Outflows from protoplanetary disks
and star-disk interaction
原始惑星系円盤からのアウトフローと円盤と中心星の相互作用

Shinsuke Takasao (Nagoya Univ.)
collaborators:

T.K. Suzuki (Univ. Tokyo),
K. Tomida (Osaka Univ.),
and K. Shibata (Kyoto Univ.)

Structure of outflows from CTTSs
fast/warm

slow/coole.g. Bacciotti+2000
Takami+2002
Schneider+2013

observed in a wide range of wavelength :radio - IR - optical - UV
T  105 K

Discovery of X-ray outflows
Outflows~700 AU

Chandra discovered X-ray outflows
from CTTS DG Tau (Gudel+2008)
Along the optical jets
Length : ~several 100 auTemperature: 3.4 MK (!!)
111
Mass loss rate: 1.3 ⇥ 10 M yr(Schneider & Schmitt 2008)

Strong soft X-ray emission at the base of the outflows
291L⇡
10ergs(within a few 10 au from the star): X(~10 % of the stellar hard X-ray component, Gudel+2011)

Other CTTS examples (T ~ a few - several MK):
Z CMa (Stelzer + 2009), L1551 IRS 5 (Schneider + 2013)
RW Aur (Skinner & Gudel 2014), RY Tau (Skinner + 2016)

Impact of outflow X-rayson the disk ionization degree
Most of the outflow X-rays (10^29 erg/s)
are coming near the base (<20-30 au, Gudel+2011)
Ionization degree
Ratio of(radio active nuclei, cosmic rays,the ion. deg. with the outflow XRs @ 10auand stellar X-rays)
to the ion. deg. without the outflow XRs⇥10 13Enhancement
MRI active

Shrinkage ofdead zone

dead zone(Essentially the same as Sano+2000 model but stellar X-rays included)

Questions
What is the heating/driving mechanisms ?
Where is the most X-ray luminous region in the outflow?
(not resolved. should be within ~30 au from the star)Important if it is moderately close to the disk(<~10 au)depends on the heating mechanisms.
Are X-ray outflows persistent or transient ?
Are X-ray outflows a common feature for YSOs ?

Puzzles about heating mechanisms
X-ray count rate

~6yr obs of DG Tau
X-ray from the star:
highly time-variable

time

X-ray from the outflow
base : quasi-steadyover ~6yrs (Gudel+2011)

Stellar corona/wind ? Probably No.
Accretion shock ? Ambiguous, but maybe not for DG Tau.

(Gudel + 2011)⇣ v⌘2jumpShock heating ? Very difficult. T ⇡ 3.8 MK
500 km s 1

Need very large v and shock at the base (not observed)(Raga + 2002)

Our approach :Magnetic heating in the disk atmosphere
B field amplified by MRIGood example of the magneticallyheated atmosphere:
Solar corona (~1MK)
Suzuki & Inutsuka 2014
low plasma beta in the upper disk

Flock+2011

credit: TRACE/NASAOur approach :Magnetic heating in the disk atmosphere
B field amplified by MRI

X-ray outflow

Suzuki & Inutsuka 2014

hot disk corona

low plasma beta in the upper disk

Magnetic heating may account forthe quasi-steady heating at the base

We developed a theoretical model ofFlock+2011 X-ray outflows from a hot disk corona
ST, Suzuki, and Shibata, submitted to ApJOur approach :Magnetic heating in the disk atmosphere
Shock

X-ray outflow

hot disk corona

Shock heating picture

Magnetic heating may account for
the quasi-steady heating at the base

We developed a theoretical model of
X-ray outflows from a hot disk corona
ST, Suzuki, and Shibata, submitted to ApJOur approach :Magnetic heating in the disk atmosphere
3. Outflow property(T, mass loss rate, velocity)
2. Driving mechanism

X-ray outflow

hot disk corona

1. Thermal property at the base(T, density, …)
Magnetic heating may account for
the quasi-steady heating at the base

We developed a theoretical model of
X-ray outflows from a hot disk corona
ST, Suzuki, and Shibata, submitted to ApJSupply and dissipation of magnetic energy
Rise of a magnetic loop

(e.g. Hirose & Turner 2011, Io & Suzuki 2014)

field lines

image ofsolar corona

Resol. ~100km
Cirtain + 2013

magnetic reconnection heating

Example of heating by 3D reconnectionSupply and dissipation of magnetic energy
Rise of a magnetic loop

(e.g. Hirose & Turner 2011, Io & Suzuki 2014)

field lines

magnetic reconnection heating

B2
Energy released by reconnection : emag = f8⇡

Energy injection timescale : ~ growth timescale of Parker instability

emag
Heating rate [erg/s/cm^3]: EH =⌧P⌧PDisk coronal temperature & density:
energy balance between the heating and cooling
In a quasi-steady state,heating ~ conduction cooling ~ radiative cooling(1)(2)
HeatingConduction
Radiation

credit: TRACE/NASA(1) determines the temperature(2) determines the density(called RTV scaling law)
The thermal property at the basecan be determined.

Scaling relations : coronal temperature
Disk model (Kusaka + 1970)
⇣

⌘ 3/4
r
Tdisk = 103
K
0.1 au⇣ r ⌘ 15/8
⇢disk = 10 8
g cm 30.1 au6Tc ⇡ 3.4 ⇥ 10 K

✓

M⇤
M

◆ 1/7 ✓

Disk plasma beta

disk100◆ 3/7 ⇣r ⌘ 15/28
0.1 auWe confirm that the outflow temperature should be similar to the coronaltemperature Tc, because we can neglect cooling effects during its propagation.

Consistent !

Temperature: 3.4 MK (Gudel+2008)
Mass loss rate: 1.3 ⇥ 10 11 M yr 1

(Schneider & Schmitt 2008)

Scaling relations : Mass loss rate
Mass loss rate:Ṁ = (⇢Av)base

Coronal density

✓M⇤
Myr✓

⇢c ⇡ 3.1 ⇥ 10

17g cm3◆3/14 ✓

disk100◆ 6/7 ⇣r ⌘ 123/56
0.1 auThe velocity depends on the driving mechanism (magnetic pressure,magnetocentrifugal, etc. Kudoh & Shibata 1997) : MagnetocentrifugalṀ ⇡ 2.5 ⇥ 1011M

1M⇤M◆1/14 ✓

disk100◆ 9/7 ⇣r ⌘43/28
0.1 auConsistent !

Temperature: 3.4 MK (Gudel+2008)
Mass loss rate: 1.3 ⇥ 10 11 M yr 1(Schneider & Schmitt 2008)

What can we learn?
The X-ray luminous region will be near the disk=> Possible significant impact on the disk
(dead-zone size, non-ideal MHD effects)

The disk B can be inferred from the outflow temperature T:

B ,disk ⇡ 20 G✓

Tc
4.0 ⇥ 106 K◆7/6 ⇣

r0.1 au⌘ 11/16

3D MHD modeling
Inner disk structure: star-disk interaction important
We started 3D MHD modeling using the Athena ++ codedeveloped by the Princeton team and K. Tomida.

Summary
We developed a theoretical model of X-ray outflows
from young stellar objects. In this model magnetic
reconnection in the disk atmosphere plays an importantrole in heating the outflows.
The estimated temperature and mass loss rate areconsistent with observations in the case of the fieldstrength of ~20 G and the heating region is < 0.1 au.
Our scaling relation for the temperature will be usefulfor estimating the field strength.
We started MHD simulations of the star-disk interaction.