The first stars forged the first metals inside their stellar cores and eventually ejected them to the primordial IGM medium through supernovae explosions. These metals significantly influence the next generation of star formation. Therefore, it is very important to understand how these metals chemically enriched the early universe. In this poster, we use two popular codes, ZEUS-MP and FLASH,...
We present here a three-dimesional hydrodynamical simulation for star formation. Our aim is to explore the effect of the metal-line cooling on the thermodynamics of the star-formation process. We explore the effect of changing the metallicty of the gas from $Z/Z_{\odot}=-4$ to $Z/Z_{\odot}=-2$. Furthermore, we explore the implications of using the observational abundance pattern of a set of...
The very metal-poor stars are important in the Milky Way, which record the heavy element abundances produced in the first generations of stars, thus can help us to understand the earliest nucleosynthesis events. Thanks to the large sky surveys like HK survey, Hamburg/ESO survey, SDSS, RAVE, SkyMapper, the number of very metal-poor stars especially the Extremely Metal-Poor stars (EMP,...
We perform a cosmological simulation with a comoving volume of 1 Mpc$^{3}$ to study the birthplaces of Population III stars, using the adaptive mesh refinement code Enzo. We investigate the distribution of host halo masses and its relationship to the Lyman-Werner background intensity. In our sample of 697 host halos, we find that 84% of them have masses below the Machecek et al. (2001)...
Modern cosmological simulations suggest that one massive Pop-III star might form into multi stars due to the fragmentations of the star-forming cloud. Most of these stars are likely to develop into binaries instead of single isolated stars. In the case of close binaries, the interaction between two stars frequently occurs. It leads to drive a significant mass-transfer even affect the fate of...
Population III (Pop III) binary systems are expected to play a role in the re-ionization. Merging binary black hole (BBH) also can be formed by evolution of such binary system. We calculate the evolution of Pop III binary systems using the MESA code to investigate 1) the effect on the production of ionizing photons and 2) close BBH systems coalescing within the Hubble time. We consider the...
We present a novel approach for categorical analysis of strongly carbon-enhanced metal-poor (CEMP) stars using medium-resolution (R~1,800) spectra. Analysis of cool (Teff ~ 4000 K) CEMP stars is largely inhibited by a strong depression of the underlying continuum (veiling) by extreme molecular bands, making normalization and fitting of metallic features such as Ca II H&K lines difficult....
Supernovae explosions of population III stars were the first enrichment mechanisms in the early universe, encoding chemical signatures in next-generation stars, where low-mass stars could have survived until now. These objects can reveal information of the cosmic chemical evolution and early formation stages of the Galaxy. Tominaga studied this developing models including Pop III SNe feedback...
Population III stars are known to form in a warm environment due to a lack of coolant in the early Universe. The warm nature leads to a high accretion rate and a formation of a massive primordial accretion disk. A massive disk is known to be gravitationally unstable. In previous zoom-in cosmological numerical simulation, a spiral structure emerges out of the disk. The dense region then...
We present evidence for triggered star formation following a supernova of a metal-free (Population III) star, providing a direct connection between a single Population III star and a subset of extremely metal-poor stars. We simulate the formation and ensuing radiative and supernova feedback of several Population III stars in a cosmological volume with the adaptive mesh refinement code, Enzo....
It is well known that magnesium is largely produced by massive stars which explode as core-collapse supernovae at the end of their evolutionary stage. We observed several magnesium-enhanced metal poor stars with the Gemini North 8m telescope and obtained high-resolution (R~42,000) spectroscopic data using the GRACES system. We measured the abundance ratios of alpha elements (e.g. Mg, Si) and...
Chemical abundance ratios of ultra metal-poor (UMP; [Fe/H] < -4.0) stars hold the key to understanding the nature of the first generation of stars born in the early Universe, as well as the nucleosynthesis processes associated with their evolution. UMP stars are believed to be true second generation stars and, despite their importance, only about two dozen have been discovered thus far. In an...
We have investigated explosive nucleosynthesis in core-collapse supernovae (SNe) of massive stars, based on two-dimensional hydrodynamic simulations of the SN explosion. Employing a simplified light-bulb scheme for neutrino transport and excising a central part of a proto-neutron star (PNS), we follow long-term evolution of the SN explosion over 1.0 second after the core bounce for 22 massive...
We present an analysis of the kinematic properties of the Galactic halo stars, using over 100,000 main sequence turnoff (MSTO) stars observed in Sloan Digital Sky Survey. After separating the MSTO stars into an inner-halo region (IHR) and outer-halo region (OHR), based on the spatial variation of their [C/Fe], we find that stars in the OHR show a clear retrograde motion of -49 km/s and a more...
Stars with enhanced n-capture elements are very important for our understanding on the characteristics of n-capture processes under environments with different metallicities. The odd isotopic fractions of barium could directly show the relative contributions from the s- and r-processes, even maybe from the i-process. In this talk, I will show some work on the odd isotopic fractions of barium...
The first stars in the Universe (Population III) are thought to be the
responsible for synthesizing the first heavy elements, thereby creating
the chemical conditions from which the second generation of stars has formed. One of the aims of
current investigations is to better constraint the Initial Mass Function
of Pop III stars from the observed abundance patterns of extremely
metal poor...
Ancient, metal-poor dwarf galaxies provide some of the best links to the earliest nucleosynthesis in the nearby Universe. Stellar abundances in dwarf galaxies can be used to estimate nucleosynthetic yields from supernovae, which can in turn be used to distinguish among different physical models of these supernovae. In particular, manganese is a sensitive probe of the density of the white dwarf...
APOGEE contains more than hundred thousands new giant stars. This enabled us to collected an unprecedented and homogeneous sample of giant stars with light-element abundance variations similar to observed in SG globular cluster stars. If they are really former members of dissolved globular clusters, stars in these groups should show some of the basic SG-like chemical patterns known for stars...
