1. Ge/Ay133 SED studies of disk “lifetimes” &
Long wavelength studies of disks
Ge/Ay133

2. 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!

3. 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.

4. 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

5. Disk Timescales 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?
Big RED circle: has disk
Padgett et al., 2006; Cieza et al., 2006

6. That is, are there multiple paths from optically thick to optically thin disks?
Class II
Class II
Disk
Star
Class II
Class III

7. Mapping evolutionary paths?
Evolutionary sequence: cTTs wTTs Debris
Gap opening
Grain growth
a is the
slope of
the IR
excess,
lt-o where
the star
and disk
contribute
equally to
the SED.

8. 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???

9. With modern mm-detectors, can sense beyond SED “knee”:
Can this long wavelength photometry help us understand disk
evolution and dissipation? (Images later)

10. Disk modeling of (sub)mm-wave flux measurements:
Measure, must know distance.
derive
Assume
UNLESS the
disk is spatially
resolved.

11. optically thin, near peak of blackbody:
optically thin, R-J limit

12. For “typical” assumptions, what do you find?
Current studies are flux limited at ~10 mJy:

13. 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.

14. So, we CAN measure many disk parameters, but only for a handful of sources for now. Use these results to guide continuum surveys:

15. Only substantial correlation is with overall SED and/or
accretion rate indicators, otherwise LARGE scatter!

16. 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).

17. 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).

18. Gas? CO/Good Dynamical, T Tracer
Dent et al. 2005,
JCMT
TMB (K)
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

19. With multiple CO lines T gradients:
M.R. Hogerheijde code
Qi et al. 2004, ApJ 616, L7.
TW Hya w/SMA

20. 13CO 2-1/TW Hya
Model
(Rout 110 AU)
Model
(Rout 172 AU)
Data

21. CO 2-1 CO 3-2 Temperature Contour
Only sensitive to disk surface layers, hard to get mass.
CO 2-1
CO 3-2
Temperature Contour
Tau=1 Surfaces
CO 3-2
CO 2-1
Blue: Canonical Model (Calvet et al. 2002, Qi et al )
Black: SMA data

22. 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

23. 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

24. Are there other examples? The case of LkHa 330.
1´´

25. 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…
Disk ages are difficult to determine, but chemistry may be useful in this respect. This figure is from a model of the sulfur chemistry in cores at ~50K. This may be similar to the outer regions of disks studied with OVRO. The dominant species migrates from H2S to SO,SO2 to CS over time. Here the timescale represents the time since the clock was reset, by an influx of H2S from grain surfaces. In the case of disks, this can give us a rough idea of the time since a major reprocessing of the grains. Toward LkCa 15 we observed large amounts of CS, including the isotope, C34S (1/20 CS), but no SO,SO2,H2S or OCS were detected. This indicates that the disk is reasonably old and has been quiescent for a long time, which is consistent with its age ~10Myr and grain chemistry.
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 ≥ eV to dissociate.