Transcript INSTITUTO DE ASTRONOMIA UNAM CAMPUS MORELIA

Disk evolution and Clearing
N. Calvet (Michigan)
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 team
L. Allen (SAO)
T. Megeath (SAO)
K. Luhman (PenState)
T. Bergin (Michigan)
D. Wilner (SAO)
C. Qi (SAO)
L. Adame (UNAM)
C. Espaillat (Michigan)
Z. Zhu (Michigan)
R. Franco-Hernandez (SAO/UNAM)
Disk evolution
• Disks evolve from optically thick dust+gas
configurations to mostly solids debris disks
HK Tau, Stapelfeldt et al. 1998
Optically thick disks (T Tauri phase)
Photosphere
Furlan et al 2006
•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
Dust
•Spheres of size a with
n(a) da = C a-p da, amin, amax
•amin = 0.005mm, p=2.5,3.5
•amax=0.1mm – 1 cm
•Silicates, organics,
amorphous carbon, water ice,
troilite
•As amax increases:
Less optical-nearIR opacity
Higher mm opacity
1 mm
10 mm
10 cm
Dust properties from SED
Median SED of Taurus
amax = 1mm
amax=0.3mm, ISM
D’Alessio et al 2001
amax increases, k1m decreases, less heating, less IR emission
kmm 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
Excess emission/veiling
Broad emission lines
Muzerolle et al. 1998, 2001
v ~ 250 km/s
v ~ 0 km/s
velocity
Evidence for magnetospheric accretion
Excess emission/veiling
Calvet & Gullbring 1998
Broad emission lines
Muzerolle et al. 1998, 2001
v ~ 250 km/s
Measure dM/dt
v ~ 0 km/s
Redshifted
absorption if right
inclination
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
Viscous evolution - Gas
.50 .23 .12
Hartmann et al. (1998),
Muzerolle et al. (2001),
Calvet et al. (2005)
Fraction of accreting objects decreases with time
Accretion at 20 Myr: St34
White & Hillenbrand 2005
Hartmann et al 2005
Binary of two M3 stars
Accreting
No Li I absorption => old age
Disk tidally truncated at 0.7AU
Oldest accreting disk so far
Dust emission decreases with age
SEDs of stars in Tr 37
~ 3 Myr
IRAC data
Weaker than median of
Taurus
Sicilia-Aguilar et al 2005
Taurus
median
Phot
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
t=0
Upper
layers get
depleted
Population
of big
grains at
midplane
Weidenschilling 1997
Dust evolution effects on SED
Decrease of dust/gas in
upper layers
Lower opacity, less heating, less
emission
Increasing
depletion of
upper layers
z
Weidenschilling 1997
D’Alessio et al. 2006
Settling of dust toward midplane
Depletion of upper layers: zupp/zst
Furlan et al. 2005
Settling of dust toward midplane
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 – 0.01
Olivines
Depletion of upper layers: zupp/zst
Furlan et al 2006
Settling of dust toward midplane: small
grains in upper layers
•Silicate emission feature formed in hot upper disk layers
•Small grains in upper layers
•Crystalline components
Sargent et al 2006
Crystallinity increases with degree of
settling
Watson et al 2006
Sargent et al 2006
SED evolution
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 story
Fraction of inner disks decreases with time
Taurus 1-2 Myr
Tr 37 3 Myr
NGC 7160 10
Myr
Transitional disks
TW Hya
10 Myr old
Taurus median
Calvet et al 2002
Inner disk clearing
Spectra from IRS on board SPITZER
TW Hya, ~ 4 AU
~ 10 Myr
Wall
Optically thick
outer disk
Optically thin region with
lunar mass amount of
micron size dust + gas
(accreting star)
Inner
disk
Uchida et al. 2004
Inner disk clearing
CoKu Tau 4, ~ 10 AU
~ 2 Myr
T=15085 K
4
AU
td
No inner disk, silicate from
wall atmosphere
Non-accreting star
Forrest et al. 2004;
D’Alessio et al. 2005
More disks in transition in Taurus
IRS spectra finely maps wall region
Rw ~ 24AU
outer disk +
inner disk with
little dust + gap
(~ 5-24AU)
Rw ~ 3 AU
only external
disk but
accreting star
Calvet et al 2005
Detection of predicted hole on GM Aur with SMA
Rw ~ 24AU
Wilner et al 2006
Transition disks in Chamaeleon
Rw ~ 9 AU
Only external
disk
Accreting star
Large grains
Espaillat et al 2006
Inner disk clearing
Search of transitional disks in large populations: IRAC-MIPS 24
observations of clusters and associations in a range of ages
Optically thick disks
(Allen et al 2004)
Muzerolle et al 2005
Photospheres
Transitional
disks
Inner disk clearing
Observations of transition disks in populations of ages 1-10 Myr
Indicate
<10% t<1 Myr, ~ 10% few Myr
timescale ~ 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 Myr
But in Taurus, most transitional disks accreting
Constraints for models
Inner disk clearing: photoevaporation of outer
disk?
Evolution
with
photoeva
poration
Rg
Evolution
without
photoeva
poration
Clarke et al 2001
UV radiation photoevaporates outer disk
When mass accretion rate (decreasing by
viscous evolution) ~ mass loss rate, no mass
reaches inner disk
Rg ~ G M* / cs2(10000K) ~ 10 AU (M*/Msol)
Inner disk clearing:photoevaporation of outer disk?
Prediction: low mass
accretion rate and mm flux in
transitional disks
Clarke et al 2001
But average mass accretion
rates and high mm fluxes in
GM Aur and DM Tau
Transitional Disk in a Brown Dwarf
Rw = 1AU
No significant UV
Muzerolle et al 2005
Model: Lucia Adame
Inner disk clearing: planet(s)?
Giant planet forms in disk opening a gap
Wall of optically
thick disk = outer
edge of gap at a few
AU
Bryden et al 1999
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?
CoKu Tau 4, wall at ~ 10 AU
No inner disk
D’Alessio et al. 2005
Planet-disk system with
planet mass of 0.1 Mjup
for CoKu Tau 4
Quillen 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)
21 MJ
1.7 MJ
0.085 MJ
43 MJ
Giant planet formation theories
Pollack et al. 1996
•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
3
1
2
total
solids
gas
Wilner et al. 2005
Settling: bimodal grain
size distribution
Small +
5-7mm
Weidenschilling 1997
~ 1/R
Settling of solids: TW Hya
3.5 cm flux ~ constant =>
Dust emission
Jet/wind?
Northermal emission?
Wilner et al. 2005
Dust emission decreases with age
Taurus, 1-2 Myr
Ori OB1b, 3-5 Myr
Calvet et al. 2005
Settling of solids towards the midplane:
effects on SED
Model slopes for a range of 
and inclinations compared to
measured slopes in IRS spectra
of Taurus stars
Consistent with 1-0.1% depletion
Depletion of upper layers: zupp/zst
 = 0.001
=1
Furlan et al 2005