Quantifying star formation

Observations of star-forming regions only allow us to view a single snapshot in time of their evolution. By combining observations of different star-formation regions we can build up a statistical picture of how stars form in groups, how these groups dynamically evolve and eventually disperse into the field. But to fully understand how these regions formed in the first place we need to make use of numerical simulations which allow us to follow the evolution of a single star-forming region. Then we can make quantitative comparisons using a suite of methods that can be used to characterise star-forming regions (i.e. the spatial distribution of stars, or if a region is mass segregated and to what degree). By using these methods we can make inferences on not only the initial conditions of the observed star-forming regions (degree of substructure, local surface density and virial state), but also the initial conditions of planet formation. As these methods are used to infer the physics of star and planet formation they must be extensively tested on synthetic data to ensure that the methods are robust. The work herein is my investigations into the robustness of these methods on simulated data, and if these new methods can be used to reliably make inferences on the properties and physics of star-forming regions. I compare two new methods to more established and widely used methods to test their reliability. I show that INDICATE, a new clustering metric which has been used to investigate the star formation history of regions, can accurately identify areas of clustering in synthetic regions and gives results in agreement with other methods. However, INDICATE cannot be used to distinguish between star-forming regions with different morphologies, but it can be used to identify the presence of mass segregation. I investigate the evolution of phase space densities (quantified using the Mahalanobis density) of simulated star-forming regions using N -body simulations. This work was performed to better understand how the 6D phase space density evolves with time, and if its evolution depends on the initial conditions of the simulations. The method has been used to infer the likely star-formation conditions of exoplanet host stars with hot Jupiters being very dense. I find that using the 6D (position-velocity) phase space density of star-forming regions does not allow their initial conditions to be reliably discerned. I finish by investigating this possible link between the 6D phase space density of exoplanet host stars, quantified using the Mahalanobis density, and their initial formation conditions. I find that the phase space density of host stars and non-host stars does not evolve significantly differently for simulations with different initial conditions. I compare my results to previous works and find results in agreement with other works, that the Mahalanobis density is not detecting traces of the initial conditions but is instead measuring the kinematics of the host stars

Investigating the structure of star-forming regions using INDICATE

The ability to make meaningful comparisons between theoretical and observational data of star-forming regions is key to understanding the star formation process. In this paper, we test the performance of INDICATE, a new method to quantify the clustering tendencies of individual stars in a region, on synthetic star-forming regions with substructured, and smooth, centrally concentrated distributions. INDICATE quantifies the amount of stellar affiliation of each individual star, and also determines whether this affiliation is above random expectation for the star-forming region in question. We show that INDICATE cannot be used to quantify the overall structure of a region due to a degeneracy when applied to regions with different geometries. We test the ability of INDICATE to detect differences in the local stellar surface density and its ability to detect and quantify mass segregation. We then compare it to other methods such as the mass segregation ratio ΛMSR, the local stellar surface density ratio ΣLDR, and the cumulative distribution of stellar positions. INDICATE detects significant differences in the clustering tendencies of the most massive stars when they are at the centre of a smooth, centrally concentrated distribution, corresponding to areas of greater stellar surface density. When applied to a subset of the 50 most massive stars, we show INDICATE can detect signals of mass segregation. We apply INDICATE to the following nearby star-forming regions: Taurus, ONC, NGC 1333, IC 348, and ρ Ophiuchi and find a diverse range of clustering tendencies in these regions

Conversing with books: reading the eighteenth-century British periodical essay in Jeffersonian America

The periodical essay is the sole British literary genre to have emerged and declined within the chronological eighteenth century. It appeared in London during the reign of Queen Anne, and by the end of the century had virtually disappeared amidst a new culture of magazine publication. This study charts the various guises the genre assumed across the eighteenth century as essayists in Edinburgh, Philadelphia and Manhattan adapted the worldviews expressed in the earlier London essays to the particular circumstances of their cities. What the English essayists and their readers had regarded as timely, topical conversations in print about manners and culture became something more to their Scottish and American avatars. The periodical essay for them became a medium for witnessing historical change, a genre centrally concerned with what might have been. Each of the first three chapters focuses on a particular figure within the periodical essay tradition, showing how each one articulates a moral relationship to civil society that the essays' authors encourage their readers to adopt. The Censor in chapter one represents a certain manner of reading, one that means to prompt social self-reflection in the name of a broader, more comprehensive civic awareness. Chapter two takes the whimsical essayistic persona as its subject, reading whimsicality as a principled resistance to the rationalizations of time management in a developing market society, and as a direct challenge to the herd mentality periodical writers see as the real face of liberal individualism in its consumer-market guise. My third chapter shows how the Templar, a young law student who finds himself drawn increasingly to literature, comes to figure in Scottish and American essay series a perception that belletristic writing must assume a law-like moral function in recording for posterity these writers' exemplary resistance to civic decline. My final chapter then reads Washington Irving's History of New York as self-consciously drawing upon these elements of the periodical tradition to create a sort of literary conscience for a new American polity seemingly intent on reducing all of civic life to an imaginatively impoverished market for consumer goods.Ph.D.Includes bibliographical references (p. 266-286)

The evolution of phase space densities in star-forming regions

The multidimensional phase space density (both position and velocity) of star-forming regions may encode information on the initial conditions of star and planet formation. Recently, a new metric based on the Mahalanobis distance has been used to show that hot Jupiters are more likely to be found around exoplanet host stars in high six-dimensional phase space density, suggesting a more dynamic formation environment for these planets. However, later work showed that this initial result may be due to a bias in the age of hot Jupiters and the kinematics of their host stars. We test the ability of the Mahalanobis distance and density to differentiate more generally between star-forming regions with different morphologies by applying it to static regions that are either substructured or smooth and centrally concentrated. We find that the Mahalanobis distance is unable to distinguish between different morphologies, and that the initial conditions of the N-body simulations cannot be constrained using only the Mahalanobis distance or density. Furthermore, we find that the more dimensions in the phase space, the less effective the Mahalanobis density is at distinguishing between different initial conditions. We show that a combination of the mean three-dimensional (x, y, z) Mahalanobis density and the Q-parameter for a region can constrain its initial virial state. However, this is due to the discriminatory power of the Q-parameter and not from any extra information imprinted in the Mahalanobis density. We therefore recommend continued use of multiple diagnostics for determining the initial conditions of star-forming regions, rather than relying on a single multidimensional metric

The dynamical evolution of star-forming regions measured with INDICATE

Observations of star-forming regions provide snapshots in time of the star formation process, and can be compared with simulation data to constrain the initial conditions of star formation. In order to make robust inferences, different metrics must be used to quantify the spatial and kinematic distributions of stars. In this paper, we assess the suitability of the INdex to Define Inherent Clustering And TEndencies (INDICATE) method as a diagnostic to infer the initial conditions of star-forming regions that subsequently undergo dynamical evolution. We use INDICATE to measure the degree of clustering in N-body simulations of the evolution of star-forming regions with different initial conditions. We find that the clustering of individual stars, as measured by INDICATE, becomes significantly higher in simulations with higher initial stellar densities, and is higher in subvirial star-forming regions where significant amounts of dynamical mixing have occurred. We then combine INDICATE with other methods that measure the mass segregation (ΛMSR), relative stellar surface density ratio (ΣLDR), and the morphology (Q-parameter) of star-forming regions, and show that the diagnostic capability of INDICATE increases when combined with these other metrics