Abstract: In the earliest stages of low-mass star formation, the central protostar is deeply embedded and accreting matter through a circumstellar disk. Understanding the physical and chemical properties of these young stellar objects is important, since they define the future evolution of the system including its potential to form planets. In this talk I will discuss the results of an extensive study of the physical and chemical structure of a sample of deeply embedded protostars. Based on single-dish continuum and line observations, the temperature, density and abundance profiles of the protostellar envelopes are determined through detailed radiative transfer modeling. Subsequent high-resolution interferometer observations constrain the properties of the protostars down to a few AU scales. These results provide interesting new insights into the deeply embedded stages of low-mass protostellar evolution, e.g., in relation to the physical and chemical structure and evolution of the envelope, to the importance of outflows and the formation of circumstellar disks. In particular, I will emphasize how and where the SMA will be important in the studies of these early stages of star formation and present a few results from our ongoing large survey.
Wednesday, February 23rd
Speaker: J-M. Girart, ICE-CSIC, Barcelona
Title: Evidence for Transient Clumps and Gas
Evolution in Molecular Clouds
Abstract: In this talk I will talk about FCRAO and BIMA observations dones towards a starless region of the L673 molecular cloud. The FCRAO maps show a filamentary structure with clear morphological differences for each molecule. We find that HCO+ has an extremely high optical depth, and that the H13CO+ emission is well correlated with submm sources. The BIMA and FCRAO combined maps show an overall aspect of a filamentary structure connecting several intense clumps with diameters in the 0.03-0.09 pc range. The derived clump masses are below the virial mass, and the clumps masses become closer to the virial mass when they get bigger and more massive. This supports the idea that these clumps must be transient, and only the more massive ones have a chance to last long enough to form stars. The clumps we detect are probably in an earlier evolutionary stage than the ``starless cores'' reported recently in the literature. Only the most massive one has properties similar to a ``starless core''.
Monday, February 14th
Speaker: D. Li, Astronomer, CfA
Title: How Fast Can it Be: Constraining the Formation
Time Scale of Clouds and Stars.
Abstract: The time scale of star formation is a fundamental aspect of our understanding of ISM and Galactic evolution. In the "standard" theoretical frame work involving ambipolar diffusion and inside out collapse, the time scale is regulated by magnetic field and it is around 10 Myr. Recent developments in measuring stellar cluster age and large scale mapping of the ISM, however, prompt different proposals of star formation in one dynamical time scale (Elmegreen 2001) and fast structure and star formation in 1-2 million years (Hartmann et al. 2004).
Our HI narrow self-absorption study of low mass cores provide a strong observational limit to the evolutionary time of such cores(Li & Goldsmith 2003; Goldsmith & Li 2004). The main result is that it take more than 5 to 10 Myr to form dense molecular structures from atomic gas. Our observation of the "starless" region of the Orion molecular clouds reveal evidence of fragmentation along the filament and virial equilibrium 0.1 pc scale, which excludes supercritical collapse on that scale (Li et al. 2003). Further large surveys of low (Taurus), medium (Ophiuchus), and high (Orion) mass star forming regions will provide more definitive constrains regarding the time scales of their formation.
Tuesday, November 30th, 2004
Speaker: G. Petitpas, SMA Postdoc, CfA
Title: The Dark Matter Content of Barred Spiral Galaxies
Abstract: Observations of the gas kinematics in barred spiral galaxies can be used to determine the relative masses of the stellar disk and the dark matter halo in the centers of galaxies (e.g. Weiner et al. 2001). The gas flow in bars depends on the non-axisymmetry in the stellar mass distribution, so a comparison of the simulated and observed velocity fields in a bar can be used to determine the contribution of the stellar mass to the total dynamical mass in the disk of a galaxy. This reveals to what extent the "Maximum Disk" is achieved in barred spiral galaxies. Unlike previous studies of this sort, we use a larger sample of galaxies taken from the BIMA SONG survey complemented with new 2" BIMA CO J=1-0 data. We present details of the techniques used in the project and some early results of our investigations.
Tuesday, November 16th, 2004
Speaker: Sun Kwok, Director, ASIAA
Title: The Odin Submillimeter Satellite
Abstract:
The Odin Submillimeter Satellite is a joint mission
between Sweden, Canada, France and Finland. It is the second submillieter
telescope in space (after SWAS), and the first with tunable receivers.
Odin carries a 1.1m telescope and 4 submillieter receivers centered on
495, 548, 555, and 571 GHz. There is also a millimeter receiver at 119 GHz
for the ground-state transition of oxygen molecule. Odin was successfully
launched in February 2001, and has been operating for over 3 years. In
addition to the search and observations of water and oxygen molecules,
Odin has the unique capability to perform the first spectral scan in
the submillieter spectral window. We will present the highlights of
the science results from Odin, with specific emphasis on the work done
at the University of Calgary in Canada.
Meeting History until August 2004
For questions and comments:
rrao@cfa.harvard.edu
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