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A Kinematic and Spectroscopic Analysis of the Nearest K Dwarfs

Presentation #208.04 in the session Fundamental Properties I.

Published onJun 29, 2022
A Kinematic and Spectroscopic Analysis of the Nearest K Dwarfs

We report systemic and UVW space velocities for 42 key K dwarf systems for which we have acquired spectra (R=80,000) using the CHIRON high-resolution echelle spectrometer on the SMARTS 1.5m telescope at CTIO. The sample described here includes 35 systems in a benchmark sample divided into five subsets with reliable age estimates of 20 million years to a few billion years, plus seven additional K dwarf systems selected from a sample of several hundred field stars because they have variable systemic gamma velocity (GV) measurements. These curious discoveries are compared to our benchmark set by using the measured GVs and Gaia data to determine UVW space motions through the Galaxy. The observed stars are part of a large RECONS (REsearch Consortium On Nearby Stars, effort to explore more than 1,200 of the nearest K dwarfs, all within 50 pc.

We confirm that 25 of the 35 systems in the benchmark sample are, indeed, members of moving groups and open clusters using their UVW motions and four spectral features associated with youth and activity. We find that PX Vir, a proposed member of the AB Doradus moving group, should be reclassified as a field star. Of the remaining nine systems, four are in fact field stars and five fall well outside the supposed membership ellipses produced in our UVW diagrams, with the latter having RECONS GVs measured that do not match Gaia’s. Overall, our GVs ranged from -54 km/s to +44 km/s, typical of stars in the local part of the Milky Way. All seven stars with initial GV measurements that appeared to change were confirmed to vary, likely due to surface activity affecting the spectral lines used for the GV measurements, and not due to companions.

The benchmark set described here provides templates for our next step in evaluating the nearest K dwarfs — a sample of 287 K dwarf systems within 25 pc of the Sun that lie in the equatorial region of the celestial sphere, between declinations +30 and -30 degrees. Ultimately, our study aims to use diagnostics of age, activity, and kinematics, along with spectroscopically-derived stellar properties to identify the best K dwarfs for habitable planetary companions.

This effort has been supported by the NSF through grants AST-1517413 and AST-1910130 via observations made possible by the SMARTS Consortium.

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