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The ALMA revolution: gas and dust in planet-forming disks
Nienke van der Marel Beatrice Watson Parrent fellow IfA Manoa, University of Hawaii
February 19th 2016
Star and planet formation
Figure M. Persson
A special class of disks...
Transitional disks
First discovery: Strom et al. 1989
Not necessarily an evolutionary term!
Transitional disks
Spitzer infrared observations
Pioneering millimeter interferometry (SMA, CARMA,PdBI)
HD135344B
LkCa15
Brown et al. 2007, 2009, Isella et al. 2010
Link with planet formation?
Cavity clearing mechanisms
● Grain growth
● Photoevaporation
● Companion
● Dead zones
trapping
trapping
Dust trapping
● FARGO model ● Gas density: planet clearing
Pinilla et al. 2012
Dust trapping
Pinilla et al. 2012
● FARGO model ● Gas density: planet clearing
Dust evolution
● Dust growth in a normal disk − Coagulation and fragmentation − Radial inward drift
● Dust can not grow beyond millimeter sizes?
● Two dust properties: − Large particles move
towards high pressure − Small particles move
with the gas => Pressure bump?
Pressure
headwind
Dust trapping
● Planet generates a radial pressure bump in gas
● Large dust will be trapped and no longer migrates inward
Pinilla et al. 2012
Dust trapping
Pinilla et al. 2012
Combination planet-disk interaction and dust evolution
Dust trapping
● Due to drag forces, larger dust moves towards high pressure: − density gradient
(planet) − viscosity gradient
(dead zone: low ionization)
Cavity clearing mechanisms
=> Need to know the gas and dust distribution inside cavity: ALMA
● Grain growth
● Photoevaporation
● Companion
● Dead zones
mm-dust gas
trapping
trapping
Before ALMA…
SMA 345 GHz
With ALMA…
ALMA Band 7
Other transition disks (ALMA)
Large variety of structures due to increased sensitivity & resolution
Van Dishoeck et al. 2015
ALMA Early Science
● Cycle 0: 2011-2012 ● ~16 antennas, up to 400 m baselines ● Target: Oph IRS 48
− d ~ 120 pc − 12CO 6-5 & C17O 6-5 − 690 GHz/0.44mm continuum − 0.25” resolution − Cavity size 60 AU (0.5”)
Geers et al. 2007
Oph IRS 48
Gas cavity: planet?
12CO observations: velocity map
Bruderer et al. 2014
Oph IRS 48ALMA B9: Millimeter asymmetry!
Van der Marel et al. 2013
Different distribution dust vs gas:
=> trapping!
Oph IRS 48
Millimeter-dust concentrated on one side of the disk
Micrometer-dust gathered in a ring-structure
Gas in a full disk witha small cavity (planet?)
What can cause this kind of structure? Van der Marel et al. 2013
Dust trapping
● What is the origin of the azimuthal asymmetry? ● Steep drop & low viscosity ⇒ pressure bump becomes Rossby unstable
Pinilla et al 2012 Birnstiel et al. 2013
Ataiee et al. 2013
Dust trapping
● What is the origin of the azimuthal asymmetry? ● Steep drop & low viscosity ⇒ pressure bump becomes Rossby unstable
long-lived vortex (moving on
Keplerian orbit)
Pinilla et al 2012 Birnstiel et al. 2013
Ataiee et al. 2013
Dust trapping
● Small gas asymmetry ⇔ large dust asymmetry
Birnstiel et al. 2013
mm-dust
gas/small grains
Subaru (SEEDS) and ALMA complementary
Follette et al. 2015
mm grains micron grains
Oph IRS 48
Subaru (SEEDS) and ALMA complementary
van der Marel et al. 2015 Thalmann et al. 2010 Muto et al. 2012 Mayama et al. 2012 Tsukagoshi et al. 2014 Canovas et al. 2016
Sz9
mm grains look very different from the micron grains!
Summary continuum emission
• Continuum emission shows rings and asymmetries
• The structures are consistent with trapping in pressure bumps
• So what about the gas?
Trapping: clearing by a planet
● Grain growth
● Photoevaporation
● Companion
● Dead zones
mm-dust gas
trapping
trapping
Gas structure: CO observations
Other transition disks (ALMA)● Band 9 continuum & 12CO 6-5 at 0.25”
Van der Marel et al. 2015a/Ch. 6
Other transition disks (ALMA)● Band 9 continuum & 12CO 6-5 at 0.25”
Van der Marel et al. 2015a
CO is present inside the dust cavities => but optically thick and difficult to analyze!
CO analysis
CO photodissociated
CO frozen out
Dutrey et al. 2014 Bruderer 2013
Disk structure: => Where does the CO emission originate?
DALI CO analysis
DALI
Bruderer et al. 2012, 2013, 2014
DALI CO analysis● Includes: freeze-out,
photodissociation, UV-field, chemical network, heating/cooling...
● Input: density gas and dust with drop inside cavity
Gas structure
● All five transition disks in this sample have − Dust density drop of at least
a factor 1000 − Gas inside the cavity − Gas density drop of a factor
10-100
Van der Marel et al. 2015a
Consistent with planet clearing + trapping scenario
CO isotopologues
Van der Marel et al. 2015c
CO isotopologues
Gas cavity < dust cavity in all cases studied to date
Van der Marel et al. 2015c
CO isotopologues
Gas cavity < dust cavity in all cases studied to date
Comparison models with data:
Van der Marel et al. 2015c
• Quantify gap depth/width: relation to planets?CO isotopologues
de Juan-Ovelar et al. 2013 Fung et al. 2014
Rcavgas__ Rcavdust
• Quantify gap depth/width: relation to planets?CO isotopologues
van der Marel et al. 2016
Using both relations: low viscosity and planet masses ~ few Jupiters
ALMA and Subaru complementary
Can Subaru detect the predicted planets (or set limits)?
CO isotopologues
● Gas cavities inside dust cavities ● trapping ● planet formation sites
● Is this true for all transition disks?
ESO 1549 (Kornmesser)
Summary
● Transitional disks are giant dust traps ● Dust growth visible through resolved α ● Quantification of gas densities in disks:
=> evidence for embedded planets • Higher spatial resolution
=> more complex structures
• What will ALMA reveal next?
?