471 research outputs found

    HD 5388 b is a 69 M_Jup companion instead of a planet

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    We examined six exoplanet host stars with non-standard Hipparcos astrometric solution, which may be indicative of unrecognised orbital motion. Using Hipparcos intermediate astrometric data, we detected the astrometric orbit of HD 5388 at a significance level of 99.4 % (2.7 sigma). HD 5388 is a metal-deficient star and hosts a planet candidate with a minimum mass of 1.96 M_J discovered in 2010. We determined its orbit inclination to be i = 178.3 +0.4/-0.7 deg and the corresponding mass of its companion HD 5388 b to be M_2 = 69 +/- 20 M_J. The orbit is seen almost face-on and the companion mass lies at the upper end of the brown-dwarf mass range. A mass lower than 13 M_J was excluded at the 3-sigma level. The astrometric motions of the five other stars had been investigated by other authors revealing two planetary companions, one stellar companion, and two statistically insignificant orbits. We conclude that HD 5388 b is not a planet but most likely a brown-dwarf companion. In addition, we find that the inclinations of the stellar rotation axis and the companion's orbital axis differ significantly.Comment: 5 pages, 4 figures, Accepted for publication in Astronomy and Astrophysics Letter

    Early Developmental Processes and the Continuity of Risk for Underage Drinking and Problem Drinking

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    Developmental pathways to underage drinking emerge before the second decade of life. Many scientists, however, as well as the general public, continue to focus on proximal influences surrounding the initiation of drinking in adolescence, such as social, behavioral, and genetic variables related to availability and ease of acquisition of the drug, social reinforcement for its use, and individual differences in drug responses. In the past 20 years, a considerable body of evidence has accumulated on the early (often much earlier than the time of the first drink) predictors and pathways of youthful alcohol use and abuse. These early developmental influences involve numerous risk, vulnerability, promotive, and protective processes. Some of these factors are not related directly to alcohol use, whereas others involve learning and expectancies about later drug use that are shaped by social experience. The salience of these factors (identifiable in early childhood) for understanding the course and development of adult alcohol and other drug use disorders is evident from the large and growing body of findings on their ability to predict adult clinical outcomes. This review summarizes the evidence on early pathways toward and away from underage drinking, with a particular focus on the risk and protective factors and the mediators and moderators of risk for underage drinking that become evident during the preschool and early school years. It is guided by a developmental perspective on the aggregation of risk and protection and examines the contributions of biological, psychological, and social processes within the context of normal development.Implications of this evidence for policy, intervention, and future research are discussed.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/65125/1/UM 33 Zucker2008_EarlyDevelopmentalProc.Pediatrics_InPress_.pd

    Extrasolar planets in stellar multiple systems

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    Analyzing exoplanets detected by radial velocity or transit observations, we determine the multiplicity of exoplanet host stars in order to study the influence of a stellar companion on the properties of planet candidates. Matching the host stars of exoplanet candidates detected by radial velocity or transit observations with online multiplicity catalogs in addition to a literature search, 57 exoplanet host stars are identified having a stellar companion. The resulting multiplicity rate of at least 12 percent for exoplanet host stars is about four times smaller than the multiplicity of solar like stars in general. The mass and the number of planets in stellar multiple systems depend on the separation between their host star and its nearest stellar companion, e.g. the planetary mass decreases with an increasing stellar separation. We present an updated overview of exoplanet candidates in stellar multiple systems, including 15 new systems (compared to the latest summary from 2009).Comment: 11 pages, 4 figures, appendix with 6 tables, accepted for publication in A&

    A New Giant Stellar Structure in the Outer Halo of M31

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    The Sloan Digital Sky Survey has revealed an overdensity of luminous red giant stars ~ 3 degrees (40 projected kpc) to the northeast of M31, which we have called Andromeda NE. The line-of-sight distance to Andromeda NE is within approximately 50 kpc of M31; Andromeda NE is not a physically unrelated projection. Andromeda NE has a g-band absolute magnitude of ~ -11.6 and central surface brightness of ~ 29 mag/sq.arcsec, making it nearly two orders of magnitude more diffuse than any known Local Group dwarf galaxy at that luminosity. Based on its distance and morphology, Andromeda NE is likely undergoing tidal disruption. Andromeda NE's red giant branch color is unlike that of M31's present-day outer disk or the stellar stream reported by Ibata et al. (2001), arguing against a direct link between Andromeda NE and these structures. However, Andromeda NE has a red giant branch color similar to that of the G1 clump; it is possible that these structures are both material torn off of M31's disk in the distant past, or that these are both part of one ancient stellar stream.Comment: 11 pages, 3 figures; ApJ Letters accepted versio

    Permutability of proofs in intuitionistic sequent calculi

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    We prove a folklore theorem, that two derivations in a cut-free sequent calculus for intuitionistic propositional logic (based on Kleene's {\bf G3}) are inter-permutable (using a set of basic "permutation reduction rules'' derived from Kleene's work in 1952) iff they determine the same natural deduction. The basic rules form a confluent and weakly normalising rewriting system. We refer to Schwichtenberg's proof elsewhere that a modification of this system is strongly normalising.UniĂŁo Europeia (UE) - Programa ESPRIT BRA 7232 GENTZEN.Centro de MatemĂĄtica da Universidade do Minho (CMAT)

    Update on the Nature of Virgo Overdensity

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    We use the Eighth Data Release of Sloan Digital Sky Survey (SDSS DR8) catalog with its additional sky coverage of the southern Galactic hemisphere, to measure the extent and study the nature of the Virgo Overdensity (VOD; Juric et al. 2008). The data show that the VOD extends over no less than 2000 deg^2, with its true extent likely closer to 3000 deg^2. We test whether the VOD can be attributed to a tilt in the stellar halo ellipsoid with respect to the plane of the Galactic disk and find that the observed symmetry of the north-south Galactic hemisphere star counts excludes this possibility. We argue that the Virgo Overdensity, in spite of its wide area and cloud-like appearance, is still best explained by a minor merger. Its appearance and position is qualitatively similar to a near perigalacticon merger event and, assuming that the VOD and the Virgo Stellar Stream share the same progenitor, consistent with the VSS orbit determined by Casetti-Dinescu et al. (2009).Comment: 9 pages,6 figures; accepted for publication in A

    To B or not to B: a question of resolution?

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    A simple rule of thumb based on resolution is not adequate to identify the best treatment of atomic displacements in macromolecular structural models. The choice to use isotropic B factors, anisotropic B factors, TLS models or some combination of the three should be validated through statistical analysis of the model refinement

    Forming Different Planetary Systems

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    With the increasing number of detected exoplanet samples, the statistical properties of planetary systems have become much clearer. In this review, we summarize the major statistics that have been revealed mainly by radial velocity and transiting observations, and try to interpret them within the scope of the classical core-accretion scenario of planet formation, especially in the formation of different orbital architectures for planetary systems around main sequence stars. Based on the different possible formation routes for different planet systems, we tentatively classify them into three major catalogs: hot Jupiter systems, standard systems and distant giant planet systems. The standard system can be further categorized into three sub-types under different circumstances: solar-like systems, hot Super-Earth systems, sub-giant planet systems. We also review the planet detection and formation in binary systems as well as planets in star clusters.Comment: 27 pages, 2 figures, 1 table, published in "Research in Astron. Astrophysics." 2012, 12,108
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