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

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2. Sagittarius dwarf galaxy: age and metallicity

The photometric metallicity estimates made for the SDG thus far depend heavily on the assumed age. The values for [Fe/H] range from -0.5 to -1.8 dex . According to Ibata et al. (1997) the mean age (10 - 12 Gyr) and metallicity ([Fe/H] = - 1.5) adopted is a trade-off, such that the age conveniently allows for the presence RR Lyrae and carbon stars. The age range is acceptable for the RR Lyrae stars, but it is inconsistent with the evolutionary calculations for the carbon stars mentioned in Sect. 1.

Preliminary results, based on HST WFPC2 data, reported by Mighell et al. (1998) yielded [Fe/H] [FORMULA] - 0.4 for a 4 and 6 Gyr population 1. The presence of an even younger population could not be established due to the small solid angle covered by the WFPC2.

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© European Southern Observatory (ESO) 1998

Online publication: September 14, 1998
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