The Research On Detecting The First Generation Of Stars In The Galaxy

Abstract The first generations of stars(FGS) , which were formed from gas completely free of carbon and heavy elements, are unevolved and the oldest stars. No FGS has been found in our Galaxy. Stars with metallicities significantly below [Fe/H]<-2.5were exceedingly rare. Owing to a recent survey undertaken by Beers, Preston and Shectman (hereafter BPS), the number of known extremely metal-poor stars in the Galaxy has substantially increased. At present, the lowest metallicity star ever found [Fe/H]-4. 1. And the number of stars discovered with-4< [Fe/H] <-3 is above 100. The kinematics of these stars is similar to that of other halo stars. But we haven抰 found FGS, even no stars with metallicity [Fe/H]<-6 has been found. In order to explain the above phenomena of observation, Many models have been posed by the astronomers. In the paper, we summarize these models. Under the condition of no environment pollution.it is determined by the initial mass function (IMF) that if we can find FGS at last because IMF, which describes the frequency distribution of the mass of stellar when they formed can determine the characteristic of the stellar system and its evolution. There is few evidences to testify if IMF have a special or cut-off mass on the observation, the results from theory is that the shape of IMF is smooth at the low mass and steep at the high mass. Galaxy is composed of Galactic bulge, plate and halo. The metallicity of the Global cluster and field stars in the Galactic halo is very low, so the epoch when they formed is very early. they are the most location for us to detect FGS. In this paper we analyze the elemental factors to determine its chemical evolution on the theory ,and summarize the abundance distribution of elements in the halo stars according to their forming mechanism. We discuss the characteristic of the early Galactic chemical evolution through two inhomogeneous chemical evolution models contrapo sing the scatter of heavy elements. In the last section of this paper, we calculate and discuss the probability to detect FGS using the chemical evolution model of Galactic halo posed by Tsujimoto et al (TSY99) under the assumption that the first generation of star has Miller-Scab form of initial mass function .In this model, we assume that the star-forming process is confined to separate clouds which is initially composed of metal-free population III (pop III) stars and gas that has yet to form stars .Subsequent stars are born from each Type II Supernova remnant (SNR), the abundance pattern of each star is set by the heavy elements ejected from the SN explosion and those elements iii 慖 / \IA~TER ~ YHr~nz already present in the interstellar gas .When SNRS can no longer sweep up enough gas to form shells, The process will terminate. The parameter of model is confined by the observational data of the Galactic halo stars. The result suggests that the probability of identifying essentially metal-free stars in the local halo is around6. 14x1O~?. 14x1O~, provided that the star formation in the halo is confined to individual gas clouds with a mass oflOsM0~1O?M~. In addition, through the calculation we find that the stellar metallicity does not correspond to a unique age but that...