disk evolution and clearing p. d’alessio (crya) c. briceno (cida) j. hernandez (cida &...
Post on 21-Dec-2015
216 views
TRANSCRIPT
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