# Two Small Transiting Planets and a Possible Third Body Orbiting HD 106315

## TL;DR

This paper reports the discovery of two small transiting exoplanets and evidence for a third body orbiting the bright star HD 106315, highlighting its suitability for detailed follow-up studies of planetary properties and system architecture.

## Contribution

The study presents the detection of two transiting planets and a possible third companion around HD 106315, demonstrating the potential for detailed characterization of such systems.

## Key findings

- Two transiting planets with radii of 2.23 and 3.95 R_Earth identified.
- Radial velocity trend suggests a third body with period >160 days and mass >45 M_Earth.
- HD 106315 is an excellent target for future mass, density, and atmospheric studies.

## Abstract

The masses, atmospheric makeups, spin-orbit alignments, and system architectures of extrasolar planets can be best studied when the planets orbit bright stars. We report the discovery of three bodies orbiting HD 106315, a bright (V = 8.97 mag) F5 dwarf targeted by our K2 survey for transiting exoplanets. Two small, transiting planets have radii of 2.23 (+0.30/-0.25) R_Earth and 3.95 (+0.42/-0.39) R_Earth and orbital periods of 9.55 d and 21.06 d, respectively. A radial velocity (RV) trend of 0.3 +/- 0.1 m/s/d indicates the likely presence of a third body orbiting HD 106315 with period >160 d and mass >45 M_Earth. Transits of this object would have depths of >0.1% and are definitively ruled out. Though the star has v sin i = 13.2 km/s, it exhibits short-timescale RV variability of just 6.4 m/s, and so is a good target for RV measurements of the mass and density of the inner two planets and the outer object's orbit and mass. Furthermore, the combination of RV noise and moderate v sin i makes HD 106315 a valuable laboratory for studying the spin-orbit alignment of small planets through the Rossiter-McLaughlin effect. Space-based atmospheric characterization of the two transiting planets via transit and eclipse spectroscopy should also be feasible. This discovery demonstrates again the power of K2 to find compelling exoplanets worthy of future study.