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2010 Spring Symposium

The Where, When, Why, and How of Star Formation in the Local Group

Presented by: Guido de Marchi  (European Space Agency)
Category: Science Symposium   Duration: 20 minutes   Broadcast date: May 03, 2010
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We have undertaken a systematic study of pre-main-sequence (PMS) stars spanning a wide range of masses (0.5 - 4 Msolar), metallicities (0.1 - 1 Zsolar) and ages (0.5 - 30 Myr). We have already used new WFC3 and archival ACS data to identify and characterise a large sample of PMS objects in three star forming regions in the local group, namely NGC 3603 in the Milky Way, 30 Doradus in the Large Magellanic Cloud and NGC 346 in the Small Magellanic Cloud. Thanks to a novel method that we have developed to combine broad-band (V,I) photometry with narrow-band Halpha imaging, we have determined the physical parameters (temperature, luminosity, age, mass and mass accretion rate) of more than 2000 bona-fide PMS stars still undergoing active mass accretion. This is presently the largest and most homogeneous sample of PMS objects with known physical properties. We will present the most important results of this research, including: (1) All regions exhibit multiple recent episodes of star formation with at least two populations of younger and older PMS stars separated by about 10 Myr from each other, suggesting a multi-generation pattern; (2) There is no correlation between the projected spatial distribution of young and old PMS stars and the younger population is systematically more concentrated, contrary to what one could expect in a triggered star formation scenario; (3) There is no correspondence between the positions of young PMS stars and those of massive OB stars of similar age, indicating that the conditions necessary for high- and low-mass star formations are different; (4) The mass distribution of stars with similar ages reveals large variations throughout the regions, showing that the concept of initial mass function is not meaningful for individual star forming units (~5pc in size); (5) The mass accretion rate appears to scale with the first power of the stellar mass, with the square root of the age, and approximately with the inverse of metallicity. These results are bound to have important consequences for, and constraints on our understanding of the star formation process.

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Guido de Marchi's presentation PDF document (.pdf)