12,098 research outputs found
Neutrinos and the synthesis of heavy elements: the role of gravity
The synthesis of heavy elements in the Universe presents several challenges.
From one side the astrophysical site is still undetermined and on other hand
the input from nuclear physics requires the knowledge of properties of exotic
nuclei, some of them perhaps accessible in ion beam facilities. Black hole
accretion disks have been proposed as possible r-process sites. Analogously to
Supernovae these objects emit huge amounts of neutrinos. We discuss the
neutrino emission from black hole accretion disks. In particular we show the
influence that the black hole strong gravitational field has on changing the
electron fraction relevant to the synthesis of elements.Comment: 5 pages, 5 figures, Invited talk at the 15th International Symposium
on Capture Gamma-Ray Spectroscopy and Related Topics (CGS15), to appear in
EPJ Web of Conference
Neutrino Scattering in Heterogeneous Supernova Plasmas
Neutrinos in core collapse supernovae are likely trapped by neutrino-nucleus
elastic scattering. Using molecular dynamics simulations, we calculate neutrino
mean free paths and ion-ion correlation functions for heterogeneous plasmas.
Mean free paths are systematically shorter in plasmas containing a mixture of
ions compared to a plasma composed of a single ion species. This is because
neutrinos can scatter from concentration fluctuations. The dynamical response
function of a heterogeneous plasma is found to have an extra peak at low
energies describing the diffusion of concentration fluctuations. Our exact
molecular dynamics results for the static structure factor reduce to the Debye
Huckel approximation, but only in the limit of very low momentum transfers.Comment: 11 pages, 13 figure
The Gaia Ultra-Cool Dwarf Sample -- II : Structure at the end of the main sequence
© 2019 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society.We identify and investigate known late M, L, and T dwarfs in the Gaia second data release. This sample is being used as a training set in the Gaia data processing chain of the ultracool dwarfs work package. We find 695 objects in the optical spectral range M8–T6 with accurate Gaia coordinates, proper motions, and parallaxes which we combine with published spectral types and photometry from large area optical and infrared sky surveys. We find that 100 objects are in 47 multiple systems, of which 27 systems are published and 20 are new. These will be useful benchmark systems and we discuss the requirements to produce a complete catalogue of multiple systems with an ultracool dwarf component. We examine the magnitudes in the Gaia passbands and find that the G BP magnitudes are unreliable and should not be used for these objects. We examine progressively redder colour–magnitude diagrams and see a notable increase in the main-sequence scatter and a bivariate main sequence for old and young objects. We provide an absolute magnitude – spectral subtype calibration for G and G RP passbands along with linear fits over the range M8–L8 for other passbands.Peer reviewedFinal Published versio
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