IAU Symposium 221


Star Formation at High Angular Resolution

IAU GA XXV | General Info | Conference Program | Poster Papers | Submitting Contributions

General Information


First Announcement


Scientific Program


Organising Committees


Scientific Rationale

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.


Scientific Program


Molecular clouds to protostellar cores


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).


Low mass star formation


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.


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.


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.


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.



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.


Organising Committees


Scientific Committee


Local Committee

  • Michael Burton (Australia, Chair)

  • Tyler Bourke (USA, Co-chair)

  • Ray Jayawardhana (USA, Co-Chair)

  • Catherine Cesarsky (IAU)

  • Thomas Henning (Germany)

  • Katsuji Koyama (Japan)

  • Anne-Marie Lagrange (France)

  • Diego Mardones (Chile)

  • Young Chol Minh (Korea)

  • Antonella Natta (Italy)

  • Tom Ray (Ireland)

  • Luis Rodriguez (Mexico)

  • Anneila Sargent (USA)

  • Christine Wilson (Canada)

  • Michael Burton
  • Maria Hunt
  • Vincent Minier
  • Kate Brooks
  • Peter Barnes
  • Melinda Taylor
  • Jon Everett


UNSW | School of Physics | Department of Astrophysics and Optics | Astronomy in Antarctica

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Contact Details

Last updated: 23/09/2004


E-mail: iau221@phys.unsw.edu.au

Created and maintained by Steven Longmore