Download Beyond Orion: Exploring Star Formation at Radio Frequencies

Seeing Stars with
Radio Eyes
Christopher G. De Pree
RARE CATS
Green Bank, WV
June 2002
Overview
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Why study star formation?
Some unanswered questions in
star formation
Successes and limitations of
optical wavelength studies
Advantages of radio wavelength
studies
Recent discoveries in star
formation
Conclusions
Why study Star
Formation?
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We are made of star stuff
 Nucleosynthesis
creates elements
through iron (Fe)
 Supernovae create everything else
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The death and birth of stars may
be linked (triggered star formation)
Complex molecules can form on
dust grains near young stars
Young stars “stir up” clouds of gas
Why study Star
Formation (cont.)?
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Stars have a “life process”
 Star
Formation
 Stellar Evolution
 Supernovae, planetary nebulae
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Where there are stars, there are
planets
Effect on galactic evolution
 The Antennae
(Arp 224)
 Andromeda HST with CO (BIMA)
Giant
Molecular
Clouds
in
Andromeda
The Process of Star
Formation
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Collapsing molecular cloud core
Inside-out collapse produces a
protostar plus accretion disk
Bipolar molecular outflow carries
away angular momentum
What do we look for to see the
earliest stages?
 Dense
cloud cores
 Infalling molecular material
 Molecular disks/outflows
Jet Example: Core of
NGC 2071
Open questions in star
formation
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Do all stars form planets?
Are accretion disks common to all
star masses?
Do all young stars have outflows?
For how long?
Do massive stars (>5 solar mass)
form differently than low mass
stars?
Do massive star outflows “stir up”
molecular clouds?
Optical wavelength
studies
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Best for studying
Source of ionization (stars)
 Ionized gas (if unobscured, e.g. Orion)
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Potential problems
Star forming regions are often highly
obscured (e.g. NGC 253)
 The early stages of star formation are not
optically visible (radio, infrared)
 Molecular material (fuel tank) best
detected at radio frequencies
 Deeply embedded ionized material best
detected at radio frequencies
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Radio wavelength
studies (star formation)
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Molecular gas (the fuel tank)
 Molecular
clouds
 Protostellar disks
 Molecular outflows
 Complex molecules
Molecules and
Outflows
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Molecules in Orion
Distribution of molecules
Abundance of molecules
Source motions (rotations
and outflows)
Presence of complex
molecules
Potential for pre-life
chemistry
Viewing the
Milky Way
Galaxy
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90 cm image
A different view
Young stars
Dying stars
Magnetic fields
Ted LaRosa
(Kennesaw)
My Interests in this
Puzzle
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HII Regions (regions of ionized gas
around massive stars)
High resolution imaging of the
ionized gas
Kinematics (motions) of the ionized
gas
Understanding the earliest stages
of massive star formation
Radio wavelength
studies of HII Regions
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Obscured ionized gas
High density gas (young regions)
 Gas velocities (ionized outflows)
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Ionized shells at the centers of outflows
(e.g. G5.89 Observed with the VLA)
Disadvantage: resolution
Very Large Array (VLA)
 Berkeley Illinois Maryland Association
 Owens Valley Radio Observatory
 But: VLA at 7 mm—same resolution as
the Hubble Space Telescope
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Observing with the Very
Large Array
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W49
Observed
with the VLA
(2000)
W49A Star Forming
Region at 600 A.U.
Resolution (2002)
“Bipolar Outflow”
Spectral Lines/Bohr
Model of the Atom
“Imaging Spectroscopy”
Recent Discoveries
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Optical
 Extrasolar
planets (Doppler shift)
 Protoplanetary disks (Orion)
 Bipolar outflows (HH objects)
Recent Discoveries
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Radio
 Rotating
protoplanetary disks
 Ionized and molecular outflows
 High density regions
 Outflows may support clouds
What have we learned?
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Some HII regions are much smaller and
far brighter than previously thought
“Typical” HII regions were thought to be
~1 pc in diameter
“Typical ultracompact” HII regions that
we study are ~0.01 pc in diameter
These new sources are younger and
brighter—give us insight into an earlier
phase of star formation
Spectral line detections—we see rotation
and outflow in many sources
Conclusions
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Star formation studies tell us
about...
 Chemical
evolution of the universe
 Structure and evolution of galaxies
 Enrichment of the space between
the stars (the ISM)
 Abundance of elements
 Prevalence of planets
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Radio observations reveal...
 Embedded
protostars
 Rotating molecular disks
 Molecular outflows
 Complex organic molecules
Future developments
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The Millimeter Array (MMA)
 36
10-meter antennas
 Llano de Chajnantor, Chile
 Elevatation-16,400 feet
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VLA Upgrade (EVLA)
 Increased
resolution
 New correlator (spectral line &
sensitivity)
 Fully equipped at 7 mm