Hot subdwarf stars in close-up view - IV. Helium abundances and the 3He isotopic anomaly of subdwarf B starsS. Geier, U. Heber, H. Edelmann, L. Morales-Rueda, D. Kilkenny, D. O’Donoghue, T. R. Marsh and C. CopperwheatA&A, 557 (2013) A122DOI: https://doi.org/10.1051/0004-6361/201322057
