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. van Zadelhoff 2002 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 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

Mapping evolutionary paths? Evolutionary sequence: cTTs wTTs Debris  is the slope of the IR excess, t-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)

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

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 M. Simon et al. 2001, PdBI The CO line shape is Sensitive to: R disk, M star, Inc. These can be measured w/resolved images: Dent et al. 2005, JCMT v LSR (km/s) T MB (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

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

Blue: Canonical Model (Calvet et al. 2002, Qi et al ) Black: SMA data CO 2-1CO 3-2 Temperature Contour Tau=1 Surfaces CO 3-2 CO 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  ´´

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. R hot (KI) < R(CO) < R dust (SED) Good, h CO ≥ eV to dissociate.