Multi-season optical modulation phased with the orbit of the super-Earth 55 Cancri e

Sulis, S.; Dragomir, D.; Lendl, M.; Bourrier, V.; Demory, B. O.; Fossati, L.; Cubillos, P. E.; Guenther, D. B.; Kane, S. R.; Kuschnig, R.; Matthews, J. M.; Moffat, A. F. J.; Rowe, J. F.; Sasselov, D.; Weiss, W. W.; Winn, J. N. (2019). Multi-season optical modulation phased with the orbit of the super-Earth 55 Cancri e. Astronomy and astrophysics, 631(A129), A129. EDP Sciences 10.1051/0004-6361/201936066

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Context. 55 Cnc e is a transiting super-Earth orbiting a solar-like star with an orbital period of ~17.7 h. In 2011, using the Microvariability and Oscillations in Stars (MOST) space telescope, a quasi-sinusoidal modulation in flux was detected with the same period as the planetary orbit. The amplitude of this modulation was too large to be explained as the change in light reflected or emitted by the planet.

Aims. The MOST telescope continued to observe 55 Cnc e for a few weeks per year over five years (from 2011 to 2015), covering 143 individual transits. This paper presents the analysis of the observed phase modulation throughout these observations and a search for the secondary eclipse of the planet.

Methods. The most important source of systematic noise in MOST data is due to stray-light reflected from the Earth, which is modulated with both the orbital period of the satellite (101.4 min) and the Earth’s rotation period. We present a new technique to deal with this source of noise, which we combined with standard detrending procedures for MOST data. We then performed Markov chain Monte Carlo analyses of the detrended light curves, modeling the planetary transit and phase modulation.

Results. We find phase modulations similar to those seen in 2011 in most of the subsequent years; however, the amplitude and phase of maximum light are seen to vary, from year to year, from 113 to 28 ppm and from 0.1 to 3.8 rad. The secondary eclipse is not detected, but we constrain the geometric albedo of the planet to less than 0.47 (2σ).

Conclusions. While we cannot identify a single origin of the observed optical modulation, we propose a few possible scenarios. Those include star-planet interaction, such as coronal rains and spots rotating with the motion of the planet along its orbit, or the presence of a transiting circumstellar torus of dust. However, a detailed interpretation of these observations is limited by their photometric precision. Additional observations at optical wavelengths could measure the variations at higher precision, contribute to uncovering the underlying physical processes, and measure or improve the upper limit on the albedo of the planet.

Item Type:

Journal Article (Original Article)


08 Faculty of Science > Physics Institute > Space Research and Planetary Sciences
08 Faculty of Science > Physics Institute
10 Strategic Research Centers > Center for Space and Habitability (CSH)
08 Faculty of Science > Physics Institute > NCCR PlanetS

UniBE Contributor:

Demory, Brice-Olivier


500 Science
500 Science > 520 Astronomy
500 Science > 530 Physics




EDP Sciences




Danielle Zemp

Date Deposited:

14 Apr 2020 14:29

Last Modified:

19 Apr 2020 02:53

Publisher DOI:





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