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19 April 2024 |
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Composition of the Galactic bulge | | Andrew McWilliam
; R. Michael Rich
; | | Date: |
27 Dec 2003 | | Subject: | astro-ph | | Abstract: | We present detailed abundance results for 9 Galactic bulge stars in Baade’s Window, based on HIRES (R=45,000--60,000) spectra taken with the Keck I telescope. The alpha elements show non-uniform enhancements relative to the Solar neighborhood trends: Mg and Si are enhanced in all our bulge stars by $sim$0.5--0.3 dex, showing a slight decrease with increasing [Fe/H]. Oxygen is enhanced in most bulge stars, similar to the Galactic halo, but the [O/Fe] ratios suddenly decline beginning at [Fe/H]=$-$0.5 dex, with a slope consistent with no oxygen production in the bulge for [Fe/H]$geq$$-$0.5 dex. The observed production of magnesium in the absence of oxygen synthesis appears to be inconsistent with current predictions for supernova nucleosynthesis yields; we suggest that this may be connected to the Wolf-Rayet phenomenon, which occurs in the pertinent metallicity range. The trend of [Ti/Fe] shows an enhancement relative to the solar neighborhood of $sim$0.3 dex, but declines somewhat by solar metallicity; thus, the Ti trend is less extreme than found by McWilliam & Rich (1994, MR94). For metal-poor bulge stars calcium is enhanced by $sim$0.3 dex, similar to the Galactic halo, but in our bulge stars with [Fe/H]$geq$$-$0.5, Ca show a slight deficiency relative to the solar neighborhood value, consistent with the findings of MR94; this may indicate a slightly top-heavy IMF as suggested by MR94 and McWilliam (1997). Aluminum is enhanced in all our Galactic bulge giant stars by $sim$0.25 dex; we argue that this is consistent with nucleosynthesis dominated by type II supernova events (SNII), implied by the Mg and Si enhancements. (Abridged) | | Source: | arXiv, astro-ph/0312628 | | Services: | Forum | Review | PDF | Favorites | |
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