Star and Planet Formation

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Star and Planet Formation

• Neal Evans
• The University of Texas at Austin

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Star Formation in Galaxies
Antennae galaxy merger. Visible (HST) shows
copious star formation, but misses the main show.
Most intense star formation in obscured region
traced by CO.
CO(1-0) OVRO
Whitmore et al. (1999) Wilson et al. (2000)
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New Views are Coming
The Archive is open http//ssc.spitzer.caltech.ed
u/
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Star Formation/Galaxy Formation

• Key part of galaxy formation
• Properties of molecular clouds in other galaxies
• Connect studies of distant galaxies to MW
• Collective, clustered, massive SF
• Molecular line probes of high density
• Dust continuum emission
• Insights into high-z starbursts

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Star Formation traced by HCN
Relation between LIR and LCO becomes non-linear
for very high LIR. Stays linear for LHCN.
J. Wu et al. Data from Gao and Solomon 2003.
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Relation Same for Cores in MW
LHCN or LCS for cores in MW also linear with
LIR. (For LIR gt 104 Lsun) These points are for
HCN 3-2 and CS 5-4. Same line as HCN 3-2 in
galaxies. Parallel to HCN 1-0 relation for
starbursts. Checking HCN 1-0 in MW.
J Wu et al. In prep.
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What probes can we use?

• Dust
• Extinction of background stars
• Probe Nd(b), Bperp
• Emission in infrared to millimeter
• Probe Td( r), Nd(b), Bperp
• Problem need to know dust properties
• Molecules
• Emission or absorption (infrared to radio)
• Probe TK( r), n( r), v( r), Bpar
• Problem chemistry

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Studies of High Mass Regions

• Many Detailed Studies
• Ho, Zhang,
• Surveys
• van der Tak et al. (2000) (14 sources)
• Beuther et al. (2002) (69 sources)
• Survey of water masers for CS
• CS survey Plume et al. (1991, 1997)
• Dense ltlog ngt 5.9
• Maps of 51 in 350 micron dust emission
• Mueller et al. 2002
• Maps of 63 in CS J 54 emission
• Shirley et al. 2003

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Luminosity versus Mass
Log Luminosity vs. Log M red line masses of
dense cores from dust Log L 1.9 log M blue
line masses of GMCs from CO Log L 0.6 log
M L/M much higher for dense cores than for whole
GMCs.
Mueller et al. (2002)
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Linewidth versus Size
Correlation is weak. Linewidths are 4-5 times
larger than in samples of lower mass
cores. Massive clusters form in regions of high
turbulence, pressure.
Shirley et al. 2003
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Cumulative Mass Function
Incomplete below 103 Msun. Fit to higher mass
bins gives slope of about 0.93. Steeper than
that of CO clouds or clumps (0.5 on this
plot). Similar to that of clusters, associations
(Massey et al. 1995) in our Galaxy and in
Antennae (Fall et al. 2004).
Shirley et al. 2003
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Massive Cores Gross Properties

• Massive, Dense, Turbulent
• Mass distribution closer to clusters, stars than
  GMC
• Much more turbulent than low mass cores
• A model for starbursts?
• Luminosity correlates well with core mass
• Less scatter than for GMCs as a whole
• L/M much higher than for GMCs as a whole
• L/Mdust 1.4 x 104 Lsun/Msun high-z starbursts
• L/L(HCN) similar to starbursts
• Starburst all gas like dense cores?

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Hints of Dynamics
A significant fraction of the massive core sample
show self-reversed, blue-skewed line profiles in
lines of HCN 3-2. Of 18 double-peaked profiles,
11 are blue, 3 are red. Suggests inflow motions
of overall core. Vin 1 to 4 km/s over radii of
0.3 to 1.5 pc.
J. Wu et al. (2003)
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Open Questions for ALMA

• Studies of gas, dust, high n tracers in galaxies
• Detailed structure of massive cores
• Can we separate into fragments/clusters?
• Simulations predicting properties
• Understand IMF?
• See SMA early results as preview for ALMA
• Can we study dynamics?
• Test inward motion hints in single-dish spectra
• Separate dynamics of fragments
• Evolution of dust, ice, gas-phase chemistry
• Combine ALMA with Spitzer, SOFIA, Herschel,

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Links to DRSP

• Gas fraction/Star formation in Galaxies
• CO maps w High Res. (e.g., 1.7.6)
• COgas conversion (e.g., 1.7.3, 1.7.11)
• High nc tracers (e.g., 1.7.1, 1.7.9)
• Dust (e.g., 1.7.10 and others with lines)
• Need more on tracers of dense gas?

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Links to DRSP

• Structure of massive cores
• Tracers of n, T (e.g., 2.1.4)
• Dynamics
• Chemistry (e.g., 2.3.15)
• More thought on resolving fragmentation?

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What do we need?

• High resolution
• High dynamic range, image fidelity
• Bright, but complex, sources
• Flexible correlator
• Very rich spectrum, need many diagnostics
• Full complement of receivers
• For exgal clouds, excellent sensitivity

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Low Mass vs. High Mass

• Low Mass star formation
• Isolated (time to form lt time to interact)
• Low turbulence (less than thermal support)
• Nearby ( 100 pc)
• High Mass star formation
• Clustered
• Time to form may exceed time to interact
• Turbulence gtgt thermal
• More distant (gt400 pc)

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High vs. Low Early Conditions
Property Low High
p 1.8 1.8
nf (median) 2 x 105 1.5 x 107
Linewidth 0.37 5.8
n( r) nf (r/rf)p rf 1000 AU
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Even Isolated SF Clusters
Taurus Molecular Cloud Prototypical region of
Isolated star formation
Myers 1987
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But Not Nearly as Much

• Orion Nebula Cluster
• gt1000 stars
• 2MASS image

1 pc
Taurus Cloud at same scale 4 dense cores, 4
obscured stars 15 T Tauri stars
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The Basic Features
Envelope Disk Protostar Jet/wind/outflow
T. Greene
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Studies of the Envelope

• All quantities vary along line of sight
• Dust temperature, Td( r)
• Heating from outside, later inside
• Gas temperature, TK( r)
• Gas-dust collisions, CRs, PE heating
• Density, n(r), predicted to vary
• Velocity, v(r), connected to density
• Abundance, X(r), varies
• Photodissociation, freeze-out, desorption

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An Evolutionary Model

• A physical model from theory
• Sequence of Bonnor-Ebert spheres of increasing nc
• e.g., Shu (1977) Inside-out collapse
• Calculate luminosity of central stardisk
• Dust temperature through envelope
• Gas temperature
• Chemical abundances
• Follow gas as it falls, using evolving conditions
• Line Profiles including all effects

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Theory gives n(r,t), v(r,t)
tlt0 Series of Bonnor-Ebert spheres tgt0
Inside-out collapse model (Shu 1977)
C. Young
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L(t) from Accretion, Contraction
L(t) calculated. First accretion. First onto
large (5 AU) surface (first hydrostatic core).
Then onto PMS star with R 3 Rsun, after
20,000 to 50,000 yr. And onto disk.
Prescriptions from Adams and Shu. Contraction
luminosity and deuterium burning dominates after
t 100,000 yr.
C. Young and Evans, in prep.
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Evolution of Dust Tracers
Assumes distance of 140 pc and typical telescope
properties.
C. Young and Evans, in prep.
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Calculate Gas Temperature
Use gas energetics code (Doty) with gas-dust
collisions, cosmic rays, photoelectric heating,
gas cooling. Calculate TK( r, t).
C. Young and J. Lee et al.
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Calculate Abundances
Chemical code by E. Bergin 198 time steps of
varying length, depending on need. Medium sized
network with 80 species, 800 reactions. Follows
512 gas parcels. Includes freeze-out onto grains
and desorption due to thermal, CR, photo effects.
No reactions on grains. Assume binding energy on
silicates for this case.
J. Lee et al. In prep
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Calculate Line Profiles
Line profiles calculated from Monte Carlo plus
virtual telescope codes. Includes collisional
excitation, trapping. Variations in density,
temperature, abundance, velocity are
included. Assumes distance of 140 pc and typical
telescope properties.
J. Lee et al. In prep
J. Lee et al. In prep
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A Closer Look
Lines of HCN (J 10). Shown for four times.
Top plot with 50 resolution. Bottom plot with
5 resolution. ALMA will probe the desorption
wave.
J. Lee et al. In prep
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Evidence for Infall
Good evidence in a few. (e.g., Zhou et al.
1993) Surveys indicate infall is common at
early stages. Gregersen et al. 1997,
2000 Mardones et al. 1997
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Observing Infall with ALMA

• A key observation is to observe the infalling gas
  in redshifted absorption against the background
  protostar
• Very high spectral resolution (lt0.1 km/s) is
  required
• High sensitivity to observe in absorption against
  disk.

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Low Mass Cores Gross Properties

• Molecular cloud necessary, not sufficient
• High density (ngt104 cm3)
• Low turbulence
• Centrally peaked density distribution
• Power law slope high mass
• Fiducial density 100 times lower
• Complex chemistry, dynamics even in 1D
• Evidence for infall seen, but hard to study
• Outflow starts early, strong effect on lines
• Rotation on small scales

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Open Questions

• Initial conditions
• Cloud/core interaction
• Trace conditions in core closer to center
• Inward motions before point source?
• Timescales for stages
• Establish existence and nature of infall
• Inverse P-Cygni profiles against disks
• Chemo-dynamical studies
• Envelope-Disk transition
• Inner flow in envelope
• Outflow dynamics
• Nature of interaction with ambient medium

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Links to DRSP

• Initial Conditions
• Cloud/core relation (e.g., 2.1.6, 2.2.1)
• Conditions in cores (e.g., 2.1.2, 2.1.7, 2.2.24)
• Inward motions (e.g., 2.1.8, 2.2.3)
• Timescales (need big sample)
• Infall
• Inverse P-Cygni (2.2.4)
• Chemo-dynamical (2.3.2, 2.3.8)
• Envelope-disk interaction (e.g., 2.1.7)
• Outflow dynamics (e.g., 2.2.10, 2.3.8)

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Sub-stellar Objects

• Brown dwarfs, free-floating planets,
• BDs clearly exist, clearly have disks,
  accretion,
• How do these form?
• Ejection from multiples, clusters
• Formation like stars
• Properties of disks
• Do they form in low-mass, dense envelopes?
• Low end of core mass function

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Links to DRSP

• Evidence for envelopes/disks
• Surveys for cores to low levels (e.g., 2.1.1,
  2.1.6)
• Study of disks around known substellar objects
  (e.g., 2.4.4)
• Some more thought needed?

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Planet Formation

• Best studied around isolated stars
• Origin and evolution of disk
• Gaps, rings,
• Debris disks as tracers of planet formation
• Chemistry in disks
• Evolution of dust, ices, gas

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Planet Formation
SMM image of Vega shows dust peaks off center
from star (). Fits a model with a Neptune like
planet clearing a gap. This is with 15-m at 850
microns and 15 resolution. ALMA can do at
higher resolution.
SMM image of Vega JACH, Holland et al.
Model by Wyatt (2003), ApJ, 598, 1321
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With higher resolution
Vega also observed by Wilner et al. (2003). Model
of resonance with planet.
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Predicts motion of dust
Model and Animation by Marc Kuchner
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ALMA Resolution
Simulation Contains 140 AU disk inner hole
(3 AU) gap 6-8 AU forming giant planets at
9, 22, 46 AU with local over-densities ALMA
with 2x over-density ALMA with 20
under-density Each letter 4 AU wide, 35 AU
high Observed with 10 km array At 140 pc, 1.3 mm
Observed Model
L. G. Mundy
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Chemistry of Planet-forming Disks
LkCa15 with OVRO. Trace the composition changes
with evolution. ALMA will have resolution and
sensitivity to do this kind of study in many
disks.
Qi et al. 2004
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The Icy Component
Rich spectrum of ices CO2, H2O, CH3OH, OCN and
others. Can study ice evolution in regions
forming sun-like stars. Little processing at Tgt50
K, some evidence for lower temperature processing.
Spitzer IRS plus Keck/NIRSPEC or VLT/ISAAC
Boogert et al. ApJS, submitted
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Open Questions

• How the disk initially forms
• Timescales for disk evolution
• How planets form in the disk
• Core accretion or Gravitational Instability
• How unusual the solar system is
• Systems with giant planets out where ours are
• Evolution of dust, ice, gas in disk
• Building blocks for planets

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Links to DRSP

• Formation of disk (e.g., 2.1.7)
• Timescales (e.g., 2.4.6, 2.4.7)
• Planet formation (e.g., 2.4.3, 2.4.5)
• Planetary systems like ours?
• Chemistry in disks (e.g., 2.4.2)

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Requirements

• Maximum Spatial resolution
• Image fidelity (gaps will be hard to see)
• Best sensitivity
• Especially for debris disks
• Flexible correlator, receiver bands
• Chemistry

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In the ALMA era
SOFIA 2005
SMA, CARMA, eVLA, LMT, GBT, APEX, ASTE, JCMT,
CSO,
Spitzer 2003
Herschel 2007
SAFIR 2015
JWST 2011
AT-25 2012
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Making the most of ALMA

• Complementary Observatories
• User-friendly system
• Low barriers to those from other wavelengths
• Proposals, planning tools, reduction, analysis
• Scientific support staff
• Broad wavelength experience
• Financial support tied to time

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A Closer Look
A few abundance profiles at t100,000
yr. Vertical offset for convenience (except CO
and HCN). Big effect is CO desorption, which
affects most other species. Secondary peaks
related to evaporation of other species.
J. Lee et al. In prep
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Bolocam map of Ophiuchus
Bolocam map (1.2 mm) of region in Spitzer survey.
Covers very large area (gt 10 sq. deg.) compared
to any previous map. Rms noise 50 mJy, with
about half the data.
K. Young et al. In prep
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Early Results from Spitzer

• Based on validation data (about 1)
• Observed two small cores (IRAC/MIPS)
• One (L1228) with a known infrared source
• One (L1014) without
• Observed a few IRS targets
• B5 IRS
• HH46/47 IRS (with ERO team)

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A Typical Starless Core
L1014 distance 200 pc, but somewhat uncertain.
R-band image from DSS
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A Surprise from Spitzer
Three Color Composite Blue 3.6 microns Green
8.0 microns Red 24 microns R-band image from
DSS at Lower left. We see many stars through the
cloud not seen in R. The central source is NOT a
background star. L1014 is not
source-less. Larger size in red is PSF.
C. Young et al. ApJS, submitted
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Source Peaks on mm Emission
Both long-wave maps are 3-sigma contours.
C. Young et al. ApJS, submitted
Left 8 micron on 1.2 mm MAMBO dust continuum
emission (Kauffmann Bertoldi) Right 24 micron
on 850 micron SCUBA data (Visser et al. 2002)
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Models
Model of SED for d 200 pc. Central object has
very low luminosity 0.09 Lsun. Requires BB plus
disk (red line) in an envelope. M(envelope) about
2 Msun. Cannot be a stellar-mass object with
significant accretion. Probably sub-stellar at
this point. Alternative model more distant (2.6
kpc) object lined up by chance with peak of a
foreground core (dashed line)
C. Young et al. ApJS, submitted
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Lessons from L1014

• Starless cores may not be
• Or may have substellar objects
• 1 out of 1 has a source (will soon have more)
• Very low luminosity sources may exist
• Must be low mass and low accretion
• Caveat possible background source

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HH46/H47 Cloud
NASA/JPL-Caltech