Author ORCID Identifier


Date of Award


Degree Type


Degree Name

Doctor of Philosophy (PhD)


Physics and Astronomy

First Advisor

Todd J. Henry

Second Advisor

Sébastien Lépine

Third Advisor

Andrew W. Mann

Fourth Advisor

Brian D. Thoms

Fifth Advisor

Russel J. White


We present the Systematic Investigation of Radii and Environments of Nearby Stars (SIRENS) Project: the characterization of 1593 stars including 1504 nearby red dwarfs within 25 parsecs. The primary goal is to provide radii for the all-sky sample of red dwarf single stars and spatially resolved primaries with accurate, pre-Gaia, trigonometric parallaxes placing them within 25 parsecs, with a special focus on the understudied late-type M dwarfs that have rarely been resolved with optical or infrared long-baseline interferometers. We provide Johnson-Kron-Cousins VRI, 2MASS JHK, and WISE W1W2W3 photometry for a total of 1593 stars, including new/updated VRI photometry for 637 stars observed at the CTIO/SMARTS 0.9m, ARCSAT 0.5m, and KPNO/WIYN 0.9m. We combine the distances and photometry and apply spectral energy distribution model fitting similar to the methodology outlined by Dieterich et al. (2014) to determine fundamental parameters — temperature, luminosity, and radius — for the sample. Comparison of our results for 26 stars to their radii determined using interferometry indicates a median absolute difference of only 6%. The result is a set of fundamental parameters for a comprehensive all-sky sample of red dwarfs spanning an unprecedented range of red dwarf spectral types, from approximately M0 to the end of the stellar main sequence. We reveal trends in the dispersion and slope of the radius-effective temperature relationship of red dwarfs and link these trends to star spot coverage. We demonstrate that the radius of a star at effective temperatures greater than 2850 K can span a ~0.35 R range; an effective temperature-radius relation cannot be used to accurately or precisely calculate either of these parameters without additional information. We compare the core main sequence sample of 1503 primary stars and Proxima Centauri to control samples of 53 pre-main sequence stars and 36 cool subdwarfs to map the wide 0.06-1.08 R range in radii for red dwarfs and their young and old counterparts, with the tiniest subdwarf found to be 3/4 the size of Saturn, and the smallest dwarf just smaller than Saturn. We use large radii to identify 56 new young star candidates and small radii to identify 31 cool subdwarf candidates within 25 parsecs. We emphasize that the data required for our technique are photometry and parallaxes only, and form the basis for a much larger future effort using Gaia data combined with infrared data for low-mass stars over the entire sky.

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