Abundances of Baade’s Window Giants from Keck HIRES Spectra. II. The Alpha and Light Odd Elements

By Jon P. Fulbright, A. McWilliam, R. Rich. 2006

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We report detailed abundances of O, Na, Mg, Al, Si, Ca, and Ti—elements produced by massive stars—for 27 red giants toward the Galactic bulge in Baade's window. These species are overabundant in the bulge relative to the disk, consistent with enhancement by Type II SN ejecta. [Mg/Fe] = +0.3 dex over the full range of [Fe/H], while O, Si, Ca, and Ti are elevated but follow more disklike trends. We propose that the decline in [O/Fe] is due to metallicity-dependent oxygen yields from massive stars, perhaps connected with the Wolf-Rayet phenomenon. The elements Si, Ca, and Ti, believed to be produced during explosive nucleosynthesis, possess identical trends with [Fe/H]. We attribute the decline of these elements to metallicity-dependent yields in Type II SNe. The trend of [Al/Fe] is found to vary strikingly with environment; the range from the Sgr dwarf to the bulge is 0.7 dex. The disjoint composition of the thick/thin disk and bulge stars is inconsistent with models in which the bulge formed from the thickening of the disk, while the elevated alpha elements are consistent with a rapid bulge formation timescale. The starkly smaller scatter of [⟨SiCaTi⟩/Fe] with [Fe/H] in the bulge compared with the halo is consistent with the expectation that the bulge should have efficiently mixed. The metal-poor bulge [⟨SiCaTi⟩/Fe] ratios are higher than ~80% of the halo; the bulge could not have formed from gas with the present-day halo composition.

Subfields: Astronomy and Astrophysics

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Citations in the corpus

COUNTING LOW-MASS STARS IN INTEGRATED LIGHT (2011, background): “3 dex and has an average of [Na/Fe]=0.2 (Fulbright et al. 2007).”
Chemical Similarities Between Galactic Bulge And Local Thick Disk Red Giant Stars (2008, methodology): “In contrast to previous works on the topic (Zoccali et al. 2006; Fulbright et al. 2007; Lecureur et al. 2007), we find that the two populations are indistinguishable in their abundance patterns for the elements considered (C, N and O) up to [Fe/H] = −0.2, i.e. to the metallicity range where the…”
Properties of stellar generations in globular clusters and relations with global parameters (2010, methodology): “To this purpose, we collected data for field stars from three different sources: Gratton et al. (2003a); Venn et al. (2004), and Fulbright et al. (2007).”
THE RADIAL VELOCITY EXPERIMENT (RAVE): SECOND DATA RELEASE (2008, result): “The results are consistent with those resulting from the analysis using the excitation temperature and equivalent widths of Fe I and Fe II lines to derive iron abundance, temperature and gravity (Fulbright et al. 2006, 2007).”
Stellar Proper Motions in the Galactic Bulge from Deep Hubble Space Telescope ACS WFC Photometry (2008, background): “A recent spec- troscopic comparisonwith halo objects shows themajority of bulge stars to be -enhanced compared to the halo; thus, themajority bulge stellar population cannot have formed from the halo (Fulbright et al. 2006, 2007).”
Chemical tagging with APOGEE: Discovery of a large population of N-rich stars in the inner Galaxy (2016, background): “When studied individually, α elements were found not to follow all exactly the same trend with metallicity (Fulbright et al. 2007) and, perhaps most importantly, to be slightly more enhanced in metal-rich bulge stars than in their thin and thick disk counterparts (Johnson et al. 2014).”
The metallicity distribution of bulge clump giants in Baade’s window (2011, methodology): “We further note that Fulbright et al. (2007) derive [Mg/Fe] = +0.02 for μLeo, 0.20 lower than what we found for this star (Lecureur et al. 2007).”
Alpha element abundances and gradients in the Milky Way bulge from FLAMES-GIRAFFE spectra of 650 K giants (2011, background): “…2010, and references therein) and that the formation of the bulge was fast as evidenced by the enhanced alpha elements in bulge stars (McWilliam & Rich 1994; Rich & Origlia 2005; Zoccali et al. 2006; Fulbright et al. 2006, 2007; Lecureur et al. 2007; Meléndez et al. 2008; Ryde et al. 2009, 2010).”
Insights on the Milky Way bulge formation from the correlations between kinematics and metallicity (2010, background): “On the other hand, from medium and high-resolution spectroscopic data enhancements of α elements have been observed (McWilliam & Rich 1994; Zoccali et al. 2006; Fulbright et al. 2007; Lecureur et al. 2007) suggesting a short formation time-scale.”
OUR MILKY WAY AS A PURE-DISK GALAXY—A CHALLENGE FOR GALAXY FORMATION (2010, background): “But those stars could have formed over a short period of time but long before the bar structure formed (Wyse 1999; Freeman 2008), their old age (Zoccali et al. 2003; Fulbright et al. 2007) is therefore not an argument against the internal secular evolu- tion model.”
The metal content of bulge field stars from FLAMES-GIRAFFE spectra - I. Stellar parameters and iron abundances (2008, background): “…bulge comes from the observedα-element enhancement (McWilliam & Rich 1994, 2003; Barbuy et al. 2006; Zoccali et al. 2004, 2006; Lecureur et al. 2007; Fulbright et al. 2007), once this is interpreted as a result of the interplay of the fast delivery of iron-poor nucleosynthesis products of massive…”
Chemical similarities between Galactic bulge and local thick disk red giants: O, Na, Mg, Al, Si, Ca, and Ti (2010, methodology): “…would have to be confirmed by a significantly larger bulge sample than we have access to here; adding the most metal-rich stars from the Lecureur et al. study would be worthwhile in this respect (as mentioned earlier, our bulge sample consists of the stars observed by Fulbright et al. 2006, 2007).”