Seeing Stars with Radio Eyes Christopher G. De Pree RARE CATS Green Bank, WV June 2002

Overview n Why study star formation? n Some unanswered questions in star formation n Successes and limitations of optical wavelength studies n Advantages of radio wavelength studies n Recent discoveries in star formation n Conclusions

Why study Star Formation? n We are made of star stuff u Nucleosynthesis creates elements through iron (Fe) u Supernovae create everything else n The death and birth of stars may be linked (triggered star formation) n Complex molecules can form on dust grains near young stars n Young stars “stir up” clouds of gas

Why study Star Formation (cont.)? n Stars have a “life process” u Star Formation u Stellar Evolution u Supernovae, planetary nebulae n Where there are stars, there are planets n Effect on galactic evolution u The Antennae (Arp 224) u Andromeda HST with CO (BIMA)

Giant Molecular Clouds in Andromeda

The Process of Star Formation n Collapsing molecular cloud core n Inside-out collapse produces a protostar plus accretion disk n Bipolar molecular outflow carries away angular momentum n What do we look for to see the earliest stages? u Dense cloud cores u Infalling molecular material u Molecular disks/outflows

Jet Example: Core of NGC 2071

Open questions in star formation n Do all stars form planets? n Are accretion disks common to all star masses? n Do all young stars have outflows? For how long? n Do massive stars (>5 solar mass) form differently than low mass stars? n Do massive star outflows “stir up” molecular clouds?

Optical wavelength studies n Best for studying u Source of ionization (stars) u Ionized gas (if unobscured, e.g. Orion) n Potential problems u Star forming regions are often highly obscured (e.g. NGC 253) u The early stages of star formation are not optically visible (radio, infrared) u Molecular material (fuel tank) best detected at radio frequencies u Deeply embedded ionized material best detected at radio frequencies

Radio wavelength studies (star formation) n Molecular gas (the fuel tank) u Molecular clouds u Protostellar disks u Molecular outflows u Complex molecules

Molecules and Outflows n Molecules in Orion n Distribution of molecules n Abundance of molecules n Source motions (rotations and outflows) n Presence of complex molecules n Potential for pre-life chemistry

Viewing the Milky Way Galaxy n 90 cm image n A different view n Young stars n Dying stars n Magnetic fields n Ted LaRosa (Kennesaw)

My Interests in this Puzzle n HII Regions (regions of ionized gas around massive stars) n High resolution imaging of the ionized gas n Kinematics (motions) of the ionized gas n Understanding the earliest stages of massive star formation

Radio wavelength studies of HII Regions n Obscured ionized gas u High density gas (young regions) u Gas velocities (ionized outflows) n Ionized shells at the centers of outflows (e.g. G5.89 Observed with the VLA) n Disadvantage: resolution u Very Large Array (VLA) u Berkeley Illinois Maryland Association u Owens Valley Radio Observatory u But: VLA at 7 mm—same resolution as the Hubble Space Telescope

Observing with the Very Large Array n

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 n Optical u Extrasolar planets (Doppler shift) u Protoplanetary disks (Orion) u Bipolar outflows (HH objects)

Recent Discoveries n Radio u Rotating protoplanetary disks u Ionized and molecular outflows u High density regions u Outflows may support clouds

What have we learned? n Some HII regions are much smaller and far brighter than previously thought n “Typical” HII regions were thought to be ~1 pc in diameter n “Typical ultracompact” HII regions that we study are ~0.01 pc in diameter n These new sources are younger and brighter—give us insight into an earlier phase of star formation n Spectral line detections—we see rotation and outflow in many sources

Conclusions n Star formation studies tell us about... u Chemical evolution of the universe u Structure and evolution of galaxies u Enrichment of the space between the stars (the ISM) u Abundance of elements u Prevalence of planets n Radio observations reveal... u Embedded protostars u Rotating molecular disks u Molecular outflows u Complex organic molecules

Future developments n The Millimeter Array (MMA) u meter antennas u Llano de Chajnantor, Chile u Elevatation-16,400 feet n VLA Upgrade (EVLA) u Increased resolution u New correlator (spectral line & sensitivity) u Fully equipped at 7 mm