6 research outputs found
Observational constraints on tidal effects using orbital eccentricities
We have analysed radial velocity measurements for known transiting exoplanets
to study the empirical signature of tidal orbital evolution for close-in
planets. Compared to standard eccentricity determination, our approach is
modified to focus on the rejection of the null hypothesis of a circular orbit.
We are using a MCMC analysis of radial velocity measurements and photometric
constraints, including a component of correlated noise, as well as Bayesian
model selection to check if the data justifies the additional complexity of an
eccentric orbit. We find that among planets with non-zero eccentricity values
quoted in the literature, there is no evidence for an eccentricity detection
for the 7 planets CoRoT-5b, WASP-5b, WASP-6b, WASP-10b, WASP-12b, WASP-17b, and
WASP-18b. In contrast, we confirm the eccentricity of HAT-P-16b,
e=0.034\pm0.003, the smallest eccentricity that is reliably measured so far for
an exoplanet as well as that of WASP-14b, which is the planet at the shortest
period (P=2.24 d), with a confirmed eccentricity, e= 0.088\pm0.003. As part of
the study, we present new radial velocity data using the HARPS spectrograph for
CoRoT-1, CoRoT-3, WASP-2, WASP-4, WASP-5 and WASP-7 as well as the SOPHIE
spectrograph for HAT-P-4, HAT-P-7, TrES-2 and XO-2.
We show that the dissipative effect of tides raised in the planet by the star
and vice-versa explain all the eccentricity and spin-orbit alignment
measurements available for transiting planets. We revisit the mass-period
relation (Mazeh et al. 2005, Pont 2011) and consider its relation to the
stopping mechanism of orbital migration for hot Jupiters. In addition to
CoRoT-2 and HD 189733 (Pont 2009), we find evidence for excess rotation of the
star in the systems CoRoT-18, HAT-P-20, WASP-19 and WASP-43.Comment: 31 pages, 17 figures. Accepted by MNRAS (Feb 2012
Determining Eccentricities of Transiting Planets: A Divide in the Mass-Period Plane
The two dominant features in the distribution of orbital parameters for
close-in exoplanets are the prevalence of circular orbits for very short
periods, and the observation that planets on closer orbits tend to be heavier.
The first feature is interpreted as a signature of tidal evolution, while the
origin of the second, a "mass-period relation" for hot Jupiters, is not
understood. In this paper we re-consider the ensemble properties of transiting
exoplanets with well-measured parameters, focussing on orbital eccentricity and
the mass-period relation. We recalculate the constraints on eccentricity in a
homogeneous way, using new radial-velocity data, with particular attention to
statistical biases. We find that planets on circular orbits gather in a
well-defined region of the mass-period plane, close to the minimum period for
any given mass. Exceptions to this pattern reported in the Literature can be
attributed to statistical biases. The ensemble data is compatible with
classical tide theory with orbital circularisation caused by tides raised on
the planet, and suggest that tidal circularisation and the stopping mechanisms
for close-in planets are closely related to each other. The position
mass-period relation is compatible with a relation between a planet's Hill
radius and its present orbit.Comment: 8 pages, to be published in MNRA
Improvements in forecasting intense rainfall: results from the FRANC (forecasting rainfall exploiting new data assimilation techniques and novel observations of convection) project
The FRANC project (Forecasting Rainfall exploiting new data Assimilation techniques and Novel observations of Convection) has researched improvements in numerical weather prediction of convective rainfall via the reduction of initial condition uncertainty. This article provides an overview of the project’s achievements. We highlight new radar techniques: correcting for attenuation of the radar return; correction for beams that are over 90% blocked by trees or towers close to the radar; and direct assimilation of radar reflectivity and refractivity. We discuss the treatment of uncertainty in data assimilation: new methods for estimation of observation uncertainties with novel applications to Doppler radar winds, Atmospheric Motion Vectors, and satellite radiances; a new algorithm for implementation of spatially-correlated observation error statistics in operational data assimilation; and innovative treatment of moist processes in the background error covariance model. We present results indicating a link between the spatial predictability of convection and convective regimes, with potential to allow improved forecast interpretation. The research was carried out as a partnership between University researchers and the Met Office (UK). We discuss the benefits of this approach and the impact of our research, which has helped to improve operational forecasts for convective rainfall event
Orbital eccentricity of WASP-12 and WASP-14 from new radial velocity monitoring with SOPHIE star
International audienceAs part of the long-term radial velocity monitoring of known transiting planets, we have acquired new radial velocity data for the two transiting systems WASP-12 and WASP-14, each harbouring a gas giant on a close orbit (orbital period of 1.09 and 2.24 d, respectively). In both cases, the initial orbital solution suggested a significant orbital eccentricity, 0.049 +/- 0.015 for WASP-12b and 0.091 +/- 0.003 for WASP-14b. Since then, measurements of the occultation of WASP-12 in the infrared have indicated that one projection of the eccentricity (e cos omega) was close to zero, casting doubt on the eccentricity from the initial radial velocity orbit. Our measurements show that the radial velocity data are compatible with a circular orbit. A MCMC analysis taking into account the presence of correlated systematic noise in both the radial velocity and photometric data gives e = 0.017+0.015(-0.010). In contrast, we confirm the orbital eccentricity of WASP-14b, and refine its value to e = 0.0877 +/- 0.0030, a 10 Sigma detection. WASP-14b is thus the closest presently known planet with a confirmed eccentric orbit