# Characterizing K2 Candidate Planetary Systems Orbiting Low-Mass Stars IV: Updated Properties for 86 Cool Dwarfs Observed During Campaigns 1-17

## TL;DR

This study refines stellar properties of 172 K2 target stars, emphasizing the importance of spectroscopic data for accurate characterization of planet-hosting stars and their planetary systems.

## Contribution

It provides updated stellar parameters for 86 cool dwarfs, combining spectroscopic and photometric data, and highlights discrepancies between different estimation methods.

## Key findings

- Spectroscopic and photometric radius and temperature estimates are consistent.
- Photometric mass estimates are systematically higher than spectroscopic estimates for low-mass stars.
- Revised stellar radii are 0.15 solar radii larger, and temperatures are roughly 65K cooler.

## Abstract

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 0.11 solar masses (34%) higher than our spectroscopic mass estimates for the least massive stars (photometric mass estimates < 0.4 solar masses). Adopting the photometric parameters and comparing our results to parameters reported in the Ecliptic Plane Input Catalog, our revised stellar radii are 0.15 solar radii (40%) larger and our revised stellar effective temperatures are roughly 65K 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.