Ge/Ay133 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 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

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

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.

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.

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

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 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

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

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

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. 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… 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 ≥ 11.09 eV to dissociate.