9 research outputs found

    A system of three transiting super-Earths in a cool dwarf star

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    We present the detection of three super-Earths transiting the cool star LP415-17, monitored by K2 mission in its 13th campaign. High resolution spectra obtained with HARPS-N/TNG showed that the star is a mid-late K dwarf. Using spectral synthesis models we infer its effective temperature, surface gravity and metallicity and subse- quently determined from evolutionary models a stellar radius of 0.58 R Sun. The planets have radii of 1.8, 2.6 and 1.9 R Earth and orbital periods of 6.34, 13.85 and 40.72 days. High resolution images discard any significant contamination by an intervening star in the line of sight. The orbit of the furthest planet has radius of 0.18 AU, close to the inner edge of the habitable zone. The system is suitable to improve our understanding of formation and dynamical evolution of super-Earth systems in the rocky - gaseous threshold, their atmospheres, internal structure, composition and interactions with host stars.Comment: Accepted for publication in MNRAS Letter

    Gliese 49: activity evolution and detection of a super-Earth A HADES and CARMENES collaboration

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    Small planets around low-mass stars often show orbital periods in a range that corresponds to the temperate zones of their host stars which are therefore of prime interest for planet searches. Surface phenomena such as spots and faculae create periodic signals in radial velocities and in observational activity tracers in the same range, so they can mimic or hide true planetary signals. We aim to detect Doppler signals corresponding to planetary companions, determine their most probable orbital configurations, and understand the stellar activity and its impact on different datasets. We analyze 22 years of data of the M1.5V-type star Gl49 (BD+61 195) including HARPS-N and CARMENES spectrographs, complemented by APT2 and SNO photometry. Activity indices are calculated from the observed spectra, and all datasets are analyzed with periodograms and noise models. We investigate how the variation of stellar activity imprints on our datasets. We further test the origin of the signals and investigate phase shifts between the different sets. To search for the best-fit model we maximize the likelihood function in a Markov Chain Monte Carlo approach. As a result of this study, we are able to detect the super-Earth Gl49b with a minimum mass of 5.6 Ms. It orbits its host star with a period of 13.85d at a semi-major axis of 0.090 au and we calculate an equilibrium temperature of 350 K and a transit probability of 2.0%. The contribution from the spot-dominated host star to the different datasets is complex, and includes signals from the stellar rotation at 18.86d, evolutionary time-scales of activity phenomena at 40-80d, and a long-term variation of at least four years

    The First Post-Kepler Brightness Dips of KIC 8462852

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    HADES RV programme with HARPS-N at TNG: XII. The abundance signature of M dwarf stars with planets

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    Context. Most of our current knowledge on planet formation is still based on the analysis of main sequence, solar-type stars. Conversely, detailed chemical studies of large samples of M dwarfs hosting planets are still missing. Aims. Correlations exist between the presence of different types of planets around FGK stars and metallicity, individual chemical abundance, and stellar mass. We aim to test whether or not these correlations still hold for the less-massive M dwarf stars. Methods to determine stellar abundances of M dwarfs from high-resolution optical spectra in a consistent way are still missing. The present work is a first attempt to fill this gap. Methods. We analyse a large sample of M dwarfs with and without known planetary companions in a coherent and homogeneous way. We develop for the first time a methodology to determine stellar abundances of elements other than iron for M dwarf stars from high-resolution optical spectra. Our methodology is based on the use of a principal component analysis and sparse Bayesian methods. We made use of a set of M dwarfs orbiting around an FGK primary with known abundances to train our methods. We applied our methods to derive stellar metalliticies and abundances of a large sample of M dwarfs observed within the framework of current radial-velocity surveys. We then used a sample of nearby FGK stars to cross-validate our technique by comparing the derived abundance trends in the M dwarf sample with those found on the FGK stars. Results. The metallicity distribution of the different subsamples reveals a correlation between the metallicities of M dwarfs and their probability of hosting giant planets. We also find a correlation between this latter probability and stellar mass. M dwarfs hosting low-mass planets do not seem to follow the so-called planet-metallicity correlation. We also find that the frequency of low-mass planets does not depend on the mass of the stellar host. These results appear to be in agreement with those of previous works. However, we note that for giant-planet hosts our metallicities predict a weaker planet-host metallicity correlation but a stronger mass-dependency than corresponding values derived from photometric results. We show for the first time that there seems to be no differences between M dwarfs with and without known planets in terms of their abundance distributions of elements different from iron. Conclusions. Our data show that low-mass stars with planets follow the same metallicity, mass, and abundance trends as their FGK counterparts, which are usually explained within the framework of core-accretion models

    Rapid contraction of giant planets orbiting the 20-million-year-old star V1298 Tau

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    Current theories of planetary evolution predict that infant giant planets have large radii and very low densities before they slowly contract to reach their final size after about several hundred million years1,2. These theoretical expectations remain untested so far as the detection and characterization of very young planets is extremely challenging due to the intense stellar activity of their host stars3,4. Only the recent discoveries of young planetary transiting systems allow initial constraints to be placed on evolutionary models5–7. With an estimated age of 20 million years, V1298 Tau is one of the youngest solar-type stars known to host transiting planets; it harbours a system composed of four planets, two Neptune-sized, one Saturn-sized and one Jupiter-sized8,9. Here we report a multi-instrument radial velocity campaign of V1298 Tau, which allowed us to determine the masses of two of the planets in the system. We find that the two outermost giant planets, V1298 Tau b and e (0.64 ± 0.19 and 1.16 ± 0.30 Jupiter masses, respectively), seem to contradict our knowledge of early-stages planetary evolution. According to models, they should reach their mass–radius combination only hundreds of millions of years after formation. This result suggests that giant planets can contract much more quickly than usually assumed

    High-performance fiber-reinforced concrete: a review

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