Characterizing K2 Candidate Planetary Systems Orbiting Low-mass Stars. IV. Updated Properties for 86 Cool Dwarfs Observed during Campaigns 1-17

• Published in: The Astronomical journal Vol. 158; no. 2; pp. 87 - 119
• Main Authors: Dressing, Courtney D., Hardegree-Ullman, Kevin, Schlieder, Joshua E., Newton, Elisabeth R., Vanderburg, Andrew, Feinstein, Adina D., Duvvuri, Girish M., Arnold, Lauren, Bristow, Makennah, Thackeray, Beverly, Abrahams, Ellianna Schwab, Ciardi, David R., Crossfield, Ian J. M., Yu, Liang, Martinez, Arturo O., Christiansen, Jessie L., Crepp, Justin R., Isaacson, Howard
• Format: Journal Article
• Language: English
• Published: United States The American Astronomical Society 01.08.2019; IOP Publishing
• Subjects: Astronomy; Effective temperatures; Estimates; Extrasolar planets; Infrared spectra; Infrared telescopes; Low mass stars; Massive stars; Metallicity; Near infrared radiation; Parameters; Photometry; Planetary systems; Planets; Properties (attributes); Spectroscopy; stars: fundamental parameters; stars: late-type; stars: low-mass; Target recognition; techniques: photometric; techniques: spectroscopic; Transit; stars: fundamental parameters; planetary systems; stars: low-mass; stars: late-type; techniques: photometric; techniques: spectroscopic
• ISSN: 0004-6256; 0004-637X; 1538-3881
• DOI: 10.3847/1538-3881/ab2895

We present revised stellar properties for 172 K2 target stars that were identified as possible hosts of transiting planets during Campaigns 1-17. Using medium-resolution near-infrared spectra acquired with the NASA Infrared Telescope Facility/SpeX and Palomar/TripleSpec, we found that 86 of our targets were bona fide cool dwarfs, 74 were hotter dwarfs, and 12 were giants. Combining our spectroscopic metallicities with Gaia parallaxes and archival photometry, we derived photometric stellar parameters and compared them to our spectroscopic estimates. Although our spectroscopic and photometric radius and temperature estimates are consistent, our photometric mass estimates are systematically ΔM = 0.11 M (34%) higher than our spectroscopic mass estimates for the least massive stars (M ,phot < 0.4 M ). Adopting the photometric parameters and comparing our results to parameters reported in the Ecliptic Plane Input Catalog, our revised stellar radii are ΔR = 0.15 R (40%) larger, and our revised stellar effective temperatures are roughly ΔTeff = 65 K cooler. Correctly determining the properties of K2 target stars is essential for characterizing any associated planet candidates, estimating the planet search sensitivity, and calculating planet occurrence rates. Even though Gaia parallaxes have increased the power of photometric surveys, spectroscopic characterization remains essential for determining stellar metallicities and investigating correlations between stellar metallicity and planetary properties.