相关论文: The primordial Helium-4 abundance determination: s…
We determine the primordial helium mass fraction Yp using 93 spectra of 86 low-metallicity extragalactic HII regions. This sample constitutes the largest and most homogeneous high-quality data sets in existence for the determination of Yp.…
We use spectroscopic observations of a sample of 82 HII regions in 76 blue compact galaxies to determine the primordial helium abundance Yp and the slope dY/dZ from the Y-O/H linear regression. To improve the accuracy of the dY/dZ…
We present a new determination of the primordial helium mass fraction Yp, based on 93 spectra of 86 low-metallicity extragalactic HII regions, and taking into account the latest developments concerning systematic effects. These include…
We have used recent observations of helium-4, nitrogen and oxygen from some four dozen, low metallicity, extra-galactic HII regions to define mean $N$ versus $O$, $^4He$ versus $N$ and $^4He$ versus $O$ relations which are extrapolated to…
Blue compact galaxies (BCG) are ideal objects in which to derive the primordial 4He abundance because they are chemically young and have not had a significant stellar He contribution. We discuss a self-consistent method which makes use of…
We have derived a primordial helium abundance of Yp = 0.2477 +- 0.0029, based on new atomic physics computations of the recombination coefficients of He I and of the collisional excitation of the H I Balmer lines together with observations…
We present high-quality spectroscopic observations of the two most-metal deficient blue compact galaxies known, I Zw 18 and SBS 0335-052 to determine the helium abundance. The underlying stellar absorption strongly influences the observed…
We include new data in an updated analysis of helium in low metallicity extragalactic HII regions with the goal of deriving the primordial abundance of He4 (Y_P). We show that the new observations of Izotov et al (ITL) are consistent with…
We present a new determination of the primordial helium abundance based on new, high-quality Large Binocular Telescope (LBT) observations of 54 metal-poor H II regions. These regions have been observed and analyzed uniformly. We also…
The primordial helium abundance Y_p is commonly inferred from abundance determinations in low-metallicity extragalactic HII-regions. Such determinations may be subject to systematic uncertainties that are investigated here. Particular…
Currently there are two significantly different observational determinations of the primordial helium abundance, and, if only statistical errors in He4 abundance determinations are considered, the discrepancies between the observational…
The precision measurement of the primordial helium abundance $Y_p$ is a powerful probe of the early Universe. The most common way to determine $Y_p$ is analyses of observations of metal-poor \HII regions found in blue compact dwarf…
The discordance between `low' and `high' primordial D/H measurements can be considerably reduced if the analysis of the H+D profiles accounts for the correlated velocity field of bulk motion. We have re-estimated the value of D/H at z=3.572…
A reanalysis is made for the helium abundance determination for the Izotov-Thuan (2004) spectroscopic sample of extragalactic H II regions. We find that the effect of underlying stellar absorption of the He I lines, which is more important…
Based on observations of HII regions and the new computations of the recombination coefficients of the He I lines by Porter et al. (2013) we obtain a primordial helium abundance by mass of $Y_P = 0.2446\pm0.0029$. We consider thirteen…
Within the standard models of particle physics and cosmology we have calculated the big-bang prediction for the primordial abundance of \he to a theoretical uncertainty of less than $0.1 \pct$ $(\delta Y_P < \pm 0.0002)$, improving the…
Observations of metal-poor extragalactic H II regions allow the determination of the primordial helium abundance, Y_p. The He I emissivities are the foundation of the model of the H II region's emission. Porter, Ferland, Storey, & Detisch…
We study the effect that the temperature structure has on the determination of the primordial helium abundance, Yp. We provide an equation linking T(OIII), the temperature derived from the [OIII] lines, and T(HeII), the temperature of the…
The primordial abundance of $^4$He plays a central role in big-bang nucleosynthesis (BBN) and in the cosmic microwave background (CMB). The LBT $Y_{\rm p}$ Project's new measurement of the primordial $^4$He mass fraction $Y_{\rm p} =0.2458…
We verified the validity of the empirical method to derive the 4He abundance used in our previous papers by applying it to CLOUDY (v13.01) models. Using newly published HeI emissivities, for which we present convenient fits as well as the…