1,752 research outputs found

    Time-scales of close-in exoplanet radio emission variability

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    We investigate the variability of exoplanetary radio emission using stellar magnetic maps and 3D field extrapolation techniques. We use a sample of hot Jupiter hosting stars, focusing on the HD 179949, HD 189733 and tau Boo systems. Our results indicate two time-scales over which radio emission variability may occur at magnetised hot Jupiters. The first is the synodic period of the star-planet system. The origin of variability on this time-scale is the relative motion between the planet and the interplanetary plasma that is co-rotating with the host star. The second time-scale is the length of the magnetic cycle. Variability on this time-scale is caused by evolution of the stellar field. At these systems, the magnitude of planetary radio emission is anticorrelated with the angular separation between the subplanetary point and the nearest magnetic pole. For the special case of tau Boo b, whose orbital period is tidally locked to the rotation period of its host star, variability only occurs on the time-scale of the magnetic cycle. The lack of radio variability on the synodic period at tau Boo b is not predicted by previous radio emission models, which do not account for the co-rotation of the interplanetary plasma at small distances from the star.Comment: 10 pages, 7 figures, 2 tables, accepted in MNRA

    On the environment surrounding close-in exoplanets

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    Exoplanets in extremely close-in orbits are immersed in a local interplanetary medium (i.e., the stellar wind) much denser than the local conditions encountered around the solar system planets. The environment surrounding these exoplanets also differs in terms of dynamics (slower stellar winds, but higher Keplerian velocities) and ambient magnetic fields (likely higher for host stars more active than the Sun). Here, we quantitatively investigate the nature of the interplanetary media surrounding the hot Jupiters HD46375b, HD73256b, HD102195b, HD130322b, HD179949b. We simulate the three-dimensional winds of their host stars, in which we directly incorporate their observed surface magnetic fields. With that, we derive mass-loss rates (1.9 to 8.0 ×10−13M⊙\times 10^{-13} M_{\odot}/yr) and the wind properties at the position of the hot-Jupiters' orbits (temperature, velocity, magnetic field intensity and pressure). We show that these exoplanets' orbits are super-magnetosonic, indicating that bow shocks are formed surrounding these planets. Assuming planetary magnetic fields similar to Jupiter's, we estimate planetary magnetospheric sizes of 4.1 to 5.6 planetary radii. We also derive the exoplanetary radio emission released in the dissipation of the stellar wind energy. We find radio fluxes ranging from 0.02 to 0.13 mJy, which are challenging to be observed with present-day technology, but could be detectable with future higher sensitivity arrays (e.g., SKA). Radio emission from systems having closer hot-Jupiters, such as from tau Boo b or HD189733b, or from nearby planetary systems orbiting young stars, are likely to have higher radio fluxes, presenting better prospects for detecting exoplanetary radio emission.Comment: 15 pages, 5 figures, accepted to MNRA

    Unravelling Selection Shifts Among Foot-and-Mouth Disease Virus (FMDV) Serotypes

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    FMDV virus has been increasingly recognised as the most economically severe animal virus with a remarkable degree of antigenic diversity. Using an integrative evolutionary and computational approach we have compelling evidence for heterogeneity in the selection forces shaping the evolution of the seven different FMDV serotypes. Our results show that positive Darwinian selection has governed the evolution of the major antigenic regions of serotypes A, Asia1, O, SAT1 and SAT2, but not C or SAT3. Co-evolution between sites from antigenic regions under positive selection pinpoints their functional communication to generate immune-escape mutants while maintaining their ability to recognise the host-cell receptors. Neural network and functional divergence analyses strongly point to selection shifts between the different serotypes. Our results suggest that, unlike African FMDV serotypes, serotypes with wide geographical distribution have accumulated compensatory mutations as a strategy to ameliorate the effect of slightly deleterious mutations fixed by genetic drift. This strategy may have provided the virus by a flexibility to generate immune-escape mutants and yet recognise host-cell receptors. African serotypes presented no evidence for compensatory mutations. Our results support heterogeneous selective constraints affecting the different serotypes. This points to the possible accelerated rates of evolution diverging serotypes sharing geographical locations as to ameliorate the competition for the host

    Image method for the derivation of point sources in elastostatic problems with plane interfaces

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    An image method algorithm is presented for the derivation of point sources of elastostatics in multilayered media assuming the infinite space point source is known. Specific cases were worked out and shown to coincide with well known solutions in the literature

    Vector image method for the derivation of elastostatic solutions for point sources in a plane layered medium. Part 1: Derivation and simple examples

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    An image method algorithm is presented for the derivation of elastostatic solutions for point sources in bonded halfspaces assuming the infinite space point source is known. Specific cases were worked out and shown to coincide with well known solutions in the literature

    Magnetic field, differential rotation and activity of the hot-Jupiter hosting star HD 179949

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    HD 179949 is an F8V star, orbited by a giant planet at ~8 R* every 3.092514 days. The system was reported to undergo episodes of stellar activity enhancement modulated by the orbital period, interpreted as caused by Star-Planet Interactions (SPIs). One possible cause of SPIs is the large-scale magnetic field of the host star in which the close-in giant planet orbits. In this paper we present spectropolarimetric observations of HD 179949 during two observing campaigns (2009 September and 2007 June). We detect a weak large-scale magnetic field of a few Gauss at the surface of the star. The field configuration is mainly poloidal at both observing epochs. The star is found to rotate differentially, with a surface rotation shear of dOmega=0.216\pm0.061 rad/d, corresponding to equatorial and polar rotation periods of 7.62\pm0.07 and 10.3\pm0.8 d respectively. The coronal field estimated by extrapolating the surface maps resembles a dipole tilted at ~70 degrees. We also find that the chromospheric activity of HD 179949 is mainly modulated by the rotation of the star, with two clear maxima per rotation period as expected from a highly tilted magnetosphere. In September 2009, we find that the activity of HD 179949 shows hints of low amplitude fluctuations with a period close to the beat period of the system.Comment: Accepted for publication in Monthly Notices of The Royal Astronomical Societ

    Searching for Star-Planet interactions within the magnetosphere of HD 189733

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    HD 189733 is a K2 dwarf, orbited by a giant planet at 8.8 stellar radii. In order to study magnetospheric interactions between the star and the planet, we explore the large-scale magnetic field and activity of the host star. We collected spectra using the ESPaDOnS and the NARVAL spectropolarimeters, installed at the 3.6-m Canada-France-Hawaii telescope and the 2-m Telescope Bernard Lyot at Pic du Midi, during two monitoring campaigns (June 2007 and July 2008). HD 189733 has a mainly toroidal surface magnetic field, having a strength that reaches up to 40 G. The star is differentially rotating, with latitudinal angular velocity shear of domega = 0.146 +- 0.049 rad/d, corresponding to equatorial and polar periods of 11.94 +- 0.16 d and 16.53 +- 2.43 d respectively. The study of the stellar activity shows that it is modulated mainly by the stellar rotation (rather than by the orbital period or the beat period between the stellar rotation and the orbital periods). We report no clear evidence of magnetospheric interactions between the star and the planet. We also extrapolated the field in the stellar corona and calculated the planetary radio emission expected for HD 189733b given the reconstructed field topology. The radio flux we predict in the framework of this model is time variable and potentially detectable with LOFAR

    Genome Mutational and Transcriptional Hotspots Are Traps for Duplicated Genes and Sources of Adaptations

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    [EN] Gene duplication generates new genetic material, which has been shown to lead to major innovations in unicellular and multicellular organisms. A whole-genome duplication occurred in the ancestor of Saccharomyces yeast species but 92% of duplicates returned to single-copy genes shortly after duplication. The persisting duplicated genes in Saccharomyces led to the origin of major metabolic innovations, which have been the source of the unique biotechnological capabilities in the Baker's yeast Saccharomyces cerevisiae. What factors have determined the fate of duplicated genes remains unknown. Here, we report the first demonstration that the local genome mutation and transcription rates determine the fate of duplicates. We show, for the first time, a preferential location of duplicated genes in the mutational and transcriptional hotspots of S. cerevisiae genome. The mechanism of duplication matters, with whole-genome duplicates exhibiting different preservation trends compared to small-scale duplicates. Genome mutational and transcriptional hotspots are rich in duplicates with large repetitive promoter elements. Saccharomyces cerevisiae shows more tolerance to deleterious mutations in duplicates with repetitive promoter elements, which in turn exhibit higher transcriptional plasticity against environmental perturbations. Our data demonstrate that the genome traps duplicates through the accelerated regulatory and functional divergence of their gene copies providing a source of novel adaptations in yeast.This study was supported by a grant (reference: FEDER-BFU2015-66073-P) from the Spanish Ministerio de Economia y Competitividad-FEDER and a grant (reference: ACOMP/2015/026) from the local government Conselleria de Educacion Investigacion, Cultura y Deporte, Generalitat Valenciana to M.A.F. 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