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One of the main challenges to the formation of stars is the ?angular momentum problem?: the gas contained in a typical star-forming core must reduce its specific angular momentum by 5 to 10 orders of magnitude to form a typical star such as our Sun, or else centrifugal forces will soon balance gravity and prevent inflow, accretion and the growth of the protostellar embryo (Bodenheimer, 1995).
Early analytical analysis (Terebey et al. 1984, Shu, Adams, & Lizano, 1987) proposed that the formation of large (r > 100 AU) centrifugally supported disks in the protostellar cores would allow to transfer angular momentum outward and therefore solve the angular momentum problem.
Indeed, protoplanetary disks with radii 50-200 AU are routinely observed around young T-Tauri stars, however we still don?t know how the progenitors of these disks are formed during the earliest phases of protostellar formation. In fact, not much is known on the structure of circumstellar envelopes surrounding the youngest (Class 0) protostars at the small scales, due to a lack of observations of Class 0 objects at resolutions probing
the <100 AU scales (1'' resolution or better) in the (sub-)millimeter domain where they emit most of their energy.
Characterizing the chemical and physical structure of the inner regions of the youngest protostellar envelopes is crucial to solve the angular momentum problem, and ultimately constrain the formation and evolution models of solar-type stars (origin of the stellar initial mass function, formation of the multiple stellar systems, disks and planets).
In order to tackle this issue, we obtained a large observing program with the Plateau de Bure interferometer (PdBI) and the IRAM 30m telescope. This large program, named CALYPSO (Continuum and Line in Young Protostellar Objects, PI Philippe André), consists in observing the line and continuum emission from an unprecedentedly large sample of 17 very young (Class 0) protostars at high spatial resolutions (0.5'' i.e. 50-100 AU).
The main objective of the proposed thesis project is to characterize the physical and chemical structure of protostellar envelopes on the small scales where disks are observed in more evolved YSOs, therefore testing if the formation of disks is indeed an outcome of, and solution to, the angular momentum problem for star formation.
The PhD student will analyze and interpret high-angular resolution millimeter observations of Class 0 protostars obtained with the PdBI as part of the CALYPSO program, in close collaboration with the CALYPSO working group interested in disk formation questions (Philippe André, Anaëlle Maury, Sébastien Maret, Leonardo Testi and Patrick Hennebelle). He/she will also propose follow-up observations with the NOEMA and ALMA observatories. Moreover, the student will contribute in comparing these observations with the predictions of numerical models for protostellar formation and evolution, in close collaboration with the Chemodyn(Sébastien Maret, Sibylle Anderl, Benoit Commerçon) team.