observations of disks around young stellar objects
DESCRIPTION
Observations of Disks around Young Stellar Objects. G. Duch êne & F. Ménard (Obs. Grenoble). Goals of this talk. Consider as wide a range of datasets as possible in 30 minutes! Will skip some very exciting aspects Discussion of selected physical aspects Leave out gas and chemistry - PowerPoint PPT PresentationTRANSCRIPT
Observations of Disks around Young Stellar Objects
G. Duchêne & F. Ménard (Obs. Grenoble)
G. Duchêne - Structure Formation in the Universe - May 2007
Goals of this talk
Consider as wide a range of datasets as possible in 30 minutes! Will skip some very exciting aspects
Discussion of selected physical aspects Leave out gas and chemistry
Persuade you that we can now constrain some physical processes Yet many open questions remain…
G. Duchêne - Structure Formation in the Universe - May 2007
Outline
General motivation Observational methods Disks in the context of star formation Disks in the context of planet formation Debris disks: after planets formed Summary and perspectives
G. Duchêne - Structure Formation in the Universe - May 2007
General MotivationGeneral Motivation
G. Duchêne - Structure Formation in the Universe - May 2007
Why do we care about disks?
A natural outcome ofstar formation
G. Duchêne - Structure Formation in the Universe - May 2007
Why do we care about disks?
A natural outcome ofstar formation
Planetary systemfactories
G. Duchêne - Structure Formation in the Universe - May 2007
Expected physical processes (I)
Influence of central star/environment Disk lifetime Total mass reservoir Overall structure
Disk dispersal mechanism Viscous dissipation of angular momentum Photo-ionization Dynamical dispersal (companion)
G. Duchêne - Structure Formation in the Universe - May 2007
Expected physical processes (II)
Substructure formation Spiral arms (instabilities, planets) Gap openings (planets)
Dust evolution Grain growth Radial migration Vertical sedimentation Change in grain structure
G. Duchêne - Structure Formation in the Universe - May 2007
Observations of disksObservations of disks
G. Duchêne - Structure Formation in the Universe - May 2007
Unresolved datasets: SEDs
The simplest approach: gather the energy and try to invert to disk structure Flared disks in most cases
Chiang & Goldreich (1997) Dullemond et al. (2007)
FlatFlared
G. Duchêne - Structure Formation in the Universe - May 2007
Unresolved datasets: SEDs
Useful approach for statistical purposes Can be dangerous on an object-to-
object basis Need for resolved datasets!
Burrows et al. (1996)
D’Alessio et al. (2001)
All TaurusCTTS
G. Duchêne - Structure Formation in the Universe - May 2007
Resolved datasets
A single image provides key parameters: Outer radius, position angle Inclination (sometimes) Optical depth (sometimes)
Bertout et al. (1998)
Guilloteau et al. (1999)
Not a normaldisk
G. Duchêne - Structure Formation in the Universe - May 2007
Resolved datasets
VLT/VISIR
SpitzerInterf.
All probe different dust populationsmass
grain size
structure
composition
G. Duchêne - Structure Formation in the Universe - May 2007
Resolved datasets
Need for complementary complex RT models
VLT/VISIR
SpitzerInterf.
G. Duchêne - Structure Formation in the Universe - May 2007
Disks and Star FormationDisks and Star Formation
G. Duchêne - Structure Formation in the Universe - May 2007
Disks and central object mass
How universal is star formation? Probe disk presence through IR excess
Overall fraction up to 90% (in Oph) Best studied population: the ONC
disks at all masses (0.1 - 5 M)
Hillenbrand et al. (1998)
Slight deficit atlow mass end?
G. Duchêne - Structure Formation in the Universe - May 2007
Disks and central object mass
Detection is harder around VLMS/BD because of cooler Teff
BDs: 40-75% up to ~5 Myr at least No substantial difference with stars
Liu et al. (2003)Jayawardhana et al. (2003)
G. Duchêne - Structure Formation in the Universe - May 2007
Disks and central object mass
Not only is disk frequency independent of mass, their structure is, too! Hydrostatic (flared) passive disks
Glauser et al. (2007) McCabe et al. (2007) Perrin et al. (2007)
~0.1 M ~0.5 M ~2 M
PDS 144HK TauIRAS 04158+2805
G. Duchêne - Structure Formation in the Universe - May 2007
Disks and central object mass
The special case of high-mass stars: Aligned (rotating) methanol masers, but not
so clear Norris et al. (1993), De Buizer et al. (2003)
Wide-angle outflows A huge ‘silhouette disk’ Difficult to conclude yet
Too far away Evolving too fast
Chini et al. (2004)
M17
20000 AU
G. Duchêne - Structure Formation in the Universe - May 2007
Disks and orientation of stars
Taurus molecular cloud = series of filaments orthogonal to B field
So are individual pre-stellar cores
Hartmann (2002)CO map Prestellar cores
G. Duchêne - Structure Formation in the Universe - May 2007
Disks and orientation of stars
Disks around T Tauri stars indicate the system’s symmetry axis Systems are randomly oriented w.r.t. local
magnetic field What happened?
Non-magnetic collapse?
Ménard & Duchêne (2004)
G. Duchêne - Structure Formation in the Universe - May 2007
Disks and Planet FormationDisks and Planet Formation(overall disk properties) (overall disk properties)
G. Duchêne - Structure Formation in the Universe - May 2007
Disks sizes and masses
Typical disk size ~ 200 AU Compares well with Solar System
Large scatter around median value!
Glauser et al. (2007)Stapelfeldt et al. (2003)
Kitamura et al. (2002)
HV TauIRAS 04158+2805
~ 40 AU
~ 1100 AU
G. Duchêne - Structure Formation in the Universe - May 2007
Disks sizes and masses
Disk masses can be derived from thermal radio fluxes/maps Uncertain dust opacities Uncertain gas/dust ratio
Derived total masses: Consistent with MMSN Consistent with stability
Natta et al. (2000)
G. Duchêne - Structure Formation in the Universe - May 2007
Disks sizes and masses
Radio interferometers (IRAM, OVRO) can resolve disks Typical surface density ~1 g.cm-3 @ 100AU Power law indices
– Temperature law– Surface density
‘Flat’ MMSN-like disks Good for planets! But interpolation…
Dutrey et al. (1996)
G. Duchêne - Structure Formation in the Universe - May 2007
Disk asymmetries: large scales
Evidence for dynamical perturbation: Companion, planet, high-mass disk? What you see is NOT what you have…
Grady et al. (2001) Fukagawa et al. (2004)Piétu et al. (2005)
AB AurHD 100546
Optically thin!
G. Duchêne - Structure Formation in the Universe - May 2007
Disk asymmetries: gaps
Planets embedded in disks open ‘gaps’ Can these be observed?
Gap size < 1AU High resolution + high contrast ALMA? New generation AO?
Remember, however: Spatial resolution remains an issue Gaps may be partly filled in
G. Duchêne - Structure Formation in the Universe - May 2007
Disk dissipation
Using disk counts in independent SFRs provides survival time of inner disk Essentially nothing left after 10 Myr
No environment effect OB vs T associations,
clusters Large bodies may still
be present and hiddenMeyer et al. (2000)
Disk lifetime
G. Duchêne - Structure Formation in the Universe - May 2007
Disk dissipation
Does disk dissipation depend on central object mass? Spitzer surveys of UpSco (~5Myr)
– G-B: 5 +/- 2 %– K0-M5: 19 +/- 3%– BDs: 37 +/- 9 %
Disk lifetime is longer for lower mass objects Because of slower viscous timescale?
Carpenter et al. (2005)
Scholtz et al. (2007)
}
G. Duchêne - Structure Formation in the Universe - May 2007
Inner disk dispersal
Disks disappear after inner hole clearing Evidence shows that disks dissipate
inside-out in <105 yrs (viscous timescale)
McCabe et al. (2006)D’Alessio et al. (2005)
0.2-
0.5
AU
mat
eria
l
0.5-2 AU material
Very fewtransition objectsCoKu Tau 4
G. Duchêne - Structure Formation in the Universe - May 2007
Inner disk dispersal
How long does the outer disk remain? Spitzer searches for disk with only outer
disk material (>5-10 AU) Only a few percent of such objects
Outer disk falls belowdetection threshold in <~ 105 yrs
Too fast for viscosity?
Padgett et al. (2006)
G. Duchêne - Structure Formation in the Universe - May 2007
Disks and Planet FormationDisks and Planet Formation(dust properties) (dust properties)
G. Duchêne - Structure Formation in the Universe - May 2007
Grain growth: mm view
First approach: SED slope (mm regime) Typically, amax ~ few mm to few cm
Natta et al. (2007)D’Alessio et al. (2001)
Smallgrains
Largegrains
Observeddistributionof spectral
indices
G. Duchêne - Structure Formation in the Universe - May 2007
Grain growth: silicates view
Silicate feature is size-dependent Small (< 0.1 m) vs large grains (~1 m) Larger grains do not contribute
Crystallinity produces sharp features
Kessler-Silacci et al. (2006)
G. Duchêne - Structure Formation in the Universe - May 2007
Grain growth: silicates view
Clear evolutionary sequence Larger grains come together with higher
grain crystallinity (above a threshold)
Kessler-Silacci et al. (2006) Van Boekel et al. (2005)
Hig
her
crys
talli
nity
Smaller grains
G. Duchêne - Structure Formation in the Universe - May 2007
Grain growth: scattered light
Stellar photons can scatter off dust grains at the disk surface Phenomenon depends on /a Larger grains scatter preferentially forward,
with a lower polarization rate Images and polarization maps can be
used to infer grain sizes Up to amax ~ few m typically
Advantage: longer probes deeper!!
G. Duchêne - Structure Formation in the Universe - May 2007
Grain growth: scattered light
Single power law size distribution Increasingly more isotropic scattering
HK Tau images (increasingly ‘peakier’) reveal larger grains inside (up to 3-5 m)
McCabe et al. (2003)McCabe et al. (in prep)
2.2 m 3.8 m 4.7 m 11.3 m
VLT/AO Keck/AO Keck/AO Keck
G. Duchêne - Structure Formation in the Universe - May 2007
Grain growth: the big picture
Each aspect probes A different region of disks Different grain sizes/populations
In each case, analysis requires knowledge of additional information (radius, inclination, …)
Ideally, comparison all datasets to a single (complex) radiative transfer model
G. Duchêne - Structure Formation in the Universe - May 2007
Vertical sedimentation
If large grains disappear from the surface, thermal equilibrium is changed Change in disk SED
Difficult to ascertain, however
Dullemond & Dominik et al. (2004)
Sedimentation mimics a flat disk
G. Duchêne - Structure Formation in the Universe - May 2007
Vertical sedimentation
Confront mm regime and silicates Can be convincing (if composition is well
distributed throughout the disk)
Pinte et al. (in prep)
IM Lup
Small grainsonly
Small andlarge grains
G. Duchêne - Structure Formation in the Universe - May 2007
Vertical sedimentation
Confront mm regime and silicates Can be convincing (if composition is well
distributed throughout the disk)
Pinte et al. (in prep)
IM Lup
Small grainsonly
Small andlarge grains
Small andlarge grains
sedimentation
G. Duchêne - Structure Formation in the Universe - May 2007
Radial migration
Interferometry + spectroscopy (MIDI) Silicate features a few AU from the star Higher crystallinity!
Grain processing?
van Boekel et al. (2004)
Shegerer et al. (subm.)
RY Tau (K1)
small
crystalline
G. Duchêne - Structure Formation in the Universe - May 2007
Radial migration
Difficult to quantify differentiation Many assumptions in analysis
Nonetheless, there is evidence that grain properties depend on radial distance to the star
However, we cannot prove that grains have migrated! Crystallinization may be a local processing
G. Duchêne - Structure Formation in the Universe - May 2007
Further in time: debris disksFurther in time: debris disks
G. Duchêne - Structure Formation in the Universe - May 2007
Debris disks: basics
Debris disks are the final stage in planet formation before zodiacal disks Formed through collisions of solid bodies
They are optically thin Easier to interpret Harder to observe
SED is usually limited Rough constraints only
Beichman et al. (2006)
G. Duchêne - Structure Formation in the Universe - May 2007
Debris disks: porosity, aggregates With many independent observables,
finer models can be tested The AU Mic debris disk is made of (small)
porous grains
Fitzgerald et al. (2007)
porous
compact
G. Duchêne - Structure Formation in the Universe - May 2007
Debris disks: porosity, aggregates Another debris disk: HD 181327 All observables cannot be explained
simultaneously with spherical grains Aggregates?
Schneider et al. (2006)
vs?
SED
Phasefunction
G. Duchêne - Structure Formation in the Universe - May 2007
Summary and PerspectivesSummary and Perspectives
G. Duchêne - Structure Formation in the Universe - May 2007
Summary
We have access to many types of complementary observations
Several physical processes can be (somewhat) constrained Core collapse/fragmentation Disk dissipation and inner hole clearing Grain growth Dust settling Presence of planetesimals
G. Duchêne - Structure Formation in the Universe - May 2007
Perspectives
More observations will come with future instrumentation (e.g., ALMA)
At this stage, we still need Complex modeling/analysis of datasets More multi-technique analysis Tests of the basic processes in models
Wait for next talks, to get the theorists’ point of view!