Transcript lec09_14oct2011

SED studies of disk “lifetimes” &
Long wavelength studies of disks
Ge/Ay133
Characterizing large disk samples? SED Models:
HH 30
G.J. van
Zadelhoff
2002
Chiang &
Goldreich
1997
IR
disk surface within several 0.1 – several tens of AU
(sub)mm
disk surface at large radii, disk interior.
Details next!
Use SED surveys
to probe disk
evolution w/time,
accretion rate, etc.
Find very few objects
with moderate IR
excesses, most disk
systems are optically
thick out to 24 mm.
Disk Fraction Correlations
cTTs
wTTs
For wTTs sample projected on clouds, disk fraction increases with
Ha Equivalent Width (EW), declines with age.
Cieza et al. 2006
Disk Timescales
Big RED circle: has disk
Some wTTs do have disks,
not seen before w/IRAS.
But, only the young ones
(age < 3 to 6 MYr)
The ages are uncertain due
to models, but ~half the
young wTTs lack disks
(even at 0.8 to 1.5 Myr).
Thus, time is NOT the only
variable. How might disks
evolve?
Padgett et al., 2006; Cieza et al., 2006
That is, are there multiple paths from
optically thick to optically thin disks?
Disk
Class II
Class II
Star
Class II
Class III
Mapping evolutionary paths?
• Evolutionary sequence: cTTs
wTTs
Debris
a is the
slope of
the IR
excess,
lt-o where
the star
and disk
contribute
equally to
the SED.
Statistically, how long do dust grains in disks “survive”?
Basic result:
Disks dissipate
within a few
Myr, but with
a large disp.
for any SINGLE
system. When
they go, however,
the dissipation
is FAST in
comparison w/
disk “lifetime.”
Gas???
With modern mm-detectors, can sense beyond SED “knee”:
Can this long wavelength photometry help us understand disk
evolution and dissipation? (Images later)
Disk modeling of (sub)mm-wave flux measurements:
Measure, must know distance.
derive
Assume
UNLESS the
disk is spatially
resolved.
ro Rd T (r ) (r )
optically thin, near peak of blackbody:
optically thin, R-J limit
0
For “typical” assumptions,
what do you find?
Current studies are flux
limited at ~10 mJy:
Submm Continuum Imaging – TW Hya
• The SMA continuum measurements agree well with the
predictions of the physically self-consistent irradiated
accretion disk model for TW Hya (Calvet et al. 2002)
• The radial brightness distribution of the disk observed at
345 GHz is also consistent with the Calvet model.
So, we CAN measure many disk parameters, but only for a handful
of sources for now. Use these results to guide continuum surveys:
Only substantial correlation is with overall SED and/or
accretion rate indicators, otherwise LARGE scatter!
Other “factoids”:
Submm flux highly
correlated with
the presence or
absence of IR
excess. Almost no
disks w/weak IR
but strong submm.
Very little dependence
of MAXIMUM disk
mass on age (that is,
some fairly OLD stars
have >MMSN disks).
Other “factoids”:
Submm flux highly
correlated with
the presence or
absence of IR
excess. Almost no
disks w/weak IR
but strong submm.
Very little dependence
of MAXIMUM disk
mass on age (that is,
some fairly OLD stars
have >MMSN disks).
Gas?
CO/Good Dynamical, T Tracer
TMB (K)
Dent et al. 2005,
JCMT
vLSR (km/s)
The CO line shape is
Sensitive to:
Rdisk ,Mstar, Inc.
These can be
measured
w/resolved images:
M. Simon et al.
2001, PdBI
With multiple CO lines
CO 3-2
M.R. Hogerheijde code
TW Hya w/SMA
Qi et al. 2004,
ApJ 616, L7.
T gradients:
13CO
2-1/TW Hya
Data
Model
(Rout 110 AU)
Model
(Rout 172 AU)
Only sensitive to disk surface layers, hard to get mass.
CO 2-1Temperature ContourCO 3-2
Tau=1 Surfaces
CO 3-2
CO 2-1
Blue: Canonical Model (Calvet et al. 2002, Qi et al. 2004 )
Black: SMA data
Also, very few
“transitional”
disks are found
(that is, disks w/
inner holes):
Statistics are ~a
few of many
hundreds of
young stars.
Calvet et al. 2005, ApJ, 630, L185
At least some disks
evolve “from the
inside out.” Does
this apply more
generally, or can
disks dissipate in
a variety of ways?
Calvet et al. 2005, ApJ, 630, L185
Are there other examples? The case of LkHa 330.
1´´
CO v =1-0 Emission from Transitional Disks?
For dust sublimation
alone, the lines from T
Tauri disks should be
broader than those from
Herbig Ae stars+disks.
Often observed, but…
The TW Hya lines are extremely
narrow, with i~7°
R≥0.37 AU.
Similar for SR 9, DoAr 44, GM Aur.
Rhot(KI) < R(CO) < Rdust(SED)
Good, hnCO ≥ 11.09 eV to dissociate.