A Multi-planet System Transiting the V = 9 Rapidly Rotating F-Star HD 106315

We report the discovery of a multi-planet system orbiting HD 106315, a rapidly rotating mid F-type star, using data from the K2 mission. HD 106315 hosts a 2.51 ± 0.12 R _⊕ sub-Neptune in a 9.5-day orbit and a {4.31}_-0.27^+0.24 {R}_\oplus super-Neptune in a 21-day orbit. The projected rotational velocity of HD 106315 (12.9 km s^-1) likely precludes precise measurements of the planets’ masses but could enable a measurement of the sky-projected spin-orbit obliquity for the outer planet via Doppler tomography. The eccentricities of both planets were constrained to be consistent with 0, following a global modeling of the system that includes a Gaia distance and dynamical arguments. The HD 106315 system is one of few multi-planet systems hosting a Neptune-sized planet for which orbital obliquity measurements are possible, making it an excellent test-case for formation mechanisms of warm-Neptunian systems. The brightness of the host star also makes HD 106315 c a candidate for future transmission spectroscopic follow-up studies.