A Warm Neptune Orbiting the Nearby Active mid M dwarf TOI-2015 and Precision Spectral Parameters in the Near-Infrared with HPF-SpecMatch

Abstract

We report on the discovery and characterization of a warm Neptune orbiting the nearby (d=47.3pc) mid M dwarf TOI-2015. We characterize the properties of the planet using TESS photometry, precision near-infrared RVs with the Habitable-zone Planet Finder (HPF) Spectrograph, precision diffuser-assisted ground-based photometry, and high contrast imaging. Using the HPF-SpecMatch spectral matching code, the star has an effective temperature of 3193K. The planet has a radius of R=3.37+/-.20 stellar radii and a mass of M = 12.0 +/- 5.2 stellar masses and we find that its bulk density is compatible with a ~6% H/He gaseous envelope enveloping a rocky core. The star is rapidly rotating with a rotation period of Prot = 6.0 +/- 0.6 days, making the planet one of few M dwarf planets amenable for obliquity constraints via the Rossiter-McLaughlin effect. Due to the large transit depth and the relative brightness of the star at near-infrared wavelengths (J=11.3), the planet is a promising target for atmospheric characterization in the future with JWST. We publicly release a code we call HPF-SpecMatch to calculate accurate stellar parameters from as-observed near-infrared HPF spectra of 170 stars and describe its performance.