General Information
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First Announcement |
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Scientific Program |
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Organising Committees |
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Recent years have seen an explosive growth in the capabilities
for high angular resolution astronomical observations at all wavelength
regimes, from the x-rays to the radio. The advent of large telescopes
on the ground and in space, combined with the implementation of novel
techniques such as adaptive optics and interferometry, allow us to explore
the universe in unprecedented detail. With these dramatic improvements
in resolution come the prospect of significant advances in understanding
a wide range of cosmic phenomena. In particular, high angular resolution
observations have begun to play a vital role in studies of the star formation
process, providing new insights and testing physical models. That role
is likely to become even more dominant over the next decade as instruments
such as the Australia Telescope Compact Array, Keck and VLT Interferometers,
Sub-Millimeter Array and the Atacama Large Millimetre Array commence operations.
The large and steadily increasing number of papers on star formation that
are based on high resolution studies at X-ray, optical, infrared, millimetre,
and radio wavelengths testifies to the vigour and timely appeal of this
topic.
IAU Symposium 221 will review what we have already learned about the
star formation process through high angular resolution observations and
discuss the prospects for progress with the wide variety of new instruments
that will become available over the next decade. The Symposium will address
molecular clouds and their protostellar cores; jets, outflows and disks;
problems of low-mass and high-mass star formation; extragalactic star
formation; and the influence and detection of planets during star formation.
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Scientific Program
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Molecular clouds to protostellar
cores
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Star formation takes place within dense cores inside molecular
clouds. It is both a cold and an obscured process. Sub-mm and mm-wave
observations are therefore needed to probe the first stages of the collapse
process. Large single-dish telescopes can identify where cores are, but
interferometric techniques are required to study their structure. It is
also apparent that the collapse is associated with a rich chemistry, with
segregation of different chemical species occurring. The chemical signature
also provides an indicator of the evolutionary state that different parts
of a molecular cloud have reached. However, whether 'hot molecular cores'
are simply a by-product of star formation, or an integral part of the
process, has yet to be determined. High spatial resolution is necessary
to separate the different environmental regimes within the clouds from
one another, and to determine their relation with one another. Mm and
sub-mm interferometers provide the tools to do this, in particular the
Sub-Millimeter Array (SMA). |
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Low mass star formation
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Low mass star formation is common throughout the galaxy,
but can best be studied within a few hundred parsecs due to its relative
feebleness compared to massive star formation. High-resolution observations
at a wide range of wavelengths are critical for probing the physical phenomena
associated with the birth of low-mass stars. The early embedded phase
of newborn stars is poorly explored. Recent observations have found inverse
P-Cygni profiles in mm molecular lines, strong evidence for gravitational
infall. Determining the density structure in the inner, densest regions
of protostellar cores is the best way to discriminate between theoretical
models. There appear to be conflicting statistics on the frequency of
binaries in different star-forming regions, and issue best tackled with
high resolution. Another nagging issue is the shape of the initial mass
function (IMF) in different environments, especially at the very low masses.
Recent results suggest that the IMF may vary
"locally'' even though it may be universal in a global sense. All
of these topics can only be addressed with
high angular resolution observations, particularly at mm/sub-mm wavelengths,
and in the near-infrared. |
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Massive Star Formation |
Massive star formation takes place in clusters, in conditions
which are both crowded and confused. Despite its luminosity, which enables
a complete census of massive star formation to be undertaken in the galaxy,
it is still a poorly understood process. This is because of the many interacting
phenomena associated with it, for which it is hard to disentangle cause
and effect, and the short timescale on which they occur. Indeed, the radiation
pressure generated by a massive protostar, once it has reached 10 Msun,
would seem sufficient to be able to halt any further accretion, so it
remains a mystery how higher mass stars are formed at all. It has even
been suggested that massive stars form via coalescence of lower mass (<
10 Msun) stars, inside exceedingly dense cluster environments. If so,
they do so at stellar densities that have not been probed yet. Several
developments have occurred recently which provide new tools for the study
of massive star formation. Mid-IR imaging cameras are now available on
the 8-m class optical/IR telescopes, equipped with a suite of filters
for working between 8-30µm. Their diffraction limited observations
provide an order of magnitude gain in speed over capabilities of 4-m class
telescopes. The interaction of the young stars with their molecular clouds
is also probed by a variety of spectral lines in the thermal-IR. Associated
phenomena include masers, particularly water and methanol masers, which
provide clear signposts to the presence of massive star formation across
the galaxy. It is not clear what their direct association with star formation
is, however. Are the masers in disks around embedded sources, sites where
shocks are interacting with molecular gas, or simply fortuitous sight
lines through hot molecular cores? Interferometry allows not only the
relative location of masers and embedded sources to be ascertained, but
also the structure within groups of maser spots. |
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Extragalactic Star
Formation |
Star formation studies in external galaxies allow us to
study modes of star formation and physical conditions that can be very
different from those found in our own Galaxy. For example, studying the
formation of massive young clusters in mergers and merger remnants may
allow us to understand how the similar-mass globular clusters formed in
the early universe. The LMC, SMC, and other nearby dwarf galaxies allow
us to study the effect of metallicity on the star formation process, which
will be important for accurate models of star formation in primeval galaxies.
On larger scales, understanding what triggers a starburst and how star
formation is regulated in galactic disks remain challenging problems for
which high-resolution studies are yielding new insights. |
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Jets, Outflows and Disks |
Perhaps more than any other area in star formation, the
study of the phenomena of jets, outflows and disks stands to benefit from
high spatial resolution studies. Diffraction-limited imaging from space
in the optical and X-ray, and near-diffraction limited imaging in the
near-IR with AO systems, provides the capability to resolve structure
in these phenomena. Proper motions in outflows can be discerned and entrainment
with the ambient medium examined. Disk sizes can be determined, and internal
structures (e.g. central holes, temperature gradients) ascertained. With
the commissioning of mid-IR interferometers, such as on the Keck and VLTI,
the internal structure in disks may be examined, in particular the transition
from proto-planetary disk to debris disk. For instance, it should be possible
to measure zodiacal light contributions in a variety of systems. |
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Planets |
Until now, all extra-solar planet detections have been
made through radial velocity measurements and transit photometry. However,
the imaging detection of a young Jupiter analogue around a nearby star
is within the reach of current adaptive optics systems on 8- to 10-metre
telescopes. Giant planets are hottest and brightest when young, making
them significantly easier to detect through near-infrared imaging than
their older counterparts. AO searches at Subaru, Keck, Gemini, and VLT
can not only detect candidate young planets, but also provide confirmation
of their nature through follow-up proper motion and spectroscopic observations.
With the advent of the Keck and VLT Interferometers, it may also be possible
to detect older giant planets (or at least brown dwarfs) around nearby
main sequence stars, particularly with the use of nulling in the thermal
infrared. |
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Scientific Committee |
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Local Committee |
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Michael Burton (Australia, Chair)
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Tyler Bourke (USA, Co-chair)
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Ray Jayawardhana (USA, Co-Chair)
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Catherine Cesarsky (IAU)
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Thomas Henning (Germany)
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Katsuji Koyama (Japan)
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Anne-Marie Lagrange (France)
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Diego Mardones (Chile)
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Young Chol Minh (Korea)
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Antonella Natta (Italy)
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Tom Ray (Ireland)
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Luis Rodriguez (Mexico)
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Anneila Sargent (USA)
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Christine Wilson (Canada)
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- Michael Burton
- Maria Hunt
- Vincent Minier
- Kate Brooks
- Peter Barnes
- Melinda Taylor
- Jon Everett
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