Exoplanets down to the size of Earth have been found, but not in the habitable zone--that is, at a distance from the parent star at which water, if present, would be liquid. There are planets in the ...habitable zone of stars cooler than our Sun, but for reasons such as tidal locking and strong stellar activity, they are unlikely to harbour water-carbon life as we know it. The detection of a habitable Earth-mass planet orbiting a star similar to our Sun is extremely difficult, because such a signal is overwhelmed by stellar perturbations. Here we report the detection of an Earth-mass planet orbiting our neighbour star α Centauri B, a member of the closest stellar system to the Sun. The planet has an orbital period of 3.236 days and is about 0.04 astronomical units from the star (one astronomical unit is the Earth-Sun distance).
Context.
It is common practice to claim the detection of a signal if, for a certain statistical significance metric, the signal significance exceeds a certain threshold fixed in advance. In the ...context of exoplanet searches in radial velocity data, the most common statistical significance metrics are the Bayes factor and the false alarm probability (FAP). Both criteria have proved useful, but do not directly address whether an exoplanet detection should be claimed. Furthermore, it is unclear which detection threshold should be taken and how robust the detections are to model misspecification.
Aims.
The aim of the present work is to define a detection criterion that conveys as precisely as possible the information needed to claim an exoplanet detection, as well as efficient numerical methods to compute it. We compare this new criterion to existing ones in terms of sensitivity and robustness to a change in the model.
Methods.
We define a general detection criterion called the false inclusion probability (FIP). In the context of exoplanet detections it provides the posterior probability of presence of a planet with a period in a certain interval. Posterior distributions are computed with the nested sampling package
POLYCHORD
. We show that for FIP and Bayes factor calculations, defining priors on linear parameters as Gaussian mixture models can significantly speed up computations. The performance of the FAP, Bayes factor, and FIP are studied via simulations and analytical arguments. We compare the methods assuming the model is correct, then evaluate their sensitivity to the prior and likelihood choices.
Results.
Among other properties, the FIP offers ways to test the reliability of the significance levels; it is a particularly efficient way to account for aliasing, and it allows the presence of planets to be excluded with a certain confidence. In our simulations, we find that the FIP outperforms existing detection metrics. We show that low amplitude planet detections are sensitive to priors on period and semi-amplitude, which will require further attention for the detection of Earth-like planets. We recommend to let the parameters of the noise model free in the analysis, rather than fixing a noise model based on a fit to ancillary indicators.
ABSTRACT While the vast majority of multiple-planet systems have orbital angular momentum axes that align with the spin axis of their host star, Kepler-56 is an exception: its two transiting planets ...are coplanar yet misaligned by at least 40° with respect to the rotation axis of their host star. Additional follow-up observations of Kepler-56 suggest the presence of a massive, non-transiting companion that may help explain this misalignment. We model the transit data along with Keck/HIRES and HARPS-N radial velocity data to update the masses of the two transiting planets and infer the physical properties of the third, non-transiting planet. We employ a Markov Chain Monte Carlo sampler to calculate the best-fitting orbital parameters and their uncertainties for each planet. We find the outer planet has a period of 1002 5 days and minimum mass of 5.61 0.38 M Jup . We also place a 95% upper limit of 0.80 m s−1 yr−1 on long-term trends caused by additional, more distant companions.
We introduce the BEBOP radial velocity survey for circumbinary planets. We initiated this survey using the CORALIE spectrograph on the Swiss
Euler
Telescope at La Silla, Chile. An intensive four-year ...observation campaign commenced in 2013, targeting 47 single-lined eclipsing binaries drawn from the EBLM survey for low mass eclipsing binaries. Our specific use of binaries with faint M dwarf companions avoids spectral contamination, providing observing conditions akin to single stars. By combining new BEBOP observations with existing ones from the EBLM programme, we report on the results of 1519 radial velocity measurements over timespans as long as eight years. For the best targets we are sensitive to planets down to 0.1
M
Jup
, and our median sensitivity is 0.4
M
Jup
. In this initial survey we do not detect any planetary mass companions. Nonetheless, we present the first constraints on the abundance of circumbinary companions, as a function of mass and period. A comparison of our results to
Kepler
’s detections indicates a dispersion of planetary orbital inclinations less than ~10°.
We report the detection of a transiting planet around π Men (HD 39091), using data from the Transiting Exoplanet Survey Satellite (TESS). The solar-type host star is unusually bright (V = 5.7) and ...was already known to host a Jovian planet on a highly eccentric, 5.7 yr orbit. The newly discovered planet has a size of 2.04 0.05 R⊕ and an orbital period of 6.27 days. Radial-velocity data from the High-Accuracy Radial-velocity Planet Searcher and Anglo-Australian Telescope/University College London Echelle Spectrograph archives also displays a 6.27 day periodicity, confirming the existence of the planet and leading to a mass determination of 4.82 0.85 M⊕. The star's proximity and brightness will facilitate further investigations, such as atmospheric spectroscopy, asteroseismology, the Rossiter-McLaughlin effect, astrometry, and direct imaging.
The EBLM Project Triaud, Amaury H. M. J.; Martin, David V.; Ségransan, Damien ...
Astronomy and astrophysics (Berlin),
12/2017, Letnik:
608
Journal Article
PDF
