Author ORCID Identifier

0000-0003-4568-2079

Date of Award

8-8-2023

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Physics and Astronomy

First Advisor

Todd J. Henry

Second Advisor

Russel J. White

Third Advisor

Douglas R. Gies

Fourth Advisor

Eric E. Mamajek

Abstract

We present the results of a spectroscopic study to determine the stellar properties, activity levels, space motions, and ages of the nearest K dwarfs. The targeted stars are members of RKSTAR (RECONS K Star) Survey that includes ∼5000 K dwarf primaries within 50 pc. An initial study established a benchmark calibration set of 35 K dwarfs with known ages of 20 Myr to 5 Gyr and high resolution (R=80000) spectra acquired on the CHIRON echelle spectrometer on the SMARTS 1.5m telescope at CTIO. Two known spectral indicators of activity and youth — the Hα absorption line (6562.8 Å) and the Li I resonance line (6707.8 Å) — showed strong trends in the training set. A sample of 615 K dwarfs within 33 parsecs and found between declinations +30 and −30 degrees has now been observed with CHIRON and analyzed relative to the stars in the benchmark calibration set. Surprisingly, it appears that as many as ∼8% of these K dwarfs have spectroscopic features indicating that they are young and/or active. As expected, Galactic U V W space motions indicate that most of the stars fall into the thin (80%) and thick (20%) disk populations, with a single outlier, HD 134439, which is a known halo star. Overall, we find a set of metal poor K dwarfs with [Fe/H]values of −0.5 dex or less that account for 4% of the population in the solar neighborhood.

Empirical SpecMatch has been used to measure stellar properties for this sample of K dwarfs: temperatures range from 3600–5500 K, metallicities range from −0.6 < [Fe/H]< +0.55, and rotational velocities (v sin i) range from less than 10 km/s to more than 50 km/s. Surface gravity values (log g values) have also been determined, although they are less reliable than the other quantities. Cross-matching with NASA’s Exoplanet Archive reveals that only 42 exoplanet host stars are among our sample, highlighting the limited focus on mid and late-type K dwarfs (Teff < 4800 K) in large exoplanet surveys. As a result of this work, we have identified 500 K dwarfs that are calm host stars worthy of detailed efforts to detect terrestrial planets. This work will serve as a key resource for assessing host star suitability for exoplanet habitability.

DOI

https://doi.org/10.57709/35868249

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