Journal Article

The metallicity extremes of the Sagittarius dSph: SALT spectroscopy of PNe*

Alexei Y. Kniazev, Albert A. Zijlstra, Eva K. Grebel, Leonid S. Pilyugin, Simon Pustilnik, Petri Väisänen, David Buckley, Yas Hashimoto, Nicola Loaring, Encarni Romero, Martin Still, Eric B. Burgh and Kenneth Nordsieck

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 388, issue 4, pages 1667-1678
Published in print August 2008 | ISSN: 0035-8711
Published online August 2008 | e-ISSN: 1365-2966 | DOI: http://dx.doi.org/10.1111/j.1365-2966.2008.13435.x
The metallicity extremes of the Sagittarius dSph: SALT spectroscopy of PNe*

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In this work we present the first spectroscopic results obtained with the Southern African Large Telescope (SALT) during its performance-verification phase. We find that the Sagittarius dwarf spheroidal galaxy (Sgr) contains a youngest stellar population with [O/H]≈−0.2 and age t > 1 Gyr, and an oldest population with [O/H] =−2.0. The values are based on spectra of two planetary nebulae (PNe), using empirical abundance determinations. We calculated abundances for O, N, Ne, Ar, S, Cl, Fe, C and He. We confirm the high abundances of PN StWr 2-21 with 12 + log(O/H) = 8.57 ± 0.02 dex. The other PN studied, BoBn 1, is an extraordinary object in that the neon abundance exceeds that of oxygen. The abundances of S, Ar and Cl in BoBn 1 yield the original stellar metallicity, corresponding to 12 + log(O/H) = 6.72 ± 0.16 dex which is 1/110 of the solar value. The actual [O/H] is much higher: third dredge-up enriched the material by a factor of ∼12 in oxygen, ∼240 in nitrogen and ∼70 in neon. Neon as well as nitrogen and oxygen content may have been produced in the intershell of low-mass asymptotic giant branch (AGB) stars. Well defined broad WR lines are present in the spectrum of StWr 2-21 and absent in the spectrum of BoBn 1. This puts the fraction of [WR]-type central PNe stars to 67 per cent for dSph galaxies.

Keywords: stars: abundances; stars: mass-loss; planetary nebulae: general; galaxies: individual: Sagittarius dwarf spheroidal

Journal Article.  8638 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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