The time evolution of star forming cores

With Dr. Kaitlin Kratter, Dr. Stella Offner, Dr. Aaron Lee, & Dr. Hope Chen

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.

This paper is under review at MNRAS and can be found on arXiv: 2004.01263

The architecture of circumbinary systems

With Dr. Kaitlin Kratter & Dr. Andrew Shannon

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.

Look for our paper in MNRAS, on arXiv and ADS.

The fate of debris around the Pluto-Charon system

With Dr. Kaitlin Kratter

Top: Movie of the dynamics of test particles in the Pluto-Charon circumbinary system. Bottom: The stability limits of circumbinary debris around the migrating Pluto-Charon binary. Because the stability limits cross the orbits of Pluto-Charon's current circumbinary moons, the moons cannot have been formed in situ.

The Pluto–Charon system has come into sharper focus following the flyby of New Horizons. We use N-body simulations to probe the unique dynamical history of this binary dwarf planet system. We follow the evolution of the debris disc that might have formed during the Charon-forming giant impact. First, we note that in situ formation of the four circumbinary moons is extremely difficult if Charon undergoes eccentric tidal evolution. We track collisions of disc debris with Charon, estimating that hundreds to hundreds of thousands of visible craters might arise from 0.3–5 km radius bodies. New Horizons data suggesting a dearth of these small craters may place constraints on the disc properties. While tidal heating will erase some of the cratering history, both tidal and radiogenic heating may also make it possible to differentiate disc debris craters from Kuiper belt object craters. We also track the debris ejected from the Pluto–Charon system into the Solar system; while most of this debris is ultimately lost from the Solar system, a few tens of 10–30 km radius bodies could survive as a Pluto–Charon collisional family. Most are plutinos in the 3:2 resonance with Neptune, while a small number populate nearby resonances. We show that migration of the giant planets early in the Solar system's history would not destroy this collisional family. Finally, we suggest that identification of such a family would likely need to be based on composition as they show minimal clustering in relevant orbital parameters.

Look for our paper in MNRAS, on ADS, or on an arXiv near you!

Machine learning identification of Kuiper belt populations

With Dr. Kat Volk

Top: The classification of KBOs. Color indicates class (purple are resonant, blue are classical). We have a >97% accuracy on classification in the four populations. Squares show objects that were classified incorrectly. Bottom: the probability of class membership. About 80% of our objects have a more than three-sigma probability of belonging to the correct class. Those that are misclassified are typically misclassified because of late time orbital changes that the classifier does not know about.

With the immenent era of big data (such as the Vera Rubin Observatory—formerly LSST—which will produce about 20TB of observations a night and is predicted to find tens of thousands of Kuiper Belt objects), we must think of faster, more automated ways to sort through observations of objects such as Kuiper Belt objects (KBOs). Thus, we use a machine learning classifier to classify KBOs based on the dominant features in short numerical simulations of their orbits in order to sort the KBOs into the four dominant dynamical populations: classical (primordial from the formation of the Solar System), resonant (under the dynamical control of Neptune), detatched (outside the current boundary of the Kuiper Belt), and scattering (having an actively evolving orbit that will likely lead to ejection from the Solar System). The use of machine learning will allow faster classification of common types of objects, thereby requiring astronomer intervention only on the most interesting objects.

Coming soon!

Other Projects

Heartbeat stars: with Dr. Chip Kobulnicky
We used the Wyoming Infrared Observatory to do a radial velocity survey of six eccentric binary systems. Our goal was to test the validity of a model that extracts information about the binary orbit from the light curve.
Look for our paper in ApJ, on arXiv, or on ADS.
Finding satellite galaxies of ESO 243-49: with Dr. Janine Pforr
We photometrically searched for satellite galaxies around ESO 243-49 (a galaxy that is thought to host the first known intermediate-mass black hole) using Hubble images.
Look at our 2014 AAS presentation on ADS.
Imaging the spatial density within starburst galaxies: with Dr. Jeff Mangum
This was a pilot survey using the VLA to study formaldehyde in nearby starburst galaxies. Formaldehyde, you say? Turns out that it is a very sensitive tracer of molecular hydrogen.
Look at our 2013 AAS presentation on ADS.
Massive binaries in the Cygnus OB2 Association: with Dr. Chip Kobulnicky
My first research project. Ah, those were the days. We used the Wyoming Infrared Observatory to continue a radial velocity survey of massive stars to search for binary companions.
Look at our paper on ADS or in ApJ, or find our 2012 AAS presentation on ADS.