Informal Colloquium
Caroline Gieser	SCHEDULED

Max-Planck-Institut für Astronomie, Heidelberg

During high-mass star formation, fragmentation takes place on various spatial scales from giant molecular clouds down to disk scales. At the earliest evolutionary stages, high-mass protostars are still deeply embedded within their parental molecular cloud and can be studied best at high spatial resolution with interferometers at mm wavelengths. The IRAM/NOEMA large program CORE allows us to analyze the physical and chemical properties of a sample of luminous high-mass star-forming regions. The 1 mm dust continuum of the sample shows a large diversity of fragmentation properties. Using the spectral line emission, we are able to determine the physical structure (temperature and density) and molecular content of individual fragmented cores. Even though all regions are classified to harbor high-mass protostellar objects, the molecular content shows a high degree of complexity. By combining the observed core properties, we are able to estimate chemical timescales with the physical-chemical model MUSCLE. We find well-constrained density and temperature profiles in agreement with theoretical predictions. The molecular complexity in the core spectra can be explained by an age spread that is then confirmed by our physical-chemical modeling. The hot molecular cores show the greatest number of emission lines, but we also find evolved cores in which most molecules are destroyed and, thus, the spectra appear line-poor once again. Currently, we are expanding our sample with ALMA 3 mm observations of 11 additional high-mass star-forming regions at different evolutionary stages - from infrared dark clouds to ultra-compact HII regions - in order to further investigate the evolution of the physical and chemical properties on core scales.

	Main Colloquium
Dr. John Tobin	SCHEDULED

National Radio Astronomy Observatory, Charlottesville, USA

The formation of disks and multiple star systems are integral parts of the star and planet formation process. Most stellar mass must be accreted through a disk, disks are the future sites of planet formation, and disks will also give rise to companion stars. Using ALMA and the VLA, we are conducting large continuum surveys of protostars (with molecular lines toward a subset of the full sample) in the nearby Perseus and Orion star-forming regions (with 20-30 au resolution) to characterize the disk radii, disk masses, and frequency of multiplicity throughout the protostellar phase. The molecular line data enable us to measure the masses of the protostars and we are beginning to identify and characterize the formation environments of both low and intermediate mass protostars. We find clear changes in multiplicity properties with evolution that link back to their formation mechanisms, establishing a foundation from which multiplicity evolution must begin.