scholarly journals HERBS I: Metallicity and alpha enhancement along the Galactic bulge minor axis

2019 ◽  
Vol 486 (3) ◽  
pp. 3586-3603 ◽  
Author(s):  
L Duong ◽  
M Asplund ◽  
D M Nataf ◽  
K C Freeman ◽  
M Ness ◽  
...  
Keyword(s):  
Milky Way ◽  
High Efficiency ◽  
Survey Design ◽  
Minor Axis ◽  
Signal To Noise ◽  
Origin And Evolution ◽  
Element Abundances ◽  
Red Giant ◽  
The Vertical Distribution ◽  
Metallicity Distribution

ABSTRACT To better understand the origin and evolution of the Milky Way bulge, we have conducted a survey of bulge red giant branch and clump stars using the High Efficiency and Resolution Multi-Element Spectrograph on the Anglo–Australian Telescope. We targeted ARGOS survey stars with predetermined bulge memberships, covering the full metallicity distribution function. The spectra have signal-to-noise ratios comparable to, and were analysed using the same methods as the GALAH survey. In this work, we present the survey design, stellar parameters, distribution of metallicity, and alpha-element abundances along the minor bulge axis at latitudes b = −10°, − 7.5°, and −5°. Our analysis of ARGOS stars indicates that the centroids of ARGOS metallicity components should be located ≈0.09 dex closer together. The vertical distribution of α-element abundances is consistent with the varying contributions of the different metallicity components. Closer to the plane, alpha abundance ratios are lower as the metal-rich population dominates. At higher latitudes, the alpha abundance ratios increase as the number of metal-poor stars increases. However, we find that the trend of alpha-enrichment with respect to metallicity is independent of latitude. Comparison of our results with those of GALAH DR2 revealed that for [Fe/H] ≈ −0.8, the bulge shares the same abundance trend as the high-α disc population. However, the metal-poor bulge population ([Fe/H] ≲ −0.8) show enhanced alpha abundance ratios compared to the disc/halo. These observations point to fairly rapid chemical evolution in the bulge, and that the metal-poor bulge population does not share the same similarity with the disc as the more metal-rich populations.

scholarly journals APOGEE Chemical Abundance Patterns of the Massive Milky Way Satellites

2021 ◽  
Vol 923 (2) ◽  
pp. 172
Author(s):  
Sten Hasselquist ◽  
Christian R. Hayes ◽  
Jianhui Lian ◽  
David H. Weinberg ◽  
Gail Zasowski ◽  
...  
Keyword(s):  
Star Formation ◽  
Chemical Evolution ◽  
Milky Way ◽  
Dwarf Galaxy ◽  
Magellanic Clouds ◽  
Chemical Abundance ◽  
Element Abundances ◽  
Abundance Patterns ◽  
Galaxy Environment ◽  
Red Giant

Abstract The SDSS-IV Apache Point Observatory Galactic Evolution Experiment (APOGEE) survey has obtained high-resolution spectra for thousands of red giant stars distributed among the massive satellite galaxies of the Milky Way (MW): the Large and Small Magellanic Clouds (LMC/SMC), the Sagittarius Dwarf Galaxy (Sgr), Fornax (Fnx), and the now fully disrupted Gaia Sausage/Enceladus (GSE) system. We present and analyze the APOGEE chemical abundance patterns of each galaxy to draw robust conclusions about their star formation histories, by quantifying the relative abundance trends of multiple elements (C, N, O, Mg, Al, Si, Ca, Fe, Ni, and Ce), as well as by fitting chemical evolution models to the [α/Fe]–[Fe/H] abundance plane for each galaxy. Results show that the chemical signatures of the starburst in the Magellanic Clouds (MCs) observed by Nidever et al. in the α-element abundances extend to C+N, Al, and Ni, with the major burst in the SMC occurring some 3–4 Gyr before the burst in the LMC. We find that Sgr and Fnx also exhibit chemical abundance patterns suggestive of secondary star formation epochs, but these events were weaker and earlier (∼5–7 Gyr ago) than those observed in the MCs. There is no chemical evidence of a second starburst in GSE, but this galaxy shows the strongest initial star formation as compared to the other four galaxies. All dwarf galaxies had greater relative contributions of AGB stars to their enrichment than the MW. Comparing and contrasting these chemical patterns highlight the importance of galaxy environment on its chemical evolution.

scholarly journals Chemical composition of stellar populations in ω Centauri

2009 ◽  
Vol 5 (S268) ◽  
pp. 183-184 ◽  
Author(s):  
A. F. Marino ◽  
G. Piotto ◽  
R. Gratton ◽  
A. P. Milone ◽  
M. Zoccali ◽  
...  
Keyword(s):  
Chemical Composition ◽  
Milky Way ◽  
Stellar Populations ◽  
Preliminary Results ◽  
Giant Stars ◽  
Red Giant Stars ◽  
Red Giant ◽  
Metallicity Distribution

AbstractWe derive abundances of Fe, Na, O, α and s-elements from GIRAFFE@VLT spectra for more than 200 red giant stars in the Milky Way satellite ω Centauri. Our preliminary results are that: (i) we confirm that ω Centauri exhibits large star-to-star metallicity variation (~1.4 dex); (ii) the metallicity distribution reveals the presence of at least five stellar populations with different [Fe/H]; (iii) a distinct Na-O anticorrelation is clearly observed for the metal-poor and metal-intermediate stellar populations while apparently the anticorrelation disappears for the most metal rich populations. Interestingly the Na level grows with iron.

Combining asteroseismology and spectroscopy for obtaining precise abundances: CoRoT-GES and K2-RAVE

2017 ◽  
Vol 13 (S334) ◽  
pp. 162-165
Author(s):  
M. Valentini ◽  
Keyword(s):  
Spectroscopic Analysis ◽  
Surface Gravity ◽  
Red Giants ◽  
Atmospheric Parameters ◽  
Signal To Noise ◽  
Element Abundances ◽  
Giant Stars ◽  
Precision And Accuracy ◽  
Red Giant

AbstractThe spectroscopic analysis of red giant stars is hampered by difficulties in determining the surface gravity, log g. The presence of degeneracies, few lines sensitive to log g, limited spectral coverage and bad signal-to-noise, can affect the precision and accuracy of log g and, as a consequence, the quality of the element abundances. We show how the adoption of the seismic surface gravity can improve the spectroscopic analysis of red giants. As examples, we adopted the seismic gravity in the analysis of spectra taken by two different surveys: GES (high resolution) and RAVE (intermediate resolution). The results of this technique were the lifting of the log g-Teff degeneracy and more accurate and precise atmospheric parameters and abundances.

scholarly journals The AMBRE Project: r-process elements in the Milky Way thin and thick discs

2018 ◽  
Vol 619 ◽  
pp. A143 ◽  
Author(s):  
G. Guiglion ◽  
P. de Laverny ◽  
A. Recio-Blanco ◽  
N. Prantzos
Keyword(s):  
Chemical Evolution ◽  
Milky Way ◽  
Element Abundances ◽  
Thick Disc ◽  
Thin Disc ◽  
Solar Metallicity ◽  
R Process ◽  
Process Elements ◽  
Process Element ◽  
The Eu

Context. The chemical evolution of neutron capture elements in the Milky Way disc is still a matter of debate. There is a lack of statistically significant catalogues of such element abundances, especially those of the r-process. Aims. We aim to understand the chemical evolution of r-process elements in Milky Way disc. We focus on three pure r-process elements Eu, Gd, and Dy. We also consider a pure s-process element, Ba, in order to disentangle the different nucleosynthesis processes. Methods. We take advantage of high-resolution FEROS, HARPS, and UVES spectra from the ESO archive in order to perform a homogeneous analysis on 6500 FGK Milky Way stars. The chemical analysis is performed thanks to the automatic optimization pipeline GAUGUIN. We present abundances of Ba (5057 stars), Eu (6268 stars), Gd (5431 stars), and Dy (5479 stars). Based on the [α/Fe] ratio determined previously by the AMBRE Project, we chemically characterize the thin and the thick discs, and a metal-rich α-rich population. Results. First, we find that the [Eu/Fe] ratio follows a continuous sequence from the thin disc to the thick disc as a function of the metallicity. Second, in thick disc stars, the [Eu/Ba] ratio is found to be constant, while the [Gd/Ba] and [Dy/Ba] ratios decrease as a function of the metallicity. These observations clearly indicate a different nucleosynthesis history in the thick disc between Eu and Gd–Dy. The [r/Fe] ratio in the thin disc is roughly around +0.1 dex at solar metallicity, which is not the case for Ba. We also find that the α-rich metal-rich stars are also enriched in r-process elements (like thick disc stars), but their [Ba/Fe] is very different from thick disc stars. Finally, we find that the [r/α] ratio tends to decrease with metallicity, indicating that supernovae of different properties probably contribute differently to the synthesis of r-process elements and α-elements. Conclusions. We provide average abundance trends for [Ba/Fe] and [Eu/Fe] with rather small dispersions, and for the first time for [Gd/Fe] and [Dy/Fe]. This data may help to constrain chemical evolution models of Milky Way r- and s-process elements and the yields of massive stars. We emphasize that including yields of neutron-star or black hole mergers is now crucial if we want to quantitatively compare observations to Galactic chemical evolution models.

scholarly journals GAIA: origin and evolution of the Milky Way

2000 ◽  
Author(s):  
Gerard F. Gilmore ◽  
Klaas S. de Boer ◽  
Fabio Favata ◽  
Erik Hoeg ◽  
Mario G. Lattanzi ◽  
...  
Keyword(s):  
Milky Way ◽  
Origin And Evolution

scholarly journals CHEMICAL CARTOGRAPHY WITH APOGEE: METALLICITY DISTRIBUTION FUNCTIONS AND THE CHEMICAL STRUCTURE OF THE MILKY WAY DISK

2015 ◽  
Vol 808 (2) ◽  
pp. 132 ◽  
Author(s):  
Michael R. Hayden ◽  
Jo Bovy ◽  
Jon A. Holtzman ◽  
David L. Nidever ◽  
Jonathan C. Bird ◽  
...  
Keyword(s):  
Chemical Structure ◽  
Milky Way ◽  
Distribution Functions ◽  
Metallicity Distribution

scholarly journals Effects of the selection function on metallicity trends in spectroscopic surveys of the Milky Way

2017 ◽  
Vol 606 ◽  
pp. A97 ◽  
Author(s):  
G. Nandakumar ◽  
M. Schultheis ◽  
M. Hayden ◽  
A. Rojas-Arriagada ◽  
G. Kordopatis ◽  
...  
Keyword(s):  
Stellar Population ◽  
Milky Way ◽  
Target Selection ◽  
Selection Function ◽  
Population Synthesis ◽  
Sample Distribution ◽  
Stellar Population Synthesis ◽  
Source Sample ◽  
Correction Terms ◽  
Metallicity Distribution

Context. Large spectroscopic Galactic surveys imply a selection function in the way they performed their target selection. Aims. We investigate here the effect of the selection function on the metallicity distribution function (MDF) and on the vertical metallicity gradient by studying similar lines of sight using four different spectroscopic surveys (APOGEE, LAMOST, RAVE, and Gaia-ESO), which have different targeting strategies and therefore different selection functions. Methods. We use common fields between the spectroscopic surveys of APOGEE, LAMOST, RAVE (ALR) and APOGEE, RAVE, Gaia-ESO (AGR) and use two stellar population synthesis models, GALAXIA and TRILEGAL, to create mock fields for each survey. We apply the selection function in the form of colour and magnitude cuts of the respective survey to the mock fields to replicate the observed source sample. We make a basic comparison between the models to check which best reproduces the observed sample distribution. We carry out a quantitative comparison between the synthetic MDF from the mock catalogues using both models to understand the effect of the selection function on the MDF and on the vertical metallicity gradient. Results. Using both models, we find a negligible effect of the selection function on the MDF for APOGEE, LAMOST, and RAVE. We find a negligible selection function effect on the vertical metallicity gradients as well, though GALAXIA and TRILEGAL have steeper and shallower slopes, respectively, than the observed gradient. After applying correction terms on the metallicities of RAVE and LAMOST with respect to our reference APOGEE sample, our observed vertical metallicity gradients between the four surveys are consistent within 1σ. We also find consistent gradient for the combined sample of all surveys in ALR and AGR. We estimated a mean vertical metallicity gradient of − 0.241 ± 0.028 dex kpc-1. There is a significant scatter in the estimated gradients in the literature, but our estimates are within their ranges. Conclusions. We have shown that there is a negligible selection function effect on the MDF and the vertical metallicity gradients for APOGEE, RAVE, and LAMOST using two stellar population synthesis models. Therefore, it is indeed possible to combine common fields of different surveys in studies using MDF and metallicity gradients provided their metallicities are brought to the same scale.

scholarly journals A Kiloparsec-scale Molecular Wave in the Inner Galaxy: Feather of the Milky Way?

2021 ◽  
Vol 921 (2) ◽  
pp. L42
Author(s):  
V. S. Veena ◽  
P. Schilke ◽  
Á. Sánchez-Monge ◽  
M. C. Sormani ◽  
R. S. Klessen ◽  
...  
Keyword(s):  
Molecular Structure ◽  
Aspect Ratio ◽  
Milky Way ◽  
Spiral Galaxies ◽  
Galactic Center ◽  
Velocity Data ◽  
Sinusoidal Wave ◽  
Angular Extent ◽  
The Vertical Distribution ◽  
Spiral Arm

Abstract We report the discovery of a velocity coherent, kiloparsec-scale molecular structure toward the Galactic center region with an angular extent of 30° and an aspect ratio of 60:1. The kinematic distance of the CO structure ranges between 4.4 and 6.5 kpc. Analysis of the velocity data and comparison with the existing spiral arm models support that a major portion of this structure is either a subbranch of the Norma arm or an interarm giant molecular filament, likely to be a kiloparsec-scale feather (or spur) of the Milky Way, similar to those observed in nearby spiral galaxies. The filamentary cloud is at least 2.0 kpc in extent, considering the uncertainties in the kinematic distances, and it could be as long as 4 kpc. The vertical distribution of this highly elongated structure reveals a pattern similar to that of a sinusoidal wave. The exact mechanisms responsible for the origin of such a kiloparsec-scale filament and its wavy morphology remains unclear. The distinct wave-like shape and its peculiar orientation makes this cloud, named as the Gangotri wave, one of the largest and most intriguing structures identified in the Milky Way.

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