A new method for determining the 3He/4He ratio in the local interstellar medium

Details A new method for determining the 3He/4He ratio in the local interstellar medium A new method for determining the 3He/4He ratio in the local interstellar medium

Jun 1993

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993a%26a...273..611l&link_type=abstract

Astronomy and Astrophysics, Vol. 273, p. 611 (1993)

Astronomy and Astrophysics

Astrophysics

3

Methods: Data Analysis, Interstellar Medium: Abundances, Galaxy: Evolution, Artificial Satellites, Space Probes

Scientific paper

We propose here an original method for estimating the 3He/4 Heratio in the local diffuse interstellar medium at a low cost from an observational point of view. The main idea is to measure the shift in radial velocity of the 4He λ537Å and λ584Å lines due to the presence of 3He in the red wing of these lines, and to compare the observed shift to the shifts obtained through numerical simulations for different 3He/4He ratios. We performed such simulations in order to reveal the efficiency of this method, using typical astrophysical conditions and instrumental parameters corresponding to the Lyman-FUSE mission. We find that this method should yield the 3He/4He ratio with a 1 σ uncertainty ˜50% at a spectral resolving power R=30 000 and a signal-to-noise ratio S/N=50. This method thus appears more adapted to a forehand estimation of the interstellar 3He/4He ratio than the standard profile fitting method, which should yield a 1 σ uncertainty of 10% at R=30 000 and S/N ≃ 290 (Hurwitz & Bowyer, t985). Finally, our method should be able to settle the evolutionary status of 3He if 3He has been significantly enhanced or depleted in the last 4.6 Gyr. Combined with the measurement of the deuterium abundance on the same line of sight (already programmed on HST), this might yield very important constraint on Big-Bang nucleosynthesis consistency.

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