The changing phases of extrasolar planet CoRoT-1b

TL;DR

This paper analyzes optical photometric data of the hot Jupiter CoRoT-1b over 36 orbits, revealing a nearly black nightside and a dominant dayside flux with low reflectivity, enhancing understanding of its phase variations.

Contribution

It provides the first optical phase curve analysis of CoRoT-1b, showing its nightside is dark and quantifying its low geometric albedo, which was previously unmeasured.

Findings

Nightside hemisphere is consistent with being entirely black.

Dayside flux dominates the optical phase curve.

Geometric albedo is less than 0.20.

Abstract

Hot Jupiters are a class of extrasolar planet that orbit their parent stars at very short distances. Due to their close proximity, they are expected to be tidally locked, which can lead to a large temperature difference between their day and nightsides. Infrared observations of eclipsing systems have yielded dayside temperatures for a number of transiting planets. Furthermore the day-night contrast of the transiting extrasolar planet HD 189733b was mapped using infrared observations. It is expected that the contrast between the dayside and nightside of hot Jupiters is much higher at visual wavelengths as we move shortward of the peak emission, and could be further enhanced by reflected stellar light. Here we report on the analysis of optical photometric data of the transiting hot Jupiter CoRoT-1b, which cover 36 planetary orbits. The nightside hemisphere of the planet is consistent with being entirely black, with the dayside flux dominating the optical phase curve. This means that at optical wavelengths the planet's phase variation is just as we see it for the interior planets in our own solar system. The data allow only for a small fraction of reflected light, corresponding to a geometric albedo <0.20.