Disk evolution and Clearing

P. D’Alessio (CRYA)C. Briceno (CIDA)J. Hernandez (CIDA & Michigan)L. Hartmann (Michigan)J. Muzerolle (Steward)A. Sicilia-Aguilar (Heidelberg)Spitzer/IRS disk modeling teamL. Allen (SAO)T. Megeath (SAO)K. Luhman (PenState)

N. Calvet (Michigan)

T. Bergin (Michigan)D. Wilner (SAO)C. Qi (SAO)L. Adame (UNAM)C. Espaillat (Michigan)Z. Zhu (Michigan)R. Franco-Hernandez (SAO/UNAM)

• Disks evolve from optically thick dust+gas configurations to mostly solids debris disks

Disk evolution

HK Tau, Stapelfeldt et al. 1998

•optically thick dust+gas configurations, formed in the collapse of rotating molecular cores•dust/gas ~ 0.01•heated by stellar radiation captured by dust•dust reprocesses heat and emits at IR •collisions transfer heat to gas, determines scale height•accreting mass onto the star

Optically thick disks (T Tauri phase)

Furlan et al 2006Photosphere

Dust

•Spheres of size a with n(a) da = C a-p da, amin, amax

•amin = 0.005m, p=2.5,3.5

•amax=0.1m – 1 cm

•Silicates, organics, amorphous carbon, water ice, troilite

•As amax increases:

1 m

10 mm

10 cm

Less optical-nearIR opacityHigher mm opacity

Dust properties from SED

Median SED of Taurus

amax=0.3m, ISM

amax = 1mm

D’Alessio et al 2001

amax increases, 1 decreases, less heating, less IR emission mm increases, higher fluxes

Disks are accreting

Inner disk is truncated by stellar magnetic field at ~ 3-5 R*. Matter flows onto star following field lines – magnetospheric accretion flow

Hartmann 1998

Evidence for magnetospheric accretion Broad emission linesMuzerolle et al. 1998, 2001

v ~ 0 km/s

v ~ 250 km/s

Excess emission/veiling

velocity

Evidence for magnetospheric accretion Broad emission linesMuzerolle et al. 1998, 2001

Redshifted absorption if right inclination

v ~ 0 km/s

v ~ 250 km/s

Excess emission/veiling Calvet & Gullbring 1998

Measure dM/dt

Optically thin disks (debris disk)

Furlan et al 2006

Chen et al 2006

Optically thin disks (debris disk)

Chen et al 2006

•dust/gas ~ 0.99•small secondary dust, from collisions of large bodies•Large inner holes, tens of AUs•no gas accretion

Questions

•How does gas evolve – dissipate?•How does dust evolve – formation of large bodies?•Characteristic times scales

Compare characteristic properties of populations of different ages

Mass accretion rate decreases with time

Hartmann et al. (1998), Muzerolle et al. (2001), Calvet et al. (2005)

Fraction of accreting objects decreases with time

.50 .23 .12

Viscous evolution - Gas

Accretion at 20 Myr: St34

Binary of two M3 starsAccretingNo Li I absorption => old age

Disk tidally truncated at 0.7AU

Oldest accreting disk so far

White & Hillenbrand 2005

Hartmann et al 2005

Dust emission decreases with age

SEDs of stars in Tr 37 ~ 3 MyrIRAC dataWeaker than median of

Taurus

Taurus median

Phot

Sicilia-Aguilar et al 2005

Fraction of optically thick inner disks decrease with age

•Decrease of fraction of objects with near-IR emission with age•Near-IR from inner, hotter disk

•life-time ~ 5 Myr•large scatter

Hillenbrand, Carpenter, & Meyer 2006

Evolution of grains in disks

•As disk ages, dust growths and settles toward midplane as expected from dust evolution theories

Weidenschilling 1997

Upper layers get depleted

t = 0

Population of big grains at midplane

Dust evolution effects on SED

Decrease of dust/gas in upper layers

Weidenschilling 1997

Lower opacity, less heating, less emission

D’Alessio et al. 2006

Increasing depletion of upper layers

Settling of dust toward midplane

Furlan et al. 2005

Depletion of upper layers: upp/st

Settling of dust toward midplane

Depletion of upper layers: upp/st

Median of Taurus from IRAC fluxes for 60 stars (Hartmann et al 2005) and IRS spectra of ~75 objects (Furlan et al 2005)

~ 0.1 – 0.01Olivines

Furlan et al 2006

Settling of dust toward midplane: smallgrains in upper layers

Sargent et al 2006

•Silicate emission feature formed in hot upper disk layers•Small grains in upper layers•Crystalline components

Crystallinity increases with degree of settling

Sargent et al 2006Watson et al 2006

SED evolution

Taurus 1-2 Myr

Tr 37 3 Myr

NGC 7160 10 Myr

Evolution of the median SED from IRAC and MIPS 24 measurements:Gradual decrease of emission, increased settling

Sicilia-Aguilar et al 2005

Not the end of the storyFraction of inner disks decreases with time

Transitional disks

Calvet et al 2002

TW Hya10 Myr old

Taurus median

Inner disk clearing

Uchida et al. 2004

Spectra from IRS on board SPITZER

TW Hya, ~ 4 AU~ 10 Myr

Inner disk

Wall

Optically thin region with lunar mass amount of micron size dust + gas (accreting star)

Optically thick outer disk

Inner disk clearing

Forrest et al. 2004; D’Alessio et al. 2005

CoKu Tau 4, ~ 10 AU~ 2 Myr

No inner disk, silicate from wall atmosphereNon-accreting star

4 AU

T=150-85 K

d

More disks in transition in Taurus

Calvet et al 2005

Rw ~ 24AUouter disk + inner disk with little dust + gap(~ 5-24AU)

Rw ~ 3 AUonly external disk but accreting star

IRS spectra finely maps wall region

Detection of predicted hole on GM Aur with SMA

Wilner et al 2006

Rw ~ 24AU

Transition disks in Chamaeleon

Espaillat et al 2006

Rw ~ 9 AUOnly external disk Accreting starLarge grains

Inner disk clearing

Search of transitional disks in large populations: IRAC-MIPS 24 observations of clusters and associations in a range of ages

Photospheres

Optically thick disks(Allen et al 2004)

Transitionaldisks

Muzerolle et al 2005

Inner disk clearing

Observations of transition disks in populations of ages 1-10 MyrIndicate

<10% t<1 Myr, ~ 10% few Myrtimescale ~ Ntransition/Ntotal x age ~ few 105 yrs Rapid phase

Accretion onto star is turned off quickly during transition phase(most objects not accreting) for ages > 3 MyrBut in Taurus, most transitional disks accreting

Constraints for models

Inner disk clearing: photoevaporation of outer disk?

UV radiation photoevaporates outer diskWhen mass accretion rate (decreasing by viscous evolution) ~ mass loss rate, no massreaches inner diskRg ~ G M* / cs

2(10000K) ~ 10 AU (M*/Msol)

Evolution with photoevaporation

Evolution without photoevaporation

Rg

Clarke et al 2001

Inner disk clearing:photoevaporation of outer disk?

Prediction: low mass accretion rate and mm flux in transitional disks

But average mass accretion rates and high mm fluxes in GM Aur and DM Tau

Clarke et al 2001

Transitional Disk in a Brown Dwarf

Muzerolle et al 2005 Model: Lucia AdameNo significant UV

Rw = 1AU

Inner disk clearing: planet(s)?

Wall of optically thick disk = outer edge of gap at a few AU

Bryden et al 1999

Giant planet forms in disk opening a gap

Inner gas disk with minute amount of small dust – silicate feature but little near IR excess, bigger bodies may be present

Inner disk clearing: planets?

D’Alessio et al. 2005

CoKu Tau 4, wall at ~ 10 AUNo inner disk

Planet-disk system withplanet mass of 0.1 Mjup

for CoKu Tau 4Quillen et al. 2004

Summary

•Great progress in understanding disk evolution •Spitzer data crucial•Disks evolve accreting mass onto star and dust growing and settling to midplane; phase can last at least ~ 20 Myr•At some point, disk enters into transitional phase, turning off accretion and clearing up inner disk

•fraction of transitional disks increases with time but stabilizes to ~ 10 % after ~ 4 Myr•low proportion of accreting transitional disks at >4 Myr

•Alternative models for clearing are planet formation and photoevaporation of outer disks. Present evidence may favor planet formation •Need characterization of properties of transitional disks in large samples of different ages plus theoretical efforts

Inner disk clearing: planets?

•Tidal truncation by planet •Hydrodynamical simulations+Montecarlo transfer – SED consistent with hole created and maintained by planet – GM Aur: ~ 2MJ at ~ 2.5 AU – Rice et al. 2003

SED depends on mass of planet (and Reynolds number)

0.085 MJ

1.7 MJ

21 MJ

43 MJ

Giant planet formation theories

•Phase 1: Runaway accretion of solids (crossing of planetesimal orbits)•stops when feeding zone depleted•Phase 2:Accretion of gas•Phase 3: Runaway accretion of gas•Several timescales

•Phase 2 shorter if migration included – feeding zone not depleted (Alibert et al 2004)•Many parameters involved – general idea of physical processes

Pollack et al. 1996

12

3

solids

gas

total

Settling: bimodal grain size distribution

Weidenschilling 1997

Wilner et al. 2005

Small + 5-7mm

~ 1/R

Settling of solids: TW Hya

3.5 cm flux ~ constant =>Dust emission

Wilner et al. 2005Jet/wind?Northermal emission?

Dust emission decreases with age

Calvet et al. 2005

Taurus, 1-2 Myr

Ori OB1b, 3-5 Myr

Settling of solids towards the midplane: effects on SED

Furlan et al 2005

Depletion of upper layers: upp/st

= 0.001

=1

Model slopes for a range of and inclinations compared to measured slopes in IRS spectra of Taurus stars

Consistent with 1-0.1% depletion