相关论文: Oxygen in the Very Early Galaxy
We investigate statistical equilibrium of Cr in the atmospheres of late-type stars. The main goal is to ascertain the reason for a systematic abundance discrepancy between Cr I and Cr II lines, which is often encountered in spectroscopic…
A comprehensive model atom for Fe with more than 3000 energy levels is presented. As a test and first application of this model atom, Fe abundances are determined for the Sun and five stars with well determined stellar parameters and…
Context. Although oxygen is an important tracer of Galactic chemical evolution, measurements of its abundance in the atmospheres of the oldest Galactic stars are still scarce and rather imprecise. At the lowest end of the metallicity scale,…
The accurate O, Mg and Fe abundances derived in previous papers of this series from a homogenous reanalysis of high quality data for a large sample of stars are combined with stellar kinematics in order to discuss the history of star…
Context: The first stars produced the first heavy elements and set the stage for the formation of the first galaxies. Accurate chemical abundances of ultra metal-poor stars ([Fe/H]<-4) can be used to infer properties of the first stars, and…
We take a fresh look at the abundance of nitrogen in DLAs with oxygen abundances between 1/10 and 1/100 of solar. This is a metallicity regime poorly sampled in the local universe and where QSO absorbers may hold clues to both the…
We determined the silicon abundances of 253 metal-poor stars in the metallicity range $-4<\mathrm{[Fe/H]} <-1.5$, based on non-local thermodynamic equilibrium (NLTE) line formation calculations of neutral silicon and high-resolution spectra…
We present high-resolution UES spectra of the quasar PHL 957 obtained for studying the foreground Damped Ly-alpha galaxy at z=2.309. Measurements of absorption lines lead to accurate abundance determinations of Fe, S and N which complement…
We present 6.5-meter MMT and 3.5m APO spectrophotometry of 69 H II regions in 42 low-metallicity emission-line galaxies, selected from the Data Release 7 of the Sloan Digital Sky Survey to have mostly [O III]4959/Hbeta < 1 and [N…
Atmospheric parameters and chemical compositions for ten stars with metallicities in the region of -2.2< [Fe/H] <-0.6 were precisely determined using high resolution, high signal to noise, spectra. For each star the abundances, for 14 to 27…
We present a preliminary local thermodynamic equilibrium (LTE) abundance analysis of the template halo red giant HD122563 based on a realistic, three-dimensional (3D), time-dependent, hydrodynamical model atmosphere of the very metal-poor…
We spectroscopically analyzed a sample of 85 Sloan Digital Sky Survey compact, oxygen-dominated galaxies located at redshift $z\sim0.001-0.350$, selected because of their large equivalent width of [O III]$\lambda$5007 (larger than 200\AA).…
We present new MMT spectroscopic observations of four dwarf galaxies representative of a larger sample observed by the Sloan Digital Sky Survey (SDSS) and identified by Peeples et al. (2008) as low-mass, high oxygen abundance outliers from…
Ultraviolet nebular emission lines are important for understanding the time evolution and nucleosynthetic origins of their associated elements, but the underlying trends of their relative abundances are unclear. We present UV spectroscopy…
Models of star formation in the early universe depend on the details of accretion, fragmentation and radiative feedback. Different simulations predict different initial mass functions of the first stars, ranging from predominantly low mass…
For the first time, a direct NLTE analysis of carbon and nitrogen lines in the spectra of nine RR Lyrae stars was carried out. We have determined the abundances of these elements together with oxygen, and have shown that the nitrogen…
LTE abundances of light elements in extremely metal-poor (EMP) stars have been previously derived from high quality spectra. New derivations, free from the NLTE effects, will better constrain the models of the Galactic chemical evolution…
Due to their different nucleosynthetic origin, a stellar population produces oxygen (O) and iron (Fe) on different timescales and their relative abundance can deviate strongly from solar. Galaxy formation models should treat these elements…
Oxygen abundance measurements are important for understanding stellar structure and evolution. Measured in Cepheids, they further provide clues on the metallicity gradient and chemo-dynamical evolution in the Galaxy. However, most of the…
We study the formation of O I and OH spectral lines in three-dimensional hydrodynamic models of the solar photosphere. The line source function of the O I 777 nm triplet is allowed to depart from local thermodynamic equilibrium (LTE),…