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18 February 2025
 
  » arxiv » astro-ph/0112064

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On the primordial helium content: CMB and stellar constraints
G. Bono ; A. Balbi ; S. Cassisi ; N. Vittorio ; R. Buonanno ;
Date 4 Dec 2001
Journal Astrophys.J. 568 (2002) 463-469
Subject astro-ph
AffiliationObservatory of Rome), A. Balbi (Tor Vergata University, Rome), S. Cassisi (Observatory of Teramo), N. Vittorio (Tor Vergata University, Rome), R. Buonanno (Observatory of Rome
AbstractWe present the results of a joint investigation aimed at constraining the primordial He content ($Y_P$) on the basis of both the Cosmic Microwave Background (CMB) anisotropy and two stellar observables, namely the tip of the Red Giant Branch (TRGB) and the luminosity of the Zero Age Horizontal Branch (ZAHB). Current baryon density estimates based on CMB measurements cover a wide range values $0.009la Omega_bh^2 la 0.045$, that according to Big Bang Nucleosynthesis (BBN) models would imply $0.24la Y_P la 0.26$. We constructed several sets of evolutionary tracks and HB models by adopting $Y_P=0.26$ and several metal contents. The comparison between theory and observations suggests that ZAHB magnitudes based on He-enhanced models are 1.5$sigma$ brighter than the empirical ones. The same outcome applies for the TRGB bolometric magnitudes. This finding somewhat supports a $Y_P$ abundance close to the canonical 0.23-0.24 value. More quantitative constraints on this parameter are hampered by the fact that the CMB pattern shows a sizable dependence on both $Y_P$ and the baryon density only at small angular scales, i.e. at high l in the power spectrum ($lga 100$). However, this region of the power spectrum could be still affected by deceptive systematic uncertainties. Finally, we suggest to use the {em UV-upturn} to estimate the He content on Gpc scales. In fact, we find that a strong increase in $Y_P$ causes in metal-poor, hot HB structures a decrease in the UV emission.
Source arXiv, astro-ph/0112064
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