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Astron. Astrophys. 338, 435-441 (1998)

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7. Summary

The results obtained from the analysis by Ng (1997) of the hypothesis that the ALRW91 C-stars are located at a SDG related distance have been improved.

[FORMULA] The metallicity of the ALRW91 C-stars is Z [FORMULA] 0.004.

[FORMULA] The age of the ALRW91 C-stars is [FORMULA]0.1 Gyr.

In this paper the average velocity and the velocity dispersion of the ALRW91 C-stars were taken into consideration. They added the conditions that the stars

o cannot be member of the SDG;

o are not a tidally stripped moving group;

o were not formed on the approach of the SDG towards the Galactic midplane;

[FORMULA] have to be formed during a recent crossing of the SDG through the Galactic plane at about 14.8 kpc behind the Galactic Bulge.

In addition, a comparison of the near-infrared photometry between the SDG & the ALRW91 C-stars indicated that they do not originate from the same star formation event: the SDG C-stars are older and metal-richer than the ALRW91 C-stars.

The condition that the SDG must have crossed the Galactic plane will remain a point of dispute until definite proper motions are obtained with the HST or GAIA (Global Astrometric Interferometer for Astrophysics).

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© European Southern Observatory (ESO) 1998

Online publication: September 14, 1998