The metallicity extremes of the Sagittarius dSph using SALT spectroscopy of PNe.pdf

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The metallicity extremes of the Sagittarius dSph using SALT spectroscopy of PNe.pdf

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The metallicity extremes of the Sagittarius dSph using SALT spectroscopy of PNe

a r X i v : 0 7 0 7 .4 2 8 8 v 2 [ a s t r o - p h ] 8 M a y 2 0 0 8 Mon. Not. R. Astron. Soc. 000, 1–14 (2008) Printed 8 May 2008 (MN LATEX style file v2.2) The metallicity extremes of the Sagittarius dSph: SALT spectroscopy of PNe? Alexei Y. Kniazev,1,2? Albert A. Zijlstra,3,1 Eva K. Grebel,4 Leonid S. Pilyugin,5 Simon Pustilnik,2 Petri Va?isa?nen,1 David Buckley,1 Yas Hashimoto,1 Nicola Loaring,1 Encarni Romero,1 Martin Still,1 Eric B. Burgh,6 Kenneth Nordsieck6 1South African Astronomical Observatory, PO Box 9, 7935, Cape Town, South Africa 2Special Astrophysical Observatory, Nizhnij Arkhyz, Karachai-Circassia, 369167, Russia 3University of Manchester, School of Physics Astronomy, PO Box 88, Manchester M60 1QD 4Astronomisches Rechen-Institut, Zentrum fu?r Astronomie Heidelberg, University of Heidelberg, Mo?nchhofstr. 12–14, D-69120 Heidelberg, Germany 5Main Astronomical Observatory of National Academy of Sciences of Ukraine, 27 Zabolotnogo str., 03680 Kiev, Ukraine 6Space Astronomy Laboratory, University of Wisconsin, Madison, WI 53706, USA Accepted 2007 July ??. Received 2007 June ??; in original form 20?? October ?? ABSTRACT In this work we present the first spectroscopic results obtained with the Southern African Large Telescope (SALT) telescope during its perfomance-verification phase. We find that the Sagittarius dwarf spheroidal galaxy (Sgr) Sgr contains a youngest stellar population with [O/H] ≈ ?0.2 and age t 1Gyr, 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, BoBn1, is an extraordinary object in that the neon abundance exceeds that of oxygen. The abundances of S, Ar and Cl in BoBn1 yield the original stellar metallicity, corresponding to 12+log(O/H) = 6.72±0.16 dex which is 1/11