Download Feigelson, E. (PSU)

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