45 research outputs found
Dynamics of neutrino-driven winds: inclusion of accurate weak interaction rates in strong magnetic fields
Solving Newtonian steady-state wind equations with accurate weak interaction
rates and magnetic fields (MFs) of young neutron stars considered, we study the
dynamics and nucleosynthesis of neutrino-driven winds (NDWs) from proto neutron
stars (PNSs). For a typical 1.4 M PNS model, we find the
nucleosynthesis products are closely related to the luminosity of neutrinos and
anti-neutrinos. The lower the luminosity is, the larger effect to the NDWs
caused by weak interactions and MFs is. At a high anti-neutrino luminosity of
typically erg s, neutrinos and anti-neutrinos dominate
the processes in a NDW and the MFs hardly change the wind's properties. While
at a low anti-neutrino luminosity of erg s at the late stage
of a NDW, the mass of product and nucleosynthesis are changed significantly in
the strong MFs, they are less important than those in the early stage when the
anti-neutrino luminosity is high. Therefore for the most models considered for
the NDWs from PNSs, based on our calculations the influences of MFs and the net
weak interactions on the nucleosynthesis is not significant.Comment: 8 pages, 3 figures, accepted for publication in RA
Effect of Electron Screening on the Collapsing Process of Core-Collapse Supernovae
By using an average heavy nuclei model, the effects of the electron screening
on electron capture (EC) in core-collapse supernovae are investigated. A
one-dimension code based on the Ws15M_{\sun} progenitor model is utilized to
test the effects of electron screening during the collapsing process. The
results show that, at high densities, the effects of EC on electron capture
becomes significant. During the collapsing stage, the EC rate is decreased, the
collapse timescale is prolonged and the leakage of the neutrino energy is
increased. These effects lead to an appreciable decrease in the initial energy
of the bounce shock wave. The effects of electron screeening in the other
progenitor models are also discussed.Comment: 5 pages, 4 figures, MNRAS in pres
The LAMOST Survey of Background Quasars in the Vicinity of the Andromeda and Triangulum Galaxies -- II. Results from the Commissioning Observations and the Pilot Surveys
We present new quasars discovered in the vicinity of the Andromeda and
Triangulum galaxies with the LAMOST during the 2010 and 2011 observational
seasons. Quasar candidates are selected based on the available SDSS, KPNO 4 m
telescope, XSTPS optical, and WISE near infrared photometric data. We present
509 new quasars discovered in a stripe of ~135 sq. deg from M31 to M33 along
the Giant Stellar Stream in the 2011 pilot survey datasets, and also 17 new
quasars discovered in an area of ~100 sq. deg that covers the central region
and the southeastern halo of M31 in the 2010 commissioning datasets. These 526
new quasars have i magnitudes ranging from 15.5 to 20.0, redshifts from 0.1 to
3.2. They represent a significant increase of the number of identified quasars
in the vicinity of M31 and M33. There are now 26, 62 and 139 known quasars in
this region of the sky with i magnitudes brighter than 17.0, 17.5 and 18.0
respectively, of which 5, 20 and 75 are newly-discovered. These bright quasars
provide an invaluable collection with which to probe the kinematics and
chemistry of the ISM/IGM in the Local Group of galaxies. A total of 93 quasars
are now known with locations within 2.5 deg of M31, of which 73 are newly
discovered. Tens of quasars are now known to be located behind the Giant
Stellar Stream, and hundreds behind the extended halo and its associated
substructures of M31. The much enlarged sample of known quasars in the vicinity
of M31 and M33 can potentially be utilized to construct a perfect astrometric
reference frame to measure the minute PMs of M31 and M33, along with the PMs of
substructures associated with the Local Group of galaxies. Those PMs are some
of the most fundamental properties of the Local Group.Comment: 26 pages, 6 figures, AJ accepte
Chemical Evolution of Mn in Three Dwarf Spheroidal Galaxies
Based on an improved model, more reasonable nucleosynthesis and explosion rate of SNeIa and CCSNe, we studied Mn evolution for three local dwarf spheroidal galaxies (dSphs), considering the detailed SNe yield and explosion rates for different types of progenitors. The results can explain the main observation of Mn abundance for tens stars in those dSphs, and give some constraints to the nucleosynthesis and explosion ratio of different types of supernovae and Star Formation Rates (SFR) in those dSphs
A new estimation of manganese distribution for local dwarf spheroidal galaxies
The distribution of abundance for iron-peak elements in dwarf spheroidal galaxies (dSphs) is important for galaxy evolution and supernova (SN) nucleosynthesis. Nowadays, manganese (Mn) is one of the most observed iron-peak elements in local dSphs. Studies of its distributions allow us to derive and understand the evolution history of these dSphs. We improve a phenomenological model by a two-curve model including a new initial condition, that includes detailed calculations of SN explosion rates and yields. We compare the results with the observed Mn distribution data for three dSphs: Fornax, Sculpture and Sextans. We find that the model can describe the observed Fe and Mn distributions well simultaneously for the three dSphs. The results also indicate that the initial conditions should be determined by the low metalli city samples in the beginning time of the galaxies and the previous assumption of metellicity-dependant Mn yield of SNIa is not needed when a wide mass range of core-collapse SNe is included. Our method is applicable to the chemical evolution of other iron-peak elements in dSphs and can be modified to provide more detailed processes for the evolution of dSphs