Dr. Rachel Smullen

Top: Movie of projected density. Pink circles are single stars, blue circles are in multiples. Bottom: Distributions of core gas mass as a function of time (top panel) against the time evolution of individual cores (bottom panel). The distribution of core masses is nearly time independent, while individual cores undergo significant variability on short timescales.

Observations will never be able to study the long-term evolution of individual cores. We therefore aim to understand time-resolved core evolution using hydrodynamical simulations of a low mass star forming region. We want to better inform the big picture of the star formation process and show how individual snapshots relate to the time-varying evolution of cores.

1. Using cores identified with the dendrogram hierarchical structure method, we have developed an algorithm to follow cores through time.
2. We find that, while the global distributions of core properties match well with observations and other theoretical work, and are relatively time-independent, individual cores can have stochastic variability upwards of 50% on timescales of <50 kyr for many of the common properties measured in cores, such as mass, Mach number, and virial ⍺.
3. We find that a source of this major variability comes from how dendrograms are constructed: the dendrogram leaf contours are changing on short timescales due to small changes in the relative density structure.

Thus, we conclude that there is no time-stable density contour that defines a bound core. Because of the dynamic nature of core evolution, a single set of dendrogram parameters will not trace unique core parameters across the entire lifetime of core formation. Additionally, despite large variation in individual core properties, the overall distribution of properties evolves little in time; this contradiction call into to question the correspondence between individual core properties and the stars they produce.

Top: Movie of a scattering circumbinary system. Bottom: Fractions of outcomes for four different planet populations around binary stars and single stars. Binary stars are much more likely to suffer ejections instead of collisions.

Transiting circumbinary planets (planets that orbit two stars) as discovered by Kepler provide unique insight into binary star and planet formation. Several features of this new found population, for example the apparent pile-up of planets near the innermost stable orbit, may distinguish between formation theories. In this work, we determine how planet–planet scattering shapes planetary systems around binaries as compared to single stars. In particular, we look for signatures that arise due to differences in dynamical evolution in binary systems. We carry out a parameter study of N-body scattering simulations for four distinct planet populations around both binary and single stars. While binarity has little influence on the final system multiplicity or orbital distribution, the presence of a binary dramatically affects the means by which planets are lost from the system. Most circumbinary planets are lost due to ejections rather than planet–planet or planet–star collisions. The most massive planet in the system tends to control the evolution. Systems similar to the only observed multiplanet circumbinary system, Kepler-47, can arise from much more tightly packed, unstable systems. Only extreme initial conditions introduce differences in the final planet populations. Thus, we suggest that any intrinsic differences in the populations are imprinted by formation.