barbara ercolanobarbara ercolano university of exeter tuesday, 27 july 2010 tuesday, 27 july 2010...

Thanks to:James Owen, C. Clarke (IoA); A. Glassgold (Berkeley);

S. Mohanty (Imperial); N. Turner (JPL); J. Drake, J. Raymond (CfA)

X-ray irradiated protoplanetary discs

Barbara Ercolano University of Exeter

Tuesday, 27 July 2010

X-ray Feedback on Low Mass Star & Planet Formation

Taurus – Spitzer Space Telescope




Gued

el e

t al.,

200

7


What drives the dispersal of disks? On what timescales?

What environments are favourable to the formation of terrestrial and giant planets?

What is the effect of irradiation on planetary atmospheres?




Credit: NASA/LMSAL


X-Rays


X-RaysMRI


X-Rays

Dead Zone

Proto-Earth

MRI


X-Rays

Dead Zone

Proto-Earth

Proto-Jupiter

Photoevaporation

migration

MRI


•‘Hard’ X-rays: MRI and Dead Zones

•‘Soft’ X-rays: Disc photoevaporation

Overview




Overview

‘Hard’ : E > 1 keV

‘Soft’ : 0.1 < E < 1 keV


•MRI and Dead Zones

•Igea & Glassgold 1999

•X-rays from YSO dominate the disc ionisation structure

•Discs around solar-type stars mostly MRI active

•Dead-zone should extend to aprrox 5 AU


•Igea & Glassgold 1999


•Turner & Sano 2008•Turner & Drake 2009

•Dead or Undead?

•Use IG99 ionisation rates for stellar X-ray & consider other ionisation processes in the MMSN

•Dead zones basically always present

•Undead zones important?

•MRI active

•dead•undead


•Mohanty, Ercolano & Turner 2010 in prep

•MRI & (Un)Dead Zones in YSO Discs

•New ionsation rates calcs with MOCASSIN

•Chemical network to account for recombinations on grains

•Parameter space investigation


•Mohanty, Ercolano & Turner 2010 in prep

•MRI & (Un)Dead Zones in YSO Discs

•New ionsation rates calcs with MOCASSIN

•Chemical network to account for recombinations on grains

•Parameter space investigation

•DZ present in all discs with Md > 1% M*

•MRI is reduced for discs with small grains or low densities

•Grains play a major role in determining accretion in discs




Overview

‘Hard’ : E > 1 keV

‘Soft’ : 0.1 < E < 1 keV


high mass

Viscous evolution predicts….

high accretion rate

time

low mass

low accretion rate


high mass


Observations instead show….

t~106yrs t~107yrs

high accretion rate

time

low mass

low accretion rate


high mass


Observations instead show….

t~106yrs t~107yrsRare transition disk

high accretion rate

time

low mass

low accretion rate


Alexander, based on a description of viscous evolution

Viscous evolution

Ac

cr

etio

n r

ate

The Classical EUV switch modelClarke et al. (2001); Matsuyama et al. (2003);

Ruden (2004)

Time



Viscous evolution

Wind rate

Ac

cr

etio

n r

ate


Ruden (2004)

Time



Viscous evolution

Wind rate

Viscous +windAc

cr

etio

n r

ate


Ruden (2004)

Time


Modelling photoevaporating disks: HOW?

Ercolano+ 2008, 2009, Owen+ 2010, Ercolano & Clarke 2010, Ercolano & Owen 2010, Owen, Ercolano & Clarke 2010


Modelling photoevaporating disks: HOW?

1) Radiative Transfer (MOCASSIN) a) 2D (at least) b) gas (photoionisation) + dust 2) Hydrodynamics (ZEUS)

3) Viscous Evolution

Ercolano+ 2008, 2009, Owen+ 2010, Ercolano & Clarke 2010, Ercolano & Owen 2010, Owen, Ercolano & Clarke 2010


Owen, Ercolano, Clarke & Alexander, 2010


Owen, Ercolano, Clarke & Alexander, 2010

Total photoevaporation rate of ~1.4e-8 Msun/yr

(for Lx = 2e30erg/sec)

Comparable to accretion rates of CTTs


Owen, Ercolano, Clarke & Alexander, 2010Tuesday, 27 July 2010

Ow

en, E

rcol

ano

& C

lark

e 20

10, i

n pr

ep

0

2

4

log(Surface Density) [g cm 3]

log(

Surfa

ce D

ensi

ty) [

g cm

3 ]

0.1 1 10 10010 11

10 10

10 9

10 8

Radius [AU]

Accr

etio

n R

ate

[M

yr1 ]

!

No photoevaporation

Photoevaporation


Ow

en, E

rcol

ano

& C

lark

e 20

10, i

n pr

ep

0

2

4

log(Surface Density) [g cm 3]

log(

Surfa

ce D

ensi

ty) [

g cm

3 ]

0.1 1 10 10010 11

10 10

10 9

10 8

Radius [AU]

Accr

etio

n R

ate

[M

yr1 ]

!

No photoevaporation

Photoevaporation

Photoevaporation-starved accretion?


Why do non-accreting YSOs (WTTs) have higher LX than accreting YSOs (CTTs) ??


Accretion ‘disturbs’ X-ray emission

(e.g. Flaccomio et al 2003, Stassun et al 2004, Preibisch et al 2005, Jardine et al 2006, Guedel et sl 2007, Gregory et al 2007)



Accretion ‘disturbs’ X-ray emission

(e.g. Flaccomio et al 2003, Stassun et al 2004, Preibisch et al 2005, Jardine et al 2006, Guedel et sl 2007, Gregory et al 2007)


X-rays modulate accretion?X-ray photoevaporation-starved accretion

(Drake et al 2009)


Drake et al 2009


Ow

en, E

rcol

ano

& C

lark

e 20

10, i

n pr

ep

0 2 4 6 8 10 121028

1029

1030

1031

Time [Myr]

Xra

y Lu

min

osity

[erg

s1 ]

WTTs (discless)

CTTs (discbearing)

Data points from Taurus (Guedel et al 2007)


Ow

en, E

rcol

ano

& C

lark

e 20

10, i

n pr

ep

10.5 10 9.5 9 8.5 8 7.5 7

log(Accretion Rate) [M yr 1]

29

29.5

30

30.5

31

11 10.5 10 9.5 9 8.5 8 7.528.5

29

29.5

30

30.5

log(

Xra

y Lu

min

osity

) [er

g s

1 ]

!Log(Accretion Rate) [Msun/yr]

Log(

X-r

ay L

umin

osity

) [e

rg/s

ec]

0.5-3.5 Myr 1.5-4.5 Myr

4-8 Myr integrated lifetime


Conclusions

X-rays control the evolution & dispersal of protoplanetary discs

& affect planet formation through:


•Ionising the discs thus allowing MRI to work•(‘hard’ x-ray)

•Driving a photoevaporative wind that erodes the disc from the inside-out•(‘soft’ X-ray)

•(Possibly) modulating accretion through photoevaporation-starved accretion•(‘soft’ X-ray)

Conclusions

X-rays control the evolution & dispersal of protoplanetary discs

& affect planet formation through:


Thank You!


barbara ercolanobarbara ercolano university of exeter tuesday, 27 july 2010 tuesday, 27 july 2010...

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