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Peer-reviewedCC BYThe Astrophysical Journal

The LBT Y p Project. IV. A New Value of the Primordial Helium Abundance

  • Erik Aver1
  • Evan D. Skillman2
  • Richard W. Pogge3
  • Noah S. J. Rogers4
  • Miqaela K Weller3
  • Keith A. Olive2
  • Danielle A. Berg5
  • John J. Salzer6
  • John H Miller2
  • J. Eduardo Méndez-Delgado7
7 affiliations
  1. 1Gonzaga University
  2. 2University of Minnesota
  3. 3The Ohio State University
  4. 4Northwestern University
  5. 5The University of Texas at Austin
  6. 6Indiana University
  7. 7Universidad Nacional Autónoma de México
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Abstract

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 describe a number of updates to our methodology, including updated helium emissivities. Enabled by the large, high-quality dataset, we examine our sample targets for potential systematic errors, which could bias their results. We perform a standard 95% confidence level (CL) χ 2 cut and find that a significantly larger fraction (47/54 = 87%) of our sample qualifies than for previous datasets. We also screen for quality and reliability, flagging targets that may introduce significant systematic errors, producing a dataset of 41 targets. In a significant breakthrough for the field, that dataset includes 15 high signal-to-noise ratio (SNR) targets with low metallicity (O/H ≤ 4 × 10 −5 ). Due to this low-metallicity dataset, for the first time, a weighted average for determining the primordial helium abundance ( y p ) is well justified and produces a robust result. By weighted average of our 15 low-metallicity targets, we determine y p = 0.08146 ± 0.00058, with the corresponding mass fraction Y p = 0.2458 ± 0.0013. This result achieves an unprecedented precision of 0.5%, and it is in good agreement with the Big Bang nucleosynthesis (BBN) result, Y p = 0.2467 ± 0.0002, based on the Planck determination of the baryon density.

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Cite

BibTeXRIS
BibTeX
@article{aver2026project,
  title = {{The LBT Y p Project. IV. A New Value of the Primordial Helium Abundance}},
  author = {Erik Aver and Evan D. Skillman and Richard W. Pogge and Noah S. J. Rogers and Miqaela K Weller and Keith A. Olive and Danielle A. Berg and John J. Salzer and John H Miller and J. Eduardo Méndez-Delgado},
  journal = {The Astrophysical Journal},
  year = {2026},
  month = sep,
  doi = {10.3847/1538-4357/ae879b},
  url = {https://doi.org/10.3847/1538-4357/ae879b},
  note = {CC BY},
}
RIS
TY  - JOUR
TI  - The LBT Y p Project. IV. A New Value of the Primordial Helium Abundance
AU  - Erik Aver
AU  - Evan D. Skillman
AU  - Richard W. Pogge
AU  - Noah S. J. Rogers
AU  - Miqaela K Weller
AU  - Keith A. Olive
AU  - Danielle A. Berg
AU  - John J. Salzer
AU  - John H Miller
AU  - J. Eduardo Méndez-Delgado
PY  - 2026
DA  - 2026/09/09
JO  - The Astrophysical Journal
DO  - 10.3847/1538-4357/ae879b
UR  - https://doi.org/10.3847/1538-4357/ae879b
AB  - 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 describe a number of updates to our methodology, including updated helium emissivities. Enabled by the large, high-quality dataset, we examine our sample targets for potential systematic errors, which could bias their results. We perform a standard 95% confidence level (CL) χ 2 cut and find that a significantly larger fraction (47/54 = 87%) of our sample qualifies than for previous datasets. We also screen for quality and reliability, flagging targets that may introduce significant systematic errors, producing a dataset of 41 targets. In a significant breakthrough for the field, that dataset includes 15 high signal-to-noise ratio (SNR) targets with low metallicity (O/H ≤ 4 × 10 −5 ). Due to this low-metallicity dataset, for the first time, a weighted average for determining the primordial helium abundance ( y p ) is well justified and produces a robust result. By weighted average of our 15 low-metallicity targets, we determine y p = 0.08146 ± 0.00058, with the corresponding mass fraction Y p = 0.2458 ± 0.0013. This result achieves an unprecedented precision of 0.5%, and it is in good agreement with the Big Bang nucleosynthesis (BBN) result, Y p = 0.2467 ± 0.0002, based on the Planck determination of the baryon density.
SN  - 0004-637X
SN  - 1538-4357
ER  -