Ge/Ay133
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Transcript of Ge/Ay133
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Ge/Ay133
SED studies of disk “lifetimes” & Long wavelength studies of disks
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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
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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.
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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
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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
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Class III
That is, are there multiple paths from optically thick to optically thin disks?
Class II Star
Disk
Class II
Class II
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Mapping evolutionary paths?
• Evolutionary sequence: cTTs wTTs Debris
is theslope ofthe IRexcess,t-o wherethe starand diskcontributeequally tothe SED.
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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???
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With modern mm-detectors, can sense beyond SED “knee”:
Can this long wavelength photometry help us understand disk evolution and dissipation? (Images later)
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)( )( rrTRr do Measure, must know distance.
derive
AssumeUNLESS thedisk is spatiallyresolved.
Disk modeling of (sub)mm-wave flux measurements:
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optically thin, near peak of blackbody:
optically thin, R-J limit
0
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For “typical” assumptions, what do you find?
Current studies are flux limited at ~10 mJy:
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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.
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So, we CAN measure many disk parameters, but only for a handful of sources for now. Use these results to guide continuum surveys:
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Only substantial correlation is with overall SED and/or accretion rate indicators, otherwise LARGE scatter!
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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).
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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).
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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
)
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CO 3-2
With multiple CO lines T gradients:
Qi et al. 2004, ApJ 616, L7.TW Hya w/SMA
M.R. Hogerheijde code
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13CO 2-1/TW HyaData
Model (Rout 110 AU)
Model (Rout 172 AU)
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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.
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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.
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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?
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Are there other examples? The case of LkH 330.
1´´
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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.