- ID:
- ivo://CDS.VizieR/J/A+A/513/A35
- Title:
- Abundances of Galactic red giants
- Short Name:
- J/A+A/513/A35
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The formation and evolution of the Galactic bulge and its relationship with the other Galactic populations is still poorly understood. To establish the chemical differences and similarities between the bulge and other stellar populations, we performed an elemental abundance analysis of alpha- (O, Mg, Si, Ca, and Ti) and Z-odd (Na and Al) elements of red giant stars in the bulge as well as of local thin disk, thick disk and halo giants. We use high-resolution optical spectra of 25 bulge giants in Baade's window and 55 comparison giants (4 halo, 29 thin disk and 22 thick disk giants) in the solar neighborhood. All stars have similar stellar parameters but cover a broad range in metallicity (-1.5<[Fe/H]<+0.5). A standard 1D local thermodynamic equilibrium analysis using both Kurucz and MARCS models yielded the abundances of O, Na, Mg, Al, Si, Ca, Ti and Fe. Our homogeneous and differential analysis of the Galactic stellar populations ensured that systematic errors were minimized.
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Search Results
- ID:
- ivo://CDS.VizieR/J/A+A/480/79
- Title:
- Abundances of giants in five Galactic clusters
- Short Name:
- J/A+A/480/79
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- To constrain the formation and chemical evolution of the Galactic disk, we surveyed open clusters of different ages, metal contents, and distances form the Galactic centre. We employed FLAMES on VLT-UT2 to collect UVES spectra of five to ten giant stars in each of the selected clusters, and used them to derive the iron abundance and the detailed chemical composition. Equivalent widths were measured and abundance analysis was performed using the MOOG code and Kurucz model atmospheres on all stars accepted as cluster member on the basis of their radial velocity. We derived the atmospheric parameters and the abundance of Fe for NGC 2324 and NGC 2477 (average [Fe/H]=-0.17 with rms 0.05dex, and +0.07 with rms 0.03dex, respectively), two clusters never analyzed using high resolution spectroscopy. We also derived the abundances of Mg, Al, Ca, Si, Ti, Cr, Ni, and Ba for these two clusters and for NGC 2660, NGC 3960, and Berkeley 32, whose atmospheric parameters and metallicities were measured in a previous paper. We determined the reddening values for the five clusters, based on the spectroscopically determined temperatures, literature photometry, and a colour-temperature relation. All clusters show solar-scaled abundances for alpha- and Fe-peak elements, while [Na/Fe] appears slightly enhances and and [Ba/Fe] significantly enhanced. Our findings were compared to thin-disk stars and other open clusters, and no significant deviation from the standard behavior was found.
- ID:
- ivo://CDS.VizieR/J/A+A/488/943
- Title:
- Abundances of giants in four Galactic clusters
- Short Name:
- J/A+A/488/943
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- To constrain the formation and chemical evolution of the Galactic disk, we surveyed open clusters of different ages, metal contents, and distances form the Galactic centre. We employed FLAMES on VLT-UT2 to collect UVES spectra of bright giant stars in each of the selected clusters, and used them to derive the iron abundance and the detailed chemical composition. Equivalent widths were measured and abundance analysis was performed using the MOOG code and Kurucz model atmospheres. We derived the abundance of Fe for Mg, Al, Ca, Si, Ti, Cr, Ni, and Ba. We employed direct line profile fitting to derive non-LTE Na abundances. We found [Fe/H]=-0.30, -0.31, +0.13, -0.33 for Be 20, Be 29, Cr 261, and Melotte 66, respectively (with rms values of 0.02 to 0.05dex). Alpha- and Fe-peak elements have solar ratios, Ba is enhanced, and Na has solar ratios, suggesting that treatment of non-LTE is very important. We confirm the presence of a metallicity gradient in the inner disk, and a flattening in the outer part.
- ID:
- ivo://CDS.VizieR/J/A+A/554/A81
- Title:
- Abundances of 16 giants in M75
- Short Name:
- J/A+A/554/A81
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- M75 is a relatively young Globular Cluster (GC) found at 15kpc from the Galactic centre at the transition region between the inner and outer Milky Way halos. Our aims are to perform a comprehensive abundance study of a variety of chemical elements in this GC such as to investigate its chemical enrichment history in terms of early star formation, and to search for any multiple populations. We have obtained high resolution spectroscopy with the MIKE instrument at the Magellan telescope for 16 red giant stars. Their membership within the GC is confirmed from radial velocity measurements. Our chemical abundance analysis is performed via equivalent width measurements and spectral synthesis, assuming local thermodynamic equilibrium (LTE). We present the first comprehensive abundance study of M75 to date. The cluster is metal-rich ([Fe/H]=-1.16+/-0.02dex, [alpha/Fe]=+0.30+/-0.02dex), and shows a marginal spread in [Fe/H] of 0.07dex, typical of most GCs of similar luminosity. A moderately extended O-Na anticorrelation is clearly visible, likely showing three generations of stars, formed on a short timescale. Additionally the two most Na-rich stars are also Ba-enhanced by 0.4 and 0.6dex, respectively, indicative of pollution by lower mass (M~4-5M_{sun}_) Asymptotic Giant Branch (AGB) stars. The overall n-capture element pattern is compatible with predominant r-process enrichment, which is rarely the case in GCs of such a high metallicity.
- ID:
- ivo://CDS.VizieR/J/ApJ/732/108
- Title:
- Abundances of 92 giants in Plaut's window
- Short Name:
- J/ApJ/732/108
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present Fe, Si, and Ca abundances for 61 giants in Plaut's window (l=-1{deg}, b=-8.5{deg}) and Fe abundances for an additional 31 giants in a second, nearby field (l=0{deg}, b=-8{deg}) derived from high-resolution (R~25000) spectra obtained with the Blanco 4m telescope and Hydra multifiber spectrograph. The median metallicity of red giant branch (RGB) stars in the Plaut's field is ~0.4dex lower than those in Baade's window, and confirms the presence of an iron abundance gradient along the bulge minor axis. The full metallicity range of our (biased) RGB sample spans -1.5<[Fe/H]<+0.3, which is similar to that found in other bulge fields. We also derive a photometric metallicity distribution function for RGB stars in the (l=-1{deg}, b=-8.5{deg}) field and find very good agreement with the spectroscopic metallicity distribution. The radial velocity (RV) and dispersion data for the bulge RGB stars are in agreement with previous results of the Bulge Radial Velocity Assay survey, and we find evidence for a decreasing velocity dispersion with increasing [Fe/H]. The [{alpha}/Fe] enhancement in Plaut field stars is nearly identical to that observed in Baade's window, and suggests that an [{alpha}/Fe] gradient does not exist between b=-4{deg} and -8{deg}. Additionally, a subset of our sample (23 stars) appears to be foreground red clump stars that are very metal rich, exhibit small metallicity and RV dispersions, and are enhanced in {alpha} elements. While these stars likely belong to the Galactic inner disk population, they exhibit [{alpha}/Fe] ratios that are enhanced above the thin and thick disk.
- ID:
- ivo://CDS.VizieR/J/MNRAS/433/1892
- Title:
- Abundances of 848 giants of {omega} Cen
- Short Name:
- J/MNRAS/433/1892
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the effective temperatures, surface gravities and abundances of iron, carbon and barium of 848 giant branch stars, of which 557 also have well-defined nitrogen abundances, of the globular cluster {omega} Centauri. This work used photometric sources and lower resolution spectra for this abundance analysis. Spectral indices were used to estimate the oxygen abundance of the stars, leading to a determination of whether a particular star was oxygen rich or oxygen poor. The 557-star subset was analysed in the context of evolutionary groups, with four broad groups identified. These groups suggest that there were at least four main periods of star formation in the cluster. The exact order of these star formation events is not yet understood. These results compare well with those found at higher resolution and show the value of more extensive lower resolution spectral surveys. They also highlight the need for large samples of stars when working with a complex object like {omega} Cen.
- ID:
- ivo://CDS.VizieR/J/A+A/493/913
- Title:
- Abundances of 9 HB stars in NGC 6352
- Short Name:
- J/A+A/493/913
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Metal-rich globular clusters provide important tracers of the formation of our Galaxy. Moreover, and not less important, they are very important calibrators for the derivation of properties of extra-galactic metal-rich stellar populations. Nonetheless, only a few of the metal-rich globular clusters in the Milky Way have been studied using high-resolution stellar spectra to derive elemental abundances. Additionally, Rosenberg et al. identified a small group of metal-rich globular clusters that appeared to be about 2 billion years younger than the bulk of the Milky Way globular clusters. However, it is unclear if like is compared with like in this dataset as we do not know the enhancement of alpha-elements in the clusters and the amount of alpha-elements is well known to influence the derivation of ages for globular clusters. We present a study of elemental abundances for alpha and iron-peak elements for nine HB stars in the metal-rich globular cluster NGC 6352. The elemental abundances are based on high-resolution, high signal-to-noise spectra obtained with the UVES spectrograph on VLT. The elemental abundances have been derived using standard LTE calculations and stellar parameters have been derived from the spectra themselves by requiring ionizational as well as excitational equilibrium. We find that NGC 6352 has [Fe/H]=-0.55, is enhanced in the alpha-elements to about +0.2dex for Ca, Si, and Ti relative to Fe. For the iron-peak elements we find solar values. Based on the spectroscopically derived stellar parameters we find that an E(B-V)=0.24 and (m-M).
- ID:
- ivo://CDS.VizieR/J/AZh/79/867
- Title:
- Abundances of HII regions in blue galaxies
- Short Name:
- J/AZh/79/867
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- New expression for the ionization correction factors (ICF) are used to find the nebular-gas compositions in HII regions in blue compact dwarf galaxies (BCD). The abundances of He, N, O, Ne, S, and Ar in 41 HII regions are determined.
- ID:
- ivo://CDS.VizieR/J/MNRAS/422/2969
- Title:
- Abundances of 19 K-type giants in moving groups
- Short Name:
- J/MNRAS/422/2969
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the stellar parameters of 19 K-type giants and their abundances for 13 chemical elements (Al, Ba, Ca, Fe, K, Mg, Mn, Na, Ni, Sc, Si, Ti and V), selected from two moving groups, covering the metallicity range of -0.6<[Fe/H]<0.2, based on high-resolution spectra. Most of the elemental abundances show similar trends as in previous studies, except for Al, Na and Ba, which are seriously affected by evolution. The abundance ratios of [Na/Mg] increase smoothly with higher [Mg/H], and those of [Al/Mg] decrease slightly with increasing [Mg/H]. The abundance ratios of [Mg/Ba] show a distinction between these two moving groups, which is mainly induced by chemical evolution and also partly by kinematic effects. The inhomogeneous metallicity of each star from the moving groups demonstrates that these stars had different chemical origins before they were kinematically aggregated. This favours a dynamical resonant theory.
- ID:
- ivo://CDS.VizieR/J/ApJ/836/5
- Title:
- Abundances of LAMOST giants from APOGEE DR12
- Short Name:
- J/ApJ/836/5
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In this era of large-scale spectroscopic stellar surveys, measurements of stellar attributes ("labels," i.e., parameters and abundances) must be made precise and consistent across surveys. Here, we demonstrate that this can be achieved by a data-driven approach to spectral modeling. With The Cannon, we transfer information from the APOGEE survey to determine precise T_eff_, logg, [Fe/H], and [{alpha}/M] from the spectra of 450000 LAMOST giants. The Cannon fits a predictive model for LAMOST spectra using 9952 stars observed in common between the two surveys, taking five labels from APOGEE DR12 as ground truth T_eff_, logg, [Fe/H], [{alpha}/M], and K-band extinction A_k_. The model is then used to infer T_eff_, logg, [Fe/H], and [{alpha}/M] for 454180 giants, 20% of the LAMOST DR2 stellar sample. These are the first [{alpha}/M] values for the full set of LAMOST giants, and the largest catalog of [{alpha}/M] for giant stars to date. Furthermore, these labels are by construction on the APOGEE label scale; for spectra with S/N>50, cross-validation of the model yields typical uncertainties of 70K in T_eff_, 0.1 in logg, 0.1 in [Fe/H], and 0.04 in [{alpha}/M], values comparable to the broadly stated, conservative APOGEE DR12 uncertainties. Thus, by using "label transfer" to tie low-resolution (LAMOST R~1800) spectra to the label scale of a much higher-resolution (APOGEE R~22500) survey, we substantially reduce the inconsistencies between labels measured by the individual survey pipelines. This demonstrates that label transfer with The Cannon can successfully bring different surveys onto the same physical scale.
