Author ORCID Identifier

https://orcid.org/0000-0002-1864-6120

Date of Award

8-8-2023

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Physics and Astronomy

First Advisor

Todd Henry

Second Advisor

Jessie Christiansen

Third Advisor

Sebastien Lepine

Fourth Advisor

Russel White

Abstract

The M dwarfs are the most numerous stars in our neighborhood, and considering that 27% of them are in systems of two or more stars, this dissertation surveys how these multiples behave dynamically to establish the orbital parameter distributions for companions with orbital periods up to 30 years. This work encompasses the regimes of several observing techniques: (1) astrometry from the 23-year RECONS program at CTIO, (2) speckle interferometry from SOAR HRCam+SAM, and (3) imaging and spectroscopic orbits from the literature. Through this effort we have increased the number of nearby M dwarf orbits by roughly a third, and updated or improved several dozen as well. This combined data set of nearly 200 orbits reveals three new fundamental results. The first is that the tidal circularization period is within 4--7 days for M dwarfs, shorter than for solar-type binaries. The second is that the eccentricity distribution at periods >5 years depends on the primary star mass and potentially the mass ratio, as nearly-circular orbits occur only for systems in which at least one component is Sun. The third result is that mass ratios of M dwarf multiples are strongly weighted toward unity, with most having q = M2/M1 < 0.9. This suggests these low-mass systems' dynamical evolution is dominated by migration through circumstellar disks. Our picture of companions spans the entire low-mass main sequence as well as brown dwarfs, showing that formation and dynamical evolution processes mold a continuum of mass all the way beyond the smallest stars.

DOI

https://doi.org/10.57709/35866812

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