X-ray effects on protoplanetary disks

Eric Feigelson (Penn State University)

1. Review of X-ray flaring from YSOs

2. Evidence for X-ray irradiation of disks

3. Consequences of X-ray irradiation

Theme

We see how stellar magnetic fields

can influence disk magnetic fields

through the high-energy radiation

of violent reconnection events

Chandra Orion Ultradeep Project13 days nearly-continuous observation in 200322 papers, 2005-08 (Getman et al. 2005)

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Solar/stellar X-rays arise from magnetic reconnection events of fields erupted

from the stellar interiors

X-ray Sun -- Yohkoh

Yokohama & Shibata 1998

Theoretical calculations of pre-main sequence magnetospheres

Donati et al. 2007, Jardine et al. 2006

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Magnetically funneled accretion on open field lines Magnetic reconnection flares from closed field lines

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Long et al. 2007, Romanova et al. 2008

X-ray flares are strong and ubiquitous in

pre-main sequence stars throughout the planet formation era

• Elevated X-ray flaring seen in thousands of PMS stars in dozens of star forming regions. 28 < log Lx < 32 erg/s.

• For 1 MO stars, flares are ~102 more luminous and ~102 morefrequent than in contemporary Sun.

• X-ray flare levels strongly correlated with stellar mass, Lx~M1.8

Not correlated with rotation (Fossil field? Magnetosphere truncation? Convective dynamo saturation?)

• X-ray flare levels rise slightly from Class I-II-III phases,(t~105-107 yrs), and decay during main sequence(t~108-1010 yrs). Not convincingly seen in Class 0, butlikely present.

Feigelson et al. (2007) PPV review. Studies include:Wolk et al. (2005), Preibisch et al. (2005), Preibisch & Feigelson (2005), Telleschi et al. (2007), Stelzer et al. (2007), Giardino et al. (2007), Carramazza et al. (2007), Prisinzano et al. (2008)

X-ray spectrum of a high-Lx Orion star

Note that pre-2000 studies showed only <2 keVdue to poor telescopes. Chandra/XMM see <8 keV

and models sometimes infer X-rays out to 15-20 keV.

1 keV5 keV10 keV

Maggio et al. 2007

Some T Tauri flares are extraordinarily hotand arise in extraordinarily large loops

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Solar flares

Older active stars

Orion bright flares

Superhot flares

Getman et al. 2008a

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Evidence formagnetosphereconfinement bydisk

Getman et al. 2008b

Loop

siz

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radi

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H-K excess

Rarely mentioned ….

Flare X-rays must irradiate disks

The mid-IR spectral energy distribution of YSO disksrequires they be illuminated by photospheric light giving a `flared’ structure. Chiang & Goldreich 1997; PPV review by Dullemond et al. 2007

As the X-rays are formed above the stellar surface,geometrically they also should illuminate the disk.

Dead zone Ionized MHDturbulent zone

Cosmic rays

Flare X-rays

Flare MeV particles

Mag field lines

Proto-Jupiter

Proto-Earth

Feigelson 2003, 2005, 2010

X-ray influence on protoplanetary disks

Typical model of a disk with X-ray irradiationIlgner & Nelson 2006abc

Density

Ionization: X-rays penetrate tomidplane outside ~1-5 AU

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Evidence that stellar X-rays irradiate protoplanetary disks

1. Some systems show soft X-ray absorption attributable to gas in the disks

2. Some systems show evidence of reflection of X-rays off of the disk: the fluorescent 6.4 keV iron line

3. Some disks show [NeII] 12.8m line from X-ray ionization

4. Many disks show a non-equilibrium hot molecular layer, excited H2, H2O and CO from X-ray or UV irradiation

X-ray absorption by gas in edge-on Orion proplyds

Kastner et al. 2005

Iron fluorescent lineCold disk reflects flare X-rays

Tsujimoto et al. 2005, Favata et al. 2005, Giardino et al. 2007, Skinner et al. 2007, Czesla & Schmitt 2007 Review by Gudel & Naze 2009

YLW 16A: protostar in Oph Imanishi et al. 2001

Best ca

se!

Stellar X-rays ionize and heat outer disk atmospheres

[Ne II] 12.81 m line predicted

Glassgold et al. 2006; Meijerink et al. 2008; Ercolano et al. 2008/9/10; Alexander 2008; Gorti & Hollenbach 2008; Glassgold et al. 2009;Schisano et al. 2010; Shang et al. 2010;Owen et al. 2010

[Ne II] line detected with Spitzer and 8m telescopesPascucci et al. 2007; also Lahuis et al. 2007; Herczeg et al. 2007; Najita et al. 2009/10;;Flaccomio et al. 2009; Pascucci & Sterzik 2009

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Hot CO and H2O seen in some PPDs

Carr et al. 2004

H2O

CO

X-rays are the principal source of disk ionization

YSO X-ray ionization rate dominates CRs in the

disk by 108 for 1Mo PMS star at 1 AU:

= 6x10-9 (Lx/2x1030 erg s-1) (r/1 AU)-2 s-1

The ionization fraction is uncertain due to recombination processes. Hard (5-20 keV) X-rays should penetrate 1-100 g/cm2. Igea & Glassgold 1997 & 1999; Fromang, Terquem & Balbus 2002;Matsumura & Pudritz 2003/6/8/9; Alexander, Clarke & Pringle 2004; Salmeron & Wardle 2005; Ilgner & Nelson 2006abc; Turner et al. 2009/10;Ercolano et al 2009/10; Reviews: Glassgold et al. 2000 & 2006; Balbus 2003

Theorists modeling ionized disksare strongly encouraged to use …

realistic broad-band X-ray spectra,realistic range of X-ray luminosities,

and (when relevant) realistic X-ray variability

also please mention role of X-rays as likely principal source of disk ionization

with reference to the data

Plausible X-ray/flare effects on protoplanetary disks

• PMS X-ray ionization will heat gas and change chemistry in disk outer layers

Aikawa & Herbst 1999 and dozens of studies

• PMS X-rays may be an important ionization source at the base of bipolar outflows

Shang et al. 2002 and a few studies

• X-ray ionization is likely to induce MRI turbulence affecting accretion, dust coagulation, protoplanet migration, gaps

Glassgold et al 1997 and dozens of studies

• Flare energetic particles and shocks may explain meteoritic mysteries (chondrule melting, short-lived radionuclides)Shu et al. 1997 and a few studies

Conclusions

• The X-ray studies of young stars show that powerful magnetic flares are ubiquitous throughout the epoch of planet formation, 103 above solar levels. The astrophysics resembles gigantic solar flares.

• X-rays can efficiently irradiate protoplanetary disks.X-ray evidence: Fe fluor lines AbsorptionIR evidence: [NeII] line Mol. excitation

Possible consequences MRI, turbulence, viscosity, etcon planet formation Gas heating & ion-molecular chemistry processes: Ionization of outflows

Spallation of isotopes, chondrule melting