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Title:
The Milky Way 3-Helium Abundance
Authors:
Bania, T. M.; Rood, R. T.; Balser, D. S.
Affiliation:
AA(Department of Astronomy, Institute for Astrophysical Research, Boston University), AB(Department of Astronomy, University of Virginia), AC(National Radio Astronomy Observatory)
Publication:
Space Science Reviews, Volume 130, Issue 1-4, pp. 53-62 (SSRv Homepage)
Publication Date:
06/2007
Origin:
SPRINGER
DOI:
10.1007/s11214-007-9144-z
Bibliographic Code:
2007SSRv..130...53B

Abstract

We are making precise determinations of the abundance of the light isotope of helium, 3He. The 3He abundance in Milky Way sources impacts stellar evolution, chemical evolution, and cosmology. The abundance of 3He is derived from measurements of the hyperfine transition of 3He+ which has a rest wavelength of 3.46 cm (8.665 GHz). As with all the light elements, the present interstellar 3He abundance results from a combination of Big Bang Nucleosynthesis (BBNS) and stellar nucleosynthesis. We are measuring the 3He abundance in Milky Way H ii regions and planetary nebulae (PNe). The source sample is currently comprised of 60 H ii regions and 12 PNe. H ii regions are examples of zero-age objects that are young relative to the age of the Galaxy. Therefore their abundances chronicle the results of billions of years of Galactic chemical evolution. PNe probe material that has been ejected from low-mass ( M≤ 2 M ȯ) to intermediate-mass ( M˜2 5 M ȯ) stars to be further processed by future stellar generations. Because the Milky Way ISM is optically thin at centimeter wavelengths, our source sample probes a larger volume of the Galactic disk than does any other light element tracer of Galactic chemical evolution. The sources in our sample possess a wide range of physical properties (including object type, size, temperature, excitation, etc.). The 3He abundances we derive have led to what has been called “The 3He Problem”.
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