Ge/Ay133

SED studies of disk “lifetimes” & Long wavelength studies of disks

Characterizing large disk samples? SED Models:

IR disk surface within several 0.1 – several tens of AU(sub)mm disk surface at large radii, disk interior. Details next!

G.J. vanZadelhoff2002

Chiang &Goldreich 1997

HH 30

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 m.

Disk Fraction Correlations

Cieza et al. 2006

For wTTs sample projected on clouds, disk fraction increases with H Equivalent Width (EW), declines with age.

wTTs

cTTs

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?

Padgett et al., 2006; Cieza et al., 2006

Big RED circle: has disk

Class III

That is, are there multiple paths from optically thick to optically thin disks?

Class II Star

Disk

Class II

Class II

Mapping evolutionary paths?

• Evolutionary sequence: cTTs wTTs Debris

is theslope ofthe IRexcess,t-o wherethe starand diskcontributeequally tothe 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)

)( )( rrTRr do Measure, must know distance.

derive

AssumeUNLESS thedisk is spatiallyresolved.

Disk modeling of (sub)mm-wave flux measurements:

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

M. Simon et al. 2001, PdBI

The CO line shape isSensitive to:Rdisk ,Mstar, Inc.

These can bemeasured w/resolved images:

Dent et al. 2005, JCMT

vLSR (km/s)

TM

B (K

)

CO 3-2

With multiple CO lines T gradients:

Qi et al. 2004, ApJ 616, L7.TW Hya w/SMA

M.R. Hogerheijde code

13CO 2-1/TW HyaData

Model (Rout 110 AU)

Model (Rout 172 AU)

Blue: Canonical Model (Calvet et al. 2002, Qi et al. 2004 )Black: SMA data

CO 2-1 CO 3-2Temperature Contour

Tau=1 Surfaces

CO 3-2CO 2-1

Only sensitive to disk surface layers, hard to get mass.

Calvet et al. 2005, ApJ, 630, L185

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?

Are there other examples? The case of LkH 330.

1´´

For dust sublimation alone, the lines from T Tauri disks should be broader than those from Herbig Ae stars+disks. Often observed, but…

CO v =1-0 Emission from Transitional Disks?

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, hCO ≥ 11.09 eV to dissociate.