Astron. Astrophys. 344, 317-321 (1999)

5. Conclusions

We have investigated the effect of the electron impact ionization on the filtration of the interstellar oxygen in the heliospheric interface. On the basis of the investigation we conclude:

1. Electron impact ionization acts on the interstellar oxygen penetrating in the heliosphere and leads to non-negligible additional filtration of the oxygen atoms in the region of the compressed and heated solar wind.

2. In our model, about 70% of interstellar oxygen penetrate in the heliosphere through the heliospheric interface. For the same solar and interstellar parameters only 47.5% of interstellar hydrogen penetrate in the heliosphere. Thus we conclude that the heliospheric relative abundance of OI to HI is larger than the interstellar abundance.

3. As it has been discussed in Sect. 3, the electron impact ionization leads to the increase of the number density of hot energetic neutrals (population 2) in the compressed solar wind (comparison of curves 1 and 2 in Fig. 2c). This is a consequence of the reverse charge-exchange reaction ( and could be important for the heliopause mapping in the oxygen ion resonance line recently proposed by Gruntman & Fahr (1998).

4. Only 30% of interstellar O atoms in the heliosphere are secondary atoms, while for hydrogen they are about 70%. These secondary interstellar atoms are created in the region between the BS and the TS by charge-exchange with the heated and stopped interstellar protons. The secondary atoms have a smaller velocity and a larger temperature compared with the primary atoms. As a consequence, in the heliosphere, interstellar oxygen atoms have a larger temperature and a smaller velocity than interstellar hydrogen atoms.

5. The comparison of the HST-GHRS spectroscopic data of Capella (Linsky et al., 1995) with heliospheric pick-up ion measurements shows a rather good agreement between data and theory. However, the accuracy of the filtration factor ratio derived from the experimental data is still too uncertain to allow a determination of the interstellar plasma density in an independent way.

© European Southern Observatory (ESO) 1999

Online publication: March 10, 1999
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