Toward Understanding the Formation of Proto-planetary Disks and Multiple Star Systems

Séminaire IPAG de John Tobin (Leiden), jeudi 9 avril 2015 à 11h00, IPAG seminar room

Disks and multiple star systems are thought to form early in the star formation process. Conservation of angular momentum enables the formation of protostellar disks and protostellar companions can also form if the disk is gravitationlly unstable. However, theory and simulations have suggested disk formation and multiple star formation may be difficult due to removal of angular momentum by magnetic fields. Observations are now sensitive enough to begin testing these predictions and I will present my discovery of the first rotationally-supported (Keplerian) disk around a protostar in the earliest phase of evolution. This discovery has led the way for further ALMA studies of disks in similarly young systems.

Despite this recent progress, the number of known Keplerian disks around the youngest protostars remains small and the frequency of companion protostars on scales < 150 AU is unconstrained. To greatly expand our knowledge on the frequency of disks and multiplicity, I am leading a 264 hour VLA large program to observe all protostars in a single star forming region, the Perseus molecular cloud (d 230 pc, N 80), with a spatial resolution of 15 AU With these data, we are identifing new protostellar disk candidates and closer multiple systems than have ever been previously identified toward such young protostars. We have found evidence for a bimodal distribution of protostar separations, with a peak at 80 AU and another at 3000 AU. This result is suggestive of multiple formation mechanisms on different scales. Finally, we also see indications of evolution in the separation distribution for younger and more-evolved protostars. The characterization of the newly discovered multiples and disk candidates is just beginning ; approved ALMA molecular line kinematic observations will be key to determining the origin and fate of these multiple systems. Moreover, these results open the door to expanded multiplicity surveys to determine if the trends we find are applicable to other star forming regions.