Using HARPS-N to characterise the long-period planets in the PH-2 and Kepler-103 systems
2019
We present confirmation of the planetary nature of PH-2b, as well as the first mass estimates for the two
planetsin the
Kepler-103 system. PH-2b and
Kepler-103c are both long-period and transiting, a sparsely-populated category of
exoplanet. We use {\it
Kepler} light-curve data to estimate a radius, and then use
HARPS-N radial velocities to determine the semi-amplitude of the stellar reflex motion and, hence, the
planetmass. For PH-2b we recover a 3.5-$\sigma$ mass estimate of $M_p = 109^{+30}_{-32}$ M$_\oplus$ and a radius of $R_p = 9.49\pm0.16$ R$_\oplus$. This means that PH-2b has a
Saturn-like bulk density and is the only
planetof this type with an
orbital period$P > 200$ days that orbits a single star. We find that
Kepler-103b has a mass of $M_{\text{p,b}} = 11.7^{+4.31}_{-4.72}$ M$_{\oplus}$ and
Kepler-103c has a mass of $M_{\text{p,c}} = 58.5^{+11.2}_{-11.4}$ M$_{\oplus}$. These are 2.5$\sigma$ and 5$\sigma$ results, respectively. With radii of $R_{\text{p,b}} = 3.49^{+0.06}_{-0.05}$ R$_\oplus$, and $R_{\text{p,c}} = 5.45^{+0.18}_{-0.17}$ R$_\oplus$, these results suggest that
Kepler-103b has a
Neptune-like density, while
Kepler-103c is one of the highest density
planetswith a period $P > 100$ days. By providing high-precision estimates for the masses of the long-period, intermediate-mass
planetsPH-2b and
Kepler-103c, we increase the sample of long-period
planetswith known masses and radii, which will improve our understanding of the mass-radius relation across the full range of
exoplanetmasses and radii.
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