Planets and Stellar Activity: Hide and Seek in the CoRoT-7 system

Abstract

Since the discovery of the transiting Super-Earth CoRoT-7b, several investigations have been made of the number and precise masses of planets present in the system, but they all yield different results, owing to the star's high level of activity. Radial velocity (RV) variations induced by stellar activity therefore need to be modelled and removed to allow a reliable detection of all planets in the system. We re-observed CoRoT-7 in January 2012 with both HARPS and the CoRoT satellite, so that we now have the benefit of simultaneous RV and photometric data. We fitted the off-transit variations in the CoRoT lightcurve using a harmonic decomposition similar to that implemented in Queloz et al. (2009). This fit was then used to model the stellar RV contribution, according to the methods described by Aigrain et al. (2011). This model was incorporated into a Monte Carlo Markov Chain in order to make a precise determination of the orbits of CoRoT-7b and CoRoT-7c. We also assess the evidence for the presence of one or two additional planetary companions.

The Astrobiology Primer v2.0

“…Other observations, such as measurements of changes to the timing of transits in multiplanet systems (“transit-timing variations”) can also constrain the mass. There are nine super-Earths with good determinations of both their radius and mass: GJ 1214 b (Charbonneau et al , 2009 ), 55 Cnc e (Gillon et al , 2012 ; Nelson et al , 2014 ), Kepler-36b (Carter et al , 2012 ), HD 97658 b (Dragomir et al , 2013 ), CoRoT-7b (Barros et al , 2014 ; Haywood et al , 2014 ), HIP 116454 b (Vanderburg et al , 2015 ), Kepler-78b (Howard et al , 2013 ; Pepe et al , 2013 ), and Kepler-10b and 10c (Dumusque et al , 2014 ).…”

Dynamical masses of two infant giant planets

“…δ τ is the Kronecker delta function, and τ represents an interval between two measurements, t − t . This kernel behaves similar to the classical quasi-periodic kernel 28 , with an explicit mode at the first harmonic of the rotation period (PQP2 from now on). A simpler version of this kernel was successfully used to to model the variations of Proxima Centauri to the level of the instrumental precision 26 .…”

“…The model uses the K2 photometry to constrain the planetary orbital periods, phases and radii, the LCOGT photometry and the RVs to constrain the timescales and amplitudes of the activity variations during our observing campaign, and the RVs to measure the masses of the planets. To model the activity components, we relied on a Gaussian processes (GP) regression 27,28 . Given the complexity of the activity variations, we tested several GP kernels.…”

Thermodynamics, Disequilibrium, Evolution: Far-From-Equilibrium Geological and Chemical Considerations for Origin-Of-Life Research

“…However, even this small subpopulation of rocky worlds shows a remarkable diversity, ranging from "dense and hot" exoplanets close to their parent star, with planetary surface temperatures greater than 2000 K (e.g. Corot 7b (Barros et al 2014 ;Haywood et al 2014 ), Kepler 10b (Dumusque et al 2014 ), 55 Cnc e (Gillon et al 2012 ;Nelson et al 2014 ) and the disintegrating planet Kepler-78b (Pepe et al 2013 ;Howard et al 2013 )), to "less dense and cool" exoplanets with densities that make them prospective wet rocky worlds (such as GJ 1214b (Charbonneau et al 2009 ) and HD97658b (Dragomir et al 2013 )). …”