Filtering by
- Member of: Theses and Dissertations
Debris disks are a collection of dust grains and planetesimals around a star and are thought to contain the remnants of planet formation. Directly imaging debris disks and studying their morphologies is valuable for studying the planet formation process. In some stellar systems that have a directly imaged debris disk, there are also directly imaged planets. Debris disk structures like gaps and asymmetries can show the gravitational e↵ects of planets that are below the brightness threshold for being detected via direct imaging. We investigate a sample of debris disks in Scorpius-Centaurus (Sco-Cen) that were imaged with the Gemini Planet Imager (GPI), which is an adaptive optics system with a coronagraph to block starlight. We look at two GPI data sets, the GPIES campaign Sco-Cen targets, and a follow-up observing program for Sco-Cen targets. We resolve 5 debris disks in the follow-up program and 13 from the GPIES campaign. By calculating contrast curves, we determine the planet detection limit in each of the GPI images. We find that we could have detected 5 Jupiter mass planets at angular separations greater than about 0.6 arcseconds in our GPIES campaign images. In three of our images we could have detected 2 Jupiter mass planets in wide orbits, but 2 Jupiter masses below the detection limit in our other images. We identify one point source around HD 108904 as a sub-stellar companion candidate. To further check for evidence of planets that are below the detection limit, we measure the surface brightness profile of the disks to check for asymmetries in brightness. We find that one of the edge-on disks has an asymmetric surface brightness profile, HD 106906, and three other edge-on disks have symmetric surface brightness profiles. We also find that two disks, HD 106906 and HD 111520, are asymmetric in radial extent, which is possibly evidence for gravitational interactions with planets.
Part II – I examine time-resolved neutron data from the Dynamic Albedo of Neutrons (DAN) instrument on the Mars Science Laboratory (MSL) Curiosity rover. I personally and independently developed a data analysis routine (described in the supplementary material in Chapter 2) that utilizes spectra from Monte Carlo N-Particle Transport models of the experiment and the Markov-chain Monte Carlo method to estimate bulk soil/rock properties. The method also identifies cross-correlation and degeneracies. I use data from two measurement campaigns that I targeted during remote operations at ASU. I find that alteration zones of a sandstone unit in Gale crater are markedly elevated in H content from the parent rock, consistent with the presence of amorphous silica. I posit that these deposits were formed by the most recent aqueous alteration events in the crater, since subsequent events would have produced matured forms of silica that were not observed. I also find that active dunes in Gale crater contain minimal water and I developed a Monte Carlo phase analysis routine to understand the amorphous materials in the dunes.
The first extrasolar planet discovered orbited the millisecond pulsar PSR B1257+12. These so-called "pulsar planets" have proved to be more uncommon than their early discovery might have suggested. The proximity of many known pulsar planets to their host neutron stars indicates that they formed post-supernova, possibly from material produced in the supernova. Any pre-existing planets that close would have been obliterated in the supernova. Material from the supernova falls back to an accretion disk around the neutron star analogous to a protoplanetary disk around a protostar. The composition of the supernova thus determines the composition of the planet-forming material. The pulsar planet then forms from collisions between particles within the disk. This research examines the composition of supernova remnants to explore this formation process. Chemical abundances of supernova ejecta were obtained from 3D supernova simulations. The velocities of particles containing silicate-mineral forming elements were filtered to determine what might stay in the system and thus be available for the formation of a fallback disk. The abundances of the remaining particles were compared to characterize the potential composition of such a fallback disk. Overall, the composition was roughly silicate-like, but the rates of mixing versus dust formation could lead to the production of highly exotic minerals.
First, I numerically investigated the flow structures and dynamics of the primary atmospheres accreted on Earth-sized planets with eccentric orbits. Such planets can generate atmosphere-stripping bow shocks, as their relative velocities to the gas are generally supersonic. The atmospheres are three to four orders of magnitude less massive than those of planets with circular orbits. Hydrodynamic simulations also revealed large-scale recycling gas flow in the post-shock regions. This study provides important insights into the impacts of migration and scattering on primary atmospheres.
Second, I looked into how the presence of the primary atmosphere affects the trajectories of chondrule precursors passing through a planetary bow shock. To determine what magnetic fields chondrules were exposed to as they cooled below their Curie points, I computed the gas properties and magnetic diffusion rates in the bow shock region of a planet with and without the primary atmosphere. I concluded that, if melted in planetary bow shocks, most chondrules were cooled in the far downstream and they probably recorded the background nebular field.
Last, I studied the characterization of cloudy primary atmospheres on exoplanets using a Bayesian retrieval approach. I focused on obtaining bulk cloud properties and the impact of clouds on constraining various atmospheric properties through transmission spectroscopy using the James Webb Space Telescope (JWST). Most key atmospheric and cloud inferences can be well constrained in the wavelength range (0.6 – 11 µ m) but there are different optimal wavelengths for constraining atmosphere or cloud parameters. Other results including degeneracies among cloud parameters can also serve as a guideline for future observers.