7,402 research outputs found

    Cool dwarfs in wide multiple systems. Paper 6: A curious quintuple system of a compact Sun-like triple and a close pair of an M dwarf and a very cool white dwarf at a wide separation

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    The system WDS 16329+0315 is an old, nearby quintuple physical system in the thick Galactic disc formed by a close-resolved, triple primary of solar metallicity, namely HD 149162, and a very wide, common proper motion, secondary pair, formed by the mid-M dwarf G-17-23 and the white dwarf LSPM J1633+0311S. We present an exhaustive astrometric and photometric data compilation of the system, including Gaia DR2 parallaxes and proper motions, and the first analysis of the nature of the faintest component. LSPM J1633+0311S (HD 149162 C) is a very cool white dwarf with an effective temperature of only about 5500 K, near the coolest end of the grid of theoretical models.Comment: The Observatory, in press, to appear in December 201

    Rare top decay and CP violation in THDM

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    We discuss the formalism of two Higgs doublet model type III with CP violation from CP-even CP-odd mixing in the neutral Higgs bosons. The flavor changing interactions among neutral Higgs bosons and fermions are presented at tree level in this type of model. These assumptions allow the study rare top decays mediated by neutral Higgs bosons, particularly we are interested in tcl+lt\rightarrow c l^+l^-. For this process we estimated upper bounds of the branching ratios Br(tcτ+τ)\textrm{Br}(t\rightarrow c \tau^+\tau^-) of the order of 10910710^{-9}\sim 10^{-7} for a neutral Higgs boson mass of 125 GeV and tanβ=1\tan\beta=1, 1.5, 2, 2.5. For the case of tcτ+τt\rightarrow c \tau^+\tau^- the number of possible events is estimated from 1 to 10 events which could be observed in future experiments at LHC with a luminosity of 300 fb1\textrm{fb}^{-1} and 14 GeV for the energy of the center of mass. Also we estimate that the number of events for the process tcl+lt\rightarrow c l^+l^- in different scenarios is of order of 25002500.Comment: 8 pages, 5 figure

    The effect of magnetic activity saturation in chromospheric flux-flux relationships

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    We present a homogeneous study of chromospheric and coronal flux-flux relationships using a sample of 298 late-type dwarf active stars with spectral types F to M. The chromospheric lines were observed simultaneously in each star to avoid spread due to long term variability. Unlike other works, we subtract the basal chromospheric contribution in all the spectral lines studied. For the first time, we quantify the departure of dMe stars from the general relations. We show that dK and dKe stars also deviate from the general trend. Studying the flux-colour diagrams we demonstrate that the stars deviating from the general relations are those with saturated X-ray emission and that those stars also present saturation in the Hα\alpha line. Using several age spectral indicators, we show that they are younger stars than those following the general relationships. The non-universality of flux-flux relationships found in this work should be taken into account when converting between fluxes in different chromospheric activity indicators.Comment: Accepted for publication in the Monthly Notices of the Royal Astronomical Societ
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