The statistics of stellar multiple systems formed from small subclusters

Ambrose, Hannah 2025. The statistics of stellar multiple systems formed from small subclusters. PhD Thesis, Cardiff University. Item availability restricted.

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Abstract

The early life of small stellar subclusters – particularly as they evolve from the protostellar phase to stable main sequence systems – is poorly understood. In this thesis, I investigate the dynamical evolution of subclusters over this stellar adolescent phase. I model isolated subclusters with different numbers of stars, N , and previously unexplored initial conditions (such as ordered rotation) and evolve them using an n-body algorithm. I derive an equation to generate the possible end states that these subclusters can produce. I also present a prescription for mixing the statistics generated by different values of N , which I use to investigate cores that produce a range in number of stars. I analyze the multiplicity statistics and architectures of the final systems, and compare them with the solar-mass primary statistics from Tokovinin (2021). Through this comparison, I derive predictions about the initial conditions of subclusters as they leave the protostellar phase. To produce the best fit to the observed statistics, I find that prestellar cores must typically spawn between 4.3 and 5.2 stars. Subclusters that begin with roughly half their kinetic energy invested in rotation produce the best fits to the Tokovinin (2021) sample. These properties are also compatible with the observed Orbital Statistics, i.e. the distributions of semi-major axis, mass ratio, eccentricity and mutual inclination and eccentricity. The observed distribution of mutual inclinations in particular favours an average N of 4.8. The Best-Fit properties produce a similarly shaped mutual orbital inclination distribution as observations, with a phase offset. The initial number of stars in the subcluster, N , has the greatest effect on the systems it produces, influencing periods and separations, dynamical biasing, plurality, mutual orbital inclinations, and ejection timescales. The fraction of kinetic energy in ordered rotation and the degree of mass segregation also have an effect on some of these statistics. For the Best-Fit Case, I find that 21(\pm 1)% of subclusters spawn two or more multiple systems.

Item Type:	Thesis (PhD)
Date Type:	Completion
Status:	Unpublished
Schools:	Schools > Physics and Astronomy
Subjects:	Q Science > QB Astronomy Q Science > QC Physics
Uncontrolled Keywords:	stellar multiplicity, binaries, star bformation, celestial mechanics
Funders:	STFC
Date of First Compliant Deposit:	6 January 2026
Last Modified:	06 Jan 2026 15:09
URI:	https://orca.cardiff.ac.uk/id/eprint/183593

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