Discovery of the secondary eclipse of HAT-P-11 b

TL;DR

This paper reports the first detection of the secondary eclipse of HAT-P-11 b, refining its orbital parameters, measuring its albedo, and discussing temperature variations due to its eccentric orbit.

Contribution

The study provides the first detection of the secondary eclipse of HAT-P-11 b and refines its orbital and physical parameters using Kepler data.

Findings

Secondary eclipse depth of 6.09 ppm detected at 5.5 sigma

Orbital eccentricity precisely measured as 0.26459

Geometric albedo estimated at 0.39, similar to Neptune

Abstract

We report the detection of the secondary eclipse of HAT-P-11 b, a Neptune-sized planet orbiting an active K4 dwarf. Using all available short-cadence data of the Kepler mission, we derive refined planetary ephemeris increasing their precision by more than an order of magnitude. Our simultaneous primary and secondary transit modeling results in improved transit and orbital parameters. In particular, the precise timing of the secondary eclipse allows to pin down the orbital eccentricity to $0.26459_{-0.00048}^{+0.00069}$. The secondary eclipse depth of $6.09_{-1.11}^{+1.12}$ ppm corresponds to a $5.5\sigma$ detection and results in a geometric albedo of $0.39\pm0.07$ for HAT-P-11 b, close to Neptune's value, which may indicate further resemblances between these two bodies. Due to the substantial orbital eccentricity, the planetary equilibrium temperature is expected to change significantly with orbital position and ought to vary between $630^\circ$ K and $950^\circ$ K, depending on the details of heat redistribution in the atmosphere of HAT-P-11 b.