Chemical abundances in the galactic bulge: evidence for a fast enrichment (original) (raw)
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Abundances in the Galactic bulge: results from planetary nebulae and giant stars
Astronomy & Astrophysics, 2008
Context. Our understanding of the chemical evolution (CE) of the Galactic bulge requires the determination of abundances in large samples of giant stars and planetary nebulae (PNe). Studies based on high resolution spectroscopy of giant stars in several fields of the Galactic bulge obtained with very large telescopes have allowed important progress. Aims. We discuss PNe abundances in the Galactic bulge and compare these results with those presented in the literature for giant stars. Methods. We present the largest, high-quality data-set available for PNe in the direction of the Galactic bulge (inner-disk/bulge). For comparison purposes, we also consider a sample of PNe in the Large Magellanic Cloud (LMC). We derive the element abundances in a consistent way for all the PNe studied. By comparing the abundances for the bulge, inner-disk, and LMC, we identify elements that have not been modified during the evolution of the PN progenitor and can be used to trace the bulge chemical enrichment history. We then compare the PN abundances with abundances of bulge field giant. Results. At the metallicity of the bulge, we find that the abundances of O and Ne are close to the values for the interstellar medium at the time of the PN progenitor formation, and hence these elements can be used as tracers of the bulge CE, in the same way as S and Ar, which are not expected to be affected by nucleosynthetic processes during the evolution of the PN progenitors. The PN oxygen abundance distribution is shifted to lower values by 0.3 dex with respect to the distribution given by giants. A similar shift appears to occur for Ne and S. We discuss possible reasons for this PNe-giant discrepancy and conclude that this is probably due to systematic errors in the abundance derivations in either giants or PNe (or both). We issue an important warning concerning the use of absolute abundances in CE studies.
Chemical evolution of the Galactic bulge
The Metal-Rich Universe, 2008
Adopting a single-zone framework, with accretion of primordial gas on a free-fall timescale, the chemical evolution of the Galactic bulge is calculated, assuming (i) a corresponding rapid timescale for star formation, and (ii) an initial mass function biased towards massive stars. We emphasise here the uncertainties associated with the underlying physics (specifically, stellar nucleosynthesis) and how those uncertainties are manifest in the predicted abundance ratio patterns in the resulting present-day Galactic bulge stellar populations. † In contrast to that of the halo, which despite its trace baryonic contribution to the Milky Way, has had at least ten times the number of models published to explain its origin.
Monthly Notices of the Royal Astronomical Society, 2023
Due to its proximity, the stellar populations of the Galactic bulge (GB) can be resolved and can be studied in detail. This allows tracing the bulge metallicity distribution function (MDF) for different spatial regions within the bulge, which may give us clues about the bulge formation and evolution scenarios. In this work, we developed a chemical evolution model (CEM), taking into account the mass distribution in the bulge and disc, to derive the radial dependence of this timescale in the Galaxy. Since the infall rate depends on that time scale in the CEM, the results of the model were used to test a scenario where the bulge is formed inside-out. The obtained results for the [ /Fe] vs. [Fe/H] relationship, the MDF and the [Fe/H] radial gradient in the bulge have been compared to available data in the literature. The model is able to reproduce most of the observational data: the spread in the relation [ /Fe] vs. [Fe/H], the MDF shape in different regions of the bulge, the [Fe/H] radial gradient inside it and the age-metallicity relation, as well as the [ /Fe] evolution with age. The results of the model point to a scenario where the bulk of the bulge stars pre-existed the boxy/peanut X-shape bar formation. As a result, the classical origin of the GB is not ruled out and this scenario may be invoked to explain the chemical properties of the Galactic bulge.
2013
This work began with my journey into graduate school in the Fall of 2008. Through the past five years I have grown immensely as both a scientist, and a person. I entered this field hesitantly curious, and am emerging hungry for knowledge through collaboration and my own critical analysis and reasoning. I have become a creative dreamer and found a sense of beauty in the way science can so simply explain aspects of our uniquely complex cosmos. I am truly left in awe and wonderment. And I get to experience this every day as an astrophysicist. That's right, I am a scientist.
Abundances in the Galactic bulge
Physica Scripta, 2008
The metallicity distribution and abundance ratios of the Galactic bulge are reviewed. Issues raised by recent work of different groups, in particular the high metallicity end, the overabundance of α-elements in the bulge relative to the thick disc and the measurement of giants versus dwarfs, are discussed. Abundances in the old moderately metal-poor bulge globular clusters are described.
Light and heavy elements in the galactic bulge
Arxiv preprint astro-ph/9810125, 1998
In the context of an inside-out model for the formation of our Galaxy we present results for the chemical evolution of the Galactic bulge by assuming that this central region evolved even faster than the Galactic halo. This assumption is required in order to reproduce the observed metallicity distribution of bulge stars as obtained by .
Oxygen, sodium, magnesium, and aluminium as tracers of the galactic bulge formation
Astronomy & Astrophysics, 2007
This paper investigates the peculiar behaviour of the light even (alpha-elements) and odd atomic number elements in red giants in the galactic bulge, both in terms of the chemical evolution of the bulge, and in terms of possible deep-mixing mechanisms in these evolved stars. Using UVES on VLT, we measure the abundances of the four light elements O, Na, Mg and Al in 13 red clump and 40 red giant branch stars in four fields spanning the bulge from b=-3 to -12\deg. We show that the resulting abundance patterns point towards a chemical enrichment dominated by massive stars at all metallicities. O, Mg and Al ratios with respect to iron are overabundant with respect to both galactic disks (thin and thick) for [Fe/H]$>-0.5$. A formation timescale for the galactic bulge shorter than for both the thin and thick disks is therefore inferred. Using Mg as a proxy for metallicity (instead of Fe) we further show that: (i) the bulge stars [O/Mg] ratio follows and extend to higher metallicities the decreasing trend of [O/Mg] found in the galactic disks. (ii) the [Na/Mg] ratio trend with increasing [Mg/H] is found to increase in three distinct sequences in the thin disk, the thick disk and the bulge. The bulge trend is well represented by the predicted metallicity-dependent yields of massive stars, whereas the galactic disks have too high Na/Mg ratios at low metallicities, pointing to an additional source of Na from AGB stars. (iii) Contrary to Na, there appears to be no systematic difference in the [Al/Mg] ratio between bulge and disk stars, and the theoretical yields by massive stars agree with the observed ratios, leaving no space for AGB contribution to Al.
Chemical abundances of 11 bulge stars from high-resolution, near-IR spectra
Astronomy and Astrophysics, 2010
Context. It is debated whether the Milky Way bulge has characteristics more similar to those of a classical bulge than those of a pseudobulge. Detailed abundance studies of bulge stars are important when investigating the origin, history, and classification of the bulge. These studies provide constraints on the star-formation history, initial mass function, and differences between stellar populations. Not many similar studies have been completed because of the large distance and high variable visual extinction along the line-of-sight towards the bulge. Therefore, near-IR investigations can provide superior results. Aims. To investigate the origin of the bulge and study its chemical abundances determined from near-IR spectra for bulge giants that have already been investigated with optical spectra. The optical spectra also provide the stellar parameters that are very important to the present study. In particular, the important CNO elements are determined more accurately in the near-IR. Oxygen and other α elements are important for investigating the star-formation history. The C and N abundances are important for determining the evolutionary stage of the giants and the origin of C in the bulge. Methods. High-resolution, near-infrared spectra in the H band were recorded using the CRIRES spectrometer mounted on the Very Large Telescope. The CNO abundances are determined from the numerous molecular lines in the wavelength range observed. Abundances of the α elements Si, S, and Ti are also determined from the near-IR spectra. Results. The abundance ratios [O/Fe], [Si/Fe], and [S/Fe] are enhanced to metallicities of at least [Fe/H] = −0.3, after which they decline. This suggests that the Milky Way bulge experienced a rapid and early burst of star formation similar to that of a classical bulge. However, a similarity between the bulge trend and the trend of the local thick disk seems to be present. This similarity suggests that the bulge could have had a pseudobulge origin. The C and N abundances suggest that our giants are first-ascent red-giants or clump stars, and that the measured oxygen abundances are those with which the stars were born. Our [C/Fe] trend does not show any increase with [Fe/H], which is expected if W-R stars contributed substantially to the C abundances. No "cosmic scatter" can be traced around our observed abundance trends: the measured scatter is expected, given the observational uncertainties.