THE K2-ESPRINT PROJECT. II. SPECTROSCOPIC FOLLOW-UP of THREE EXOPLANET SYSTEMS from CAMPAIGN 1 of K2

We report on Doppler observations of three transiting planet candidates that were detected during Campaign 1 of the K2 mission. The Doppler observations were conducted with FIES, HARPS-N and HARPS. We measure the mass of K2-27b (EPIC 201546283b), and provide constraints and upper limits for EPIC 201295312b and EPIC 201577035b. K2-27b is a warm Neptune orbiting its host star in 6.77 days and has a radius of 4.45+0.33−0.33 R⊕ and a mass of 29.1+7.5−7.4 M⊕, which leads to a mean density of 1.80+0.70−0.55 g cm−3. EPIC 201295312b is smaller than Neptune with an orbital period of 5.66 days, radius 2.75+0.24−0.22 R⊕ and we constrain the mass to be below 12 M⊕ at 95% confidence. We also find a long-term trend indicative of another body in the system. EPIC 201577035b, previously confirmed as the planet K2-10b, is smaller than Neptune orbiting its host star in 19.3 days, with radius 3.84+0.35−0.34 R⊕. We determine its mass to be 27+17−16 M⊕, with a 95% confidence uppler limit at 57 M⊕, and mean density 2.6+2.1−1.6 g cm−3. These measurements join the relatively small collection of planets smaller than Neptune with measurements or constraints of the mean density. Our code for performing K2 photometry and detecting planetary transits is now publicly available.