Photometric and spectroscopic detection of the primary transit of the 111-day-period planet HD 80606 b

TL;DR

This paper reports the first detection of the primary transit of the long-period exoplanet HD 80606 b using photometric and spectroscopic methods, refining system parameters and suggesting a possible spin-orbit misalignment.

Contribution

First combined photometric and spectroscopic detection of HD 80606 b's transit, providing key system parameters and evidence for spin-orbit misalignment.

Findings

Transit duration between 9.5 and 17.2 hours

Planetary radius measured as 0.9 ± 0.1 RJup

Possible spin-orbit misalignment indicated

Abstract

We report the detection of the primary transit of the extra-solar planet HD 80606 b, thanks to photometric and spectroscopic observations performed at Observatoire de Haute-Provence, simultaneously with the CCD camera at the 120-cm telescope and the SOPHIE spectrograph at the 193-cm telescope. We observed the whole egress of the transit and partially its central part, in both data sets with the same timings. The ingress occurred before sunset and was not observed. The full duration of the transit was between 9.5 and 17.2 hours. The data allows the planetary radius to be measured (Rp = 0.9 +- 0.1 RJup) and other parameters of the system to be refined. Radial velocity measurements show the detection of a prograde Rossiter-McLaughlin effect, and provide a hint for a spin-orbit misalignment. If confirmed, this misalignment would corroborate the hypothesis that HD 80606 b owes its unusual orbital configuration to Kozai migration. HD 80606 b is by far the transiting planet on the longest period detected today. Its unusually small radius reinforces the observed relationship between the planet radius and the incident flux received from the star and opens new questions for theory. Orbiting a quite bright star (V=9), it opens opportunities to numerous follow-up studies.