A new approach to systematic uncertainties and self-consistency in helium abundance determinations

By E. Aver, K. Olive, E. Skillman. 2010

163 citations recorded by the source corpus.

Tests of big bang nucleosynthesis and early universe cosmology require precision measurements for helium abundance determinations. However, efforts to determine the primordial helium abundance via observations of metal poor H II regions have been limited by significant uncertainties (compared with the value inferred from BBN theory using the CMB determined value of the baryon density). This work builds upon previous work by providing an updated and extended program in evaluating these uncertainties. Procedural consistency is achieved by integrating the hydrogen based reddening correction with the helium based abundance calculation, i.e., all physical parameters are solved for simultaneously. We include new atomic data for helium recombination and collisional emission based upon recent work by Porter \etal and wavelength dependent corrections to underlying absorption are investigated. The set of physical parameters has been expanded here to include the effects of neutral hydrogen collisional emission. It is noted that Hγ and Hδ allow better isolation of the collisional effects from the reddening. Because of a degeneracy between the solutions for density and temperature, the precision of the helium abundance determinations is limited. Also, at lower temperatures (T 13,000 K) the neutral hydrogen fraction is poorly constrained resulting in a larger uncertainty in the helium abundances. Thus, the derived errors on the helium abundances for individual objects are larger than those typical of previous studies. Seven previously analyzed, ``high quality'' H II region spectra are used for a primordial helium abundance determination. The updated emissivities and neutral hydrogen correction generally raise the abundance. From a regression to zero metallicity, we find Yp as 0.2561 ± 0.0108, in broad agreement with the WMAP result. Alternatively, a simple average of the data yields Yp 0.2566 ± 0.0028. Tests with synthetic data show a potential for distinct improvement, via removal of underlying absorption, using higher resolution spectra. A small bias in the abundance determination can be reduced significantly and the calculated helium abundance error can be reduced by ~ 25%.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/be20781dde5b7f46f9afbf7c22898af0d5202532

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In Astronomy and Astrophysics

1. E. Aver
2. E. Skillman
3. Y. Izotov
4. T. Thuan
5. K. Olive
6. P. Serpico
7. G. Mangano
8. Usa

In Instrumentation

1. P. Serpico
2. G. Mangano
3. K. Olive
4. E. Skillman
5. E. Aver
6. T. Thuan
7. Y. Izotov
8. U. Virginia

Citations in the corpus

• The effects of He I λ10830 on helium abundance determinations (2015, methodology): “The neutral hydrogen fraction, ξ, is very poorly constrained for very low temperatures, due to its exponential temperature dependence (see AOS [39]).”
• A robust upper limit on Neff from BBN, circa 2011 (2011, methodology): “By now, there is some empirical evidence of this trend (positive derivative) even in the few high-quality objects analyzed in [7, 8].”
• CONSTRAINTS ON COSMOLOGY FROM THE COSMIC MICROWAVE BACKGROUND POWER SPECTRUM OF THE 2500 deg2 SPT-SZ SURVEY (2012, background): “Historically, these results have shown substantial variations between groups that greatly exceed the expected statistical variations; for a more complete discussion of these measurements, see e.g., Aver et al. (2010).”
• A MEASUREMENT OF THE DAMPING TAIL OF THE COSMIC MICROWAVE BACKGROUND POWER SPECTRUM WITH THE SOUTH POLE TELESCOPE (2011, background): “The primordial 4He abundance may also be inferred from observations of low-metallicity extragalactic HII regions (Izotov et al. 2007; Peimbert et al. 2007; Izotov & Thuan 2010; Aver et al. 2010, 2011).”
• Thermalisation of light sterile neutrinos in the early universe (2012, background): “Also, cosmological constraints coming from big bang nucleosynthesis (BBN) suggest that the relatively high 4He abundance can be interpreted in terms of additional radiation during the BBN epoch [24, 25].”
• STANDARD BIG BANG NUCLEOSYNTHESIS UP TO CNO WITH AN IMPROVED EXTENDED NUCLEAR NETWORK (2011, background): “The primordial 4He abundance Yp (mass fraction) is given by the extrapolation to zero metallicity but is affected by systematic uncertainties (Aver et al. 2010; Izotov & Thuan 2010) such as plasma temperature or stellar absorption.”
• New light species and the CMB (2013, background): “0108 [46], which are consistent with a larger rate of expansion.”
• A new determination of the primordial He abundance using the He i λ10830 Å emission line: cosmological implications (2014, methodology): “Most of the known systematic effects have generally been taken into account in the most recent work on the determination of the helium abundance(e.g. Izotov et al. 2007; Izotov & Thuan 2010; Peimbert et al. 2007; Aver et al. 2010, 2012, 2013).”