Seeing Stars with Radio Eyes
Christopher G. De PreeRARE CATSGreen Bank, WVJune 2002
Overview
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? We are made of star stuff
Nucleosynthesis creates elements through iron (Fe)
Supernovae create everything else 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.)? Stars have a “life process”
Star Formation Stellar Evolution Supernovae, planetary nebulae
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 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 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 Best for studying
Source of ionization (stars) Ionized gas (if unobscured, e.g. Orion)
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
Radio wavelength studies (star formation) Molecular gas (the fuel tank)
Molecular clouds Protostellar disks Molecular outflows Complex molecules
Molecules and Outflows
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 90 cm image A different view Young stars Dying stars Magnetic fields Ted LaRosa
(Kennesaw)
My Interests in this Puzzle 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 Obscured ionized gas
High density gas (young regions) Gas velocities (ionized outflows)
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
Observing with the Very Large Array
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 Optical
Extrasolar planets (Doppler shift) Protoplanetary disks (Orion) Bipolar outflows (HH objects)
Recent Discoveries Radio
Rotating protoplanetary disks Ionized and molecular outflows High density regions Outflows may support clouds
What have we learned?
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 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
Radio observations reveal... Embedded protostars Rotating molecular disks Molecular outflows Complex organic molecules
Future developments
The Millimeter Array (MMA) 36 10-meter antennas Llano de Chajnantor, Chile Elevatation-16,400 feet
VLA Upgrade (EVLA) Increased resolution New correlator (spectral line &
sensitivity) Fully equipped at 7 mm