergs (0.5-8 keV). Many smaller flares (powerlaw distribution like Sun/stars). • Flares occur every few days and last ~2-20 hrs • Flares unrelated to accretion variations and are independent of presence of disks • Flare lightcurve & spectral evolution are usually similar to solar/stellar flares • X-ray energies often extend to >10 keV Pre-main sequence X-rays are generally not produced by the accretion process ~15-day light curve X-ray flares Optical accretion event No relation seen between X-ray flares and accretion variations in ~800 Orion stars. Stassun et al. 2006/7 COUP #15/16 No difference in X-ray flaring of ~100 Class II vs. Class III Taurus stars. Stelzer et al. XEST #11 Solar/stellar X-rays arise from magnetic reconnection events in the corona X-ray Sun -- Yohkoh Yokohama & Shibata 1998 T Tauri X-rays arise from a complex reconnecting magnetosphere Both smaller (<1 R*) and giant (~10 R*) loops are inferred from COUP Flaccomio et al. 2005 Open accreting field lines Favata et al. 2005 COUP #6 & 7 Closed plasma-filled field lines Resulting X-ray corona (without flares) Jardine et al. 2006 X-ray emission elevated throughout planet formation epoch 1 Mo X-ray levels are roughly constant during Class I-II-III phases 0.5 Mo 0.2 Mo … but drop greatly on the main sequence Preibisch & Feigelson 2005 COUP #4 Three lines of evidence that X-rays irradiate protoplanetary disks 1. Some systems show evidence of X-ray reflection off of the disk: the fluorescent 6.4 keV iron line Imanishi et al. 2001, Tsujimoto et al. 2005, Favata et al. 2005 2. Some systems show soft X-ray absorption attributable to gas in the disks Kastner et al. 2005 3. Some systems show [NeII] IR line Glassgold et al. 2006, Pascucci et al. 2007 Iron fluorescent line Cold disk reflects flare X-rays COUP spectra YLW 16A: protostar in Oph Imanishi et al. 2001 Tsujimoto & 7 others 2005 COUP #8 X-ray absorption by gas in edge-on Orion proplyds First measurement of gas content of UV-irradiated photoevaporating disks? Kastner & 7 others 2005 COUP #9 X-ray influence on planet formation Mag field lines Cosmic rays Flare X-rays Proto-Jupiter Proto-Earth Flare MeV particles Dead zone Feigelson 2003, 2005 Ionized MHD turbulent zone X-rays & disk ionization YSO X-ray ionization rate dominates CRs in the disk by 108 for 1Mo PMS star at 1 AU: z = 6x10-9 (Lx/2x1030 erg s-1) (r/1 AU)-2 s-1 The ionization fraction is uncertain due to recombination processes. Hard (5-15 keV) X-rays should penetrate 1-100 g/cm2. Igea & Glassgold 1997 & 1999; Fromang et al. 2002; Matsumura & Pudritz 2003 & 2006; Alexander et al. 2004; Salmeron & Wardle 2005; Ilgner & Nelson 2006; Glassgold et al. 2007; Nomura et al. 2007 Reviews: Glassgold et al. 2000 PPIV & 2006; Balbus ARAA 2003; Dutrey et al. PPV 2007; Bergin et al. PPV 2007 Plausible X-ray/flare effects on protoplanetary disks • PMS X-ray ionization will heat gas and change chemistry in disk outer layers. • PMS X-rays may be an important ionization source at the base of bipolar outflows. • X-ray ionization is likely to induce MRI turbulence affecting accretion, planetesimal formation, migration, ... • Flares may help explain enigmas in the meteoritic record: short-lived radionuclides, chondrule flash melting X-ray ionization of the gaseous disk PREDICTION Atomic excitation calculation of J1/2 J3/2 [NeII] 12.81 mm line from ionized outer layer of disks around 5-10AU Glassgold et al. 2006 DETECTION Spitzer FEPS Legacy reports [Ne II] line in 4 older, X-ray bright T Tauri stars Pascucci et al. 2007 Protoplanet migration in a turbulent disk X-rays MRI MHD turbulence inhomogeneities producing gravitational torques which overwhelm the Goldreich-Tremaine torque, so protoplanets undergo random walks rather than secular Type I migration. Gap formation suppressed. Laughlin et al. 2004 and other groups Conclusions • The X-ray studies of young stars show that powerful magnetic flares are ubiquitous throughout the epoch of planet formation. The astrophysics resembles solar flares • X-rays can efficiently irradiate protoplanetary disks Evidence: Possible consequences: Fe fluor lines Absorption Ionization Turbulence Heating Chemistry Chondrule melting Outflows CAI isotopes Therefore ….. Planetary systems form in cool dark disks …. which are irradiated by 10 8 violent magnetic reconnection flares