Aims. We attempt to increase the number of trans-Neptunian objects (TNOs) whose short-term variability has been studied and compile a high quality database with the least possible biases, which may be used to perform statistical analyses. Methods. We performed broadband CCD photometric observations using several telescopes (the 1.5 m telescope at Sierra Nevada Observatory, the 2.2 m Calar Alto telescope and the 2.5 m INT on La Palma).Results. We present the results of 6 years of observations, reduced and analyzed with the same tools in a systematic way. We report completely new data on 15 objects, for 5 objects we present a new analysis of previously published results plus additional data and for 9 objects we present a new analysis of data already published. Lightcurves, possible rotation periods, and photometric amplitudes are reported for all of them. The photometric variability is smaller than previously thought: the mean amplitude of our sample is 0.1 mag and only around 15% of our sample has a larger variability than 0.15 mag. The smaller variability seems to be caused by a bias of previous observations. We find a very weak trend of faster spinning objects towards smaller sizes, which appears to be consistent with the smaller objects being more collisionally evolved, but may also be a specific feature of the Centaurs, the smallest objects in our sample. We also find that the smaller the objects, the larger their amplitude, which is also consistent with the idea that small objects are more collisionally evolved and thus more deformed. Average rotation rates from our work are 7.5 h for the whole sample, 7.6 h for the TNOs alone and 7.3 h for the Centaurs. Maxwellian fits to the period distribution yield similar results.
Surveys have shown that super-Earth and Neptune-mass exoplanets are more frequent than gas giants around low-mass stars, as predicted by the core accretion theory of planet formation. We report the discovery of a giant planet around the very-low-mass star GJ 3512, as determined by optical and near-infrared radial-velocity observations. The planet has a minimum mass of 0.46 Jupiter masses, very high for such a small host star, and an eccentric 204-day orbit. Dynamical models show that the high eccentricity is most likely due to planet-planet interactions. We use simulations to demonstrate that the GJ 3512 planetary system challenges generally accepted formation theories, and that it puts constraints on the planet accretion and migration rates. Disk instabilities may be more efficient in forming planets than previously thought.
Context. We present an extensive ground-based photometric and spectroscopic campaign of the γ Dor CoRoT target HD 49434. This campaign was a preparatory step of the CoRoT satellite observations, which occurred between October 2007 and March 2008. Aims. With satellite data, detection of low-degree pulsation modes only is achievable, and, as no filters are available, with poor identification. Ground-based data promise eventually to identify additional modes and provide extra input for the identification: spectroscopic data allows the detection of high-degree modes and an estimate of the azimuthal number m. We attempt to detect and identify as many pulsation modes as possible from the ground-based dataset of the γ Dor star HD 49434, and anticipate the CoRoT results. Methods. We searched for frequencies in the multi-colour variations, the pixel-to-pixel variations across the line profiles, and the moments variations in a large dataset, consisting of both multi-colour photometric and spectroscopic data from different observatories, using different frequency analysis methods. We performed a tentative mode identification of the spectroscopic frequencies using the Moment Method and the Intensity Period Search Method. We also completed an abundance analysis. Results. The frequency analysis clearly indicates the presence of four frequencies in the 0.2−1.7 d −1 interval, as well as six frequencies in the 5−12 d −1 domain. The low frequencies are typical of γ Dor variables, while the high frequencies are common to δ Sct pulsators. We propose that the frequency 2.666 d −1 is the rotational frequency. All modes, for which an identification was possible, appear to be high-degree modes (3 ≤ ≤ 8). We did not find evidence for a possible binary nature of the star HD 49434. The element abundances that we derived are consistent with values obtained in previous analyses. Conclusions. We classify the γ Dor star HD 49434 as a hybrid pulsator, which pulsates simultaneously in p-and g-modes. This implies that HD 49434 is an extremely interesting target for asteroseismic modelling.
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