TY - JOUR
T1 - An 11 Earth-Mass, Long-Period Sub-Neptune Orbiting a Sun-like Star
AU - Mayo, Andrew W.
AU - Rajpaul, Vinesh M.
AU - Buchhave, Lars A.
AU - Dressing, Courtney D.
AU - Mortier, Annelies
AU - Zeng, Li
AU - Fortenbach, Charles D.
AU - Aigrain, Suzanne
AU - Bonomo, Aldo S.
AU - Cameron, Andrew Collier
AU - Charbonneau, David
AU - Coffinet, Adrien
AU - Cosentino, Rosario
AU - Damasso, Mario
AU - Dumusque, Xavier
AU - Fiorenzano, A. F. Martinez
AU - Haywood, Raphaëlle D.
AU - Latham, David W.
AU - López-Morales, Mercedes
AU - Malavolta, Luca
AU - Micela, Giusi
AU - Molinari, Emilio
AU - Pearce, Logan
AU - Pepe, Francesco
AU - Phillips, David
AU - Piotto, Giampaolo
AU - Poretti, Ennio
AU - Rice, Ken
AU - Sozzetti, Alessandro
AU - Udry, Stephane
N1 - Accepted in AJ, 17 pages, 8 figures, 3 tables
PY - 2019/9/27
Y1 - 2019/9/27
N2 - Although several thousands of exoplanets have now been detected and characterized, observational biases have led to a paucity of long-period, low-mass exoplanets with measured masses and a corresponding lag in our understanding of such planets. In this paper we report the mass estimation and characterization of the long-period exoplanet Kepler-538b. This planet orbits a Sun-like star (V = 11.27) with M_* = 0.892 +/- (0.051, 0.035) M_sun and R_* = 0.8717 +/- (0.0064, 0.0061) R_sun. Kepler-538b is a 2.215 +/- (0.040, 0.034) R_earth sub-Neptune with a period of P = 81.73778 +/- 0.00013 d. It is the only known planet in the system. We collected radial velocity (RV) observations with HIRES on Keck I and HARPS-N on the TNG. We characterized stellar activity by a Gaussian process with a quasi-periodic kernel applied to our RV and cross correlation function full width at half maximum (FWHM) observations. By simultaneously modeling Kepler photometry, RV, and FWHM observations, we found a semi-amplitude of K = 1.68 +/- (0.39, 0.38) m s^-1 and a planet mass of M_p = 10.6 +/- (2.5, 2.4) M_earth. Kepler-538b is the smallest planet beyond P = 50 d with an RV mass measurement. The planet likely consists of a significant fraction of ices (dominated by water ice), in addition to rocks/metals, and a small amount of gas. Sophisticated modeling techniques such as those used in this paper, combined with future spectrographs with ultra high-precision and stability will be vital for yielding more mass measurements in this poorly understood exoplanet regime. This in turn will improve our understanding of the relationship between planet composition and insolation flux and how the rocky to gaseous transition depends on planetary equilibrium temperature.
AB - Although several thousands of exoplanets have now been detected and characterized, observational biases have led to a paucity of long-period, low-mass exoplanets with measured masses and a corresponding lag in our understanding of such planets. In this paper we report the mass estimation and characterization of the long-period exoplanet Kepler-538b. This planet orbits a Sun-like star (V = 11.27) with M_* = 0.892 +/- (0.051, 0.035) M_sun and R_* = 0.8717 +/- (0.0064, 0.0061) R_sun. Kepler-538b is a 2.215 +/- (0.040, 0.034) R_earth sub-Neptune with a period of P = 81.73778 +/- 0.00013 d. It is the only known planet in the system. We collected radial velocity (RV) observations with HIRES on Keck I and HARPS-N on the TNG. We characterized stellar activity by a Gaussian process with a quasi-periodic kernel applied to our RV and cross correlation function full width at half maximum (FWHM) observations. By simultaneously modeling Kepler photometry, RV, and FWHM observations, we found a semi-amplitude of K = 1.68 +/- (0.39, 0.38) m s^-1 and a planet mass of M_p = 10.6 +/- (2.5, 2.4) M_earth. Kepler-538b is the smallest planet beyond P = 50 d with an RV mass measurement. The planet likely consists of a significant fraction of ices (dominated by water ice), in addition to rocks/metals, and a small amount of gas. Sophisticated modeling techniques such as those used in this paper, combined with future spectrographs with ultra high-precision and stability will be vital for yielding more mass measurements in this poorly understood exoplanet regime. This in turn will improve our understanding of the relationship between planet composition and insolation flux and how the rocky to gaseous transition depends on planetary equilibrium temperature.
KW - astro-ph.EP
U2 - 10.3847/1538-3881/ab3e2f
DO - 10.3847/1538-3881/ab3e2f
M3 - Article
SN - 0004-6256
JO - Astronomical Journal
JF - Astronomical Journal
ER -