High Energy Processesin Young Stellar Objects

Ji Wang

Department of Astronomy

University of Florida

Young Stellar Objects

• History– Collapsing rotating cloud

• Laplace 1796

– T Tauri Star• Alfred Joy 1945• Features (interior, surface, • luminosity)

White & Hillenbrand 2004

Observation

• Outflows– P cygni line profile

• Disk– By millimeter interferometer and HST

• Accretion– Evelope-disk-star

• Magnetic activity– Flare

Stages of YSOs

• Class 0 (10^4 yrs)– Massive cold evelope – Disk, outflow formed

• Class I (10^5 yrs)– Disk appears– Larger outflowing angle – Lower mass loss rate

• Class II, CTT (10^6 yrs)– Outflow exists in young stage– Strong wind

• Class III, WTT (10^6 yrs)– Simple Blackbody SED

• Post T Tauri– Long missing from YSO sample– Emerging from X-ray surveys– Distinguished by lithium abundance

van Dishoeck and Blake 1998, ARAA 36, 317

Stages of YSOs

Feigelson 1999

Origins of X-ray

• Magnetic field rooted at star surface are resposible for flaring– Enhanced solar-type magnetic-activity– a-w dynamo

• Successfully explains butterfly diagram• But fails when comes to fully convective situation

– Alternatives• Release of gravitational energy (Lamzin 1996)• Colliding CTT star winds (Zhekov 1994)

• Star-disk interaction– Successfully explains generation of wind and collimated outflows– Challenged by by growing argument over field structure far

larger than those seen on the Sun– Dipole magnetic geometry and steady-state assumption are too

simple to be ture

Possible magnetic geometries in YSOs

Feigelson 1999

Five possibilities• Solar type multipolar fields with both footprints rooted in stellar

photosphere– a-w type dynamo applicable– Fossil fields inherited from parent molecular cloud

• Field line connecting the star to circumstellar disk at corotation radius– Supported by rotation spin down– Magnetically funneled accretion– Collimated outflows in CTT stars

• Field lines above corotation radius• Magnetic loop with both feet in the disk• Binary YSOs but less important• Reconnection and displacement of footprint are more likely to occur

in YSOs due to more possible magnetic configuration offered by star-star, star-disk, disk-disk interaction

Tracer of magnetic activity

• X-ray emission– Continuous emission, optically thin thermal bresmsstrahlung with

associated ionized metal emisson lines from multitemperature plasmas with 1<Tx<100MK (Montmerle 1991)

– Powerful flares (T~10^6-10^8 K)– Plasma density and magnetic strength can be inferred

• Optical studies– Zeeman effect– Star spot– Chromosphere

• Gyrosymchrotron radio-continuum– Highly variable– Produced by mildly relativistic electrons with energy around 1

MeV spiraling in ~1 G fields (Dulk 1985)

X-ray properties of T Tauri stars• CTT stars and WTT stars are similar in the context of X-

ray properties because it demostrate little or no dependence on disk interaction

• X-ray T Tauri Stars are variable (days), sometimes show high amplitude flare with time scale of hours

• Spectra can be modeled as soft component (Tx~2-5 MK) and hard component (Tx~15-30 MK) or higher temperature component

• Relations between X-ray luminosity and stellar properties– Lx/Lbol~10^-3– Lx~rotation indicator– Fx~Stellar surface temperature– X-ray luminosity mass correlation

Effects on circumstellar environment

• Ionization

• Heating

• Modification of gas chemistry

• Changing grain composition

Ionization and heating• Ionization-coupling gas and magnetic field

– Low ionization– Regulating accretion and wind– Coupling disk and outflow– Affecting planetary formation

• Compared with UV photons– Extended region of low ionization zone– Have potential effect even in deeply embedded environment– Dominating cosmic ray ionization ~4000AU (Krolic & Kallman 1983)

• Ionization mechanism– Photoionization~1 KeV– Compton ionization~20 KeV– Cross section~E^-2.5 and Z^3

• Continuous heating source in Molecular Cloud– Recombination time 10 yrs– Flare recurrence time considerably less than 10 yrs– Dominant source within 0.1 Pc in MC

Conclusion

• High energy processes are prevalent in low mass YSOs

• If X-ray emission begins in the earliest Class 0 phase, then YSO ionization may crucially affect the gravatational collapse of star formation

• X-ray emission is prevalent in the Class I-II phases, X-ray ionization is quite likely to play a central role in the astrophysics and evolution of the circumstellar disk

– Introduction of MHD turbulence and viscosity, thereby regulating accretion onto the star

– Magnetically coupling star to disk, and disk to outflow

Referrences• Feigelson, E. D., & Montmerle, T. 1999, ARA&A, 37, 363

• Lamzin SA, Bisnovatyi-Kogan GS, Errica L,Giovannelli F, Katysheva NA, Rossi C, Vittone AA. 1996. Astro. Astrophys. 306:877-91

• Zhekov AS, Palla F, Myasnikov AV. 1994. MNRAS 271:667-75

• Monterle T, Feigelson ED, Bouvier J, Andre P. 1993. In Levy & Lunine 1993, 689-717

• Dulk GA. 1985. Annu. Rev. Astron. Astrophys. 23:169-224

• Krolik JH, Kallman TR. 1983. Astrophys. J. 267:610-24

• Chandra Orion Ultradeep Project census of X-ray stars in the BN-KL and OMC-1S regionsN. Grosso, E. D. Feigelson, K. V. Getman, L. Townsley, P. Broos, E. Flaccomio, M. J. McCaughrean, G. Micela, S. Sciortino, J. Bally, N. Smith, A. A. Muench, G. Garmire, F. Palla

• X-ray Emission from Orion Nebula Cluster Stars with Circumstellar Disks and JetsJoel H. Kastner, Geoffrey Franz, Nicolas Grosso, John Bally, Mark J. McCaughrean, Konstantin Getman, Eric D. Feigelson, Norbert S. Schulz

• Bright X-ray flares in Orion young stars from COUP: evidence for star-disk magnetic elds?F. Favata, E. Flaccomio, F. Reale, G. Micela, S. Sciortino, H. Shang, K. G. Stassun, E. D. Feigelson

• The Origin of T Tauri X-ray Emission: New Insights from the Chandra Orion Ultradeep ProjectThomas Preibisch, Yong -Cheol Kim, Fabio Favata, Eric D. Feigelson, Ettore Flaccomio, Konstantin Getman, Giusi Micela, Salvatore Sciortino, Keivan Stassun, Beate Stelzer, Hans Zinnecker

OMC 1-South cloud core http://www.astro.psu.edu/coup/Protostars.html

McCaughrean 2005

Grosso et al 2005

Kastner et al 2005

Favata et al 2005

Preibisch et al 2005

Hartmann 1997

Thank you