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We develop a method to compute synthetic kilonova light curves that combine numerical relativity simulations of neutron star mergers and the SNEC radiation–hydrodynamics code. We describe our implementation of initial and boundary conditions, r-process heating, and opacities for kilonova simulations. We validate our approach by carefully checking that energy conservation is satisfied and by comparing the SNEC results with those of two semi-analytic light-curve models. We apply our code to the calculation of colour light curves for three binaries having different mass ratios (equal and unequal mass) and different merger outcome (short-lived and long-lived remnants). We study the sensitivity of our results to hydrodynamic effects, nuclear physics uncertainties in the heating rates, and duration of the merger simulations. We find that hydrodynamics effects are typically negligible and that homologous expansion is a good approximation in most cases. However, pressure forces can amplify the impact of uncertainties in the radioactive heating rates. We also study the impact of shocks possibly launched into the outflows by a relativistic jet. None of our models match AT2017gfo, the kilonova in GW170817. This points to possible deficiencies in our merger simulations and kilonova models that neglect non-LTE effects and possible additional energy injection from the merger remnant and to the need to go beyond the assumption of spherical symmetry adopted in this work. [ABSTRACT FROM AUTHOR]

We investigate r -process nucleosynthesis and kilonova emission resulting from binary neutron star (BNS) mergers based on a three-dimensional (3D) general-relativistic magnetohydrodynamic (GRMHD) simulation of a hypermassive neutron star (HMNS) remnant. The simulation includes a microphysical finite-temperature equation of state (EOS) and neutrino emission and absorption effects via a leakage scheme. We track the thermodynamic properties of the ejecta using Lagrangian tracer particles and determine its composition using the nuclear reaction network SkyNet. We investigate the impact of neutrinos on the nucleosynthetic yields by varying the neutrino luminosities during post-processing. The ejecta show a broad distribution with respect to their electron fraction Ye , peaking between ∼0.25–0.4 depending on the neutrino luminosity employed. We find that the resulting r -process abundance patterns differ from solar, with no significant production of material beyond the second r -process peak when using luminosities recorded by the tracer particles. We also map the HMNS outflows to the radiation hydrodynamics code SNEC and predict the evolution of the bolometric luminosity as well as broadband light curves of the kilonova. The bolometric light curve peaks on the timescale of a day and the brightest emission is seen in the infrared bands. This is the first direct calculation of the r -process yields and kilonova signal expected from HMNS winds based on 3D GRMHD simulations. For longer-lived remnants, these winds may be the dominant ejecta component producing the kilonova emission. [ABSTRACT FROM AUTHOR]

ABSTRACT Based on Beijing-Arizona-Taiwan-Connecticut (BATC) and Sloan Digital Sky Survey (SDSS) photometric data, we adopt the spectral energy distribution (SED) fitting method to evaluate the metallicity distribution for ∼40 000 main-sequence stars in the Galaxy. According to the derived photometric metallicities of these sample stars, we find that the metallicity distribution shifts from metal-rich to metal-poor with the increase of distance from the Galactic Centre. The mean metallicity is about −1.5 ± 0.2 dex in the outer halo and −1.3 ± 0.1 dex in the inner halo and smoothly decreases from −0.4 to −0.8 in the interval 0 < r≤ 5 kpc. A fluctuation in mean metallicity with Galactic longitude can be found in the interval 4 < r≤ 8 kpc. There is a vertical abundance gradient d[Fe/H]/d z∼−0.21 ± 0.05 dex kpc−1 for the thin disc ( z≤ 2 kpc). At a distance 2 < z≤ 5 kpc, where thick-disc stars dominate, the gradient is about −0.16 ± 0.06 dex kpc−1; this can be interpreted as a mixture of stellar populations with different mean metallicities at all z levels. The vertical metallicity gradient is −0.05 ± 0.04 dex kpc−1 for the halo ( z > 5 kpc), so there is little or no metallicity gradient in the halo. [ABSTRACT FROM AUTHOR]