Towards a Measurement of the Primordial Helium Isotope Ratio*

The Astrophysical Journal 2026 Open access

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Authors: Ryan Cooke, James W. Johnson, P. Noterdaeme, Max Pettini, Louise Welsh, Aldric Wong, Céline Péroux
DOI: 10.3847/1538-4357/ae66f8
Cited by: 1
References: 125

Abstract

Abstract We report the discovery of two metastable neutral helium (He I *) absorbers in the Milky Way, and use the upgraded CRyogenic InfraRed Echelle Spectrograph (or CRIRES) on the Very Large Telescope to determine the helium isotope ratio, 3 He/ 4 He, along these sight lines. We have also obtained deeper observations of a third sight line to report a ≲4% precision measure of 3 He/ 4 He in the Orion Nebula. These data have allowed us to place a 2 σ limit on the time variability of He I * absorption in the Orion Nebula, d log 10 [ N ( He I ∗ ) / cm − 2 ] / d t ≤ 7.2 × 1 0 − 4 dex yr − 1 (

Fields of Study & Subjects

Astrophysics and Star Formation Studies Astro and Planetary Science Stellar planetary and galactic studies

Publication details

Journal / source
The Astrophysical Journal
Publisher
American Astronomical Society
Volume
1003
Issue
2
Pages
225–225
Publication date
28 May 2026
Language
EN