- ID:
- ivo://CDS.VizieR/J/A+A/562/A71
- Title:
- Chemical abundances of solar neighbourhood dwarfs
- Short Name:
- J/A+A/562/A71
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a detailed elemental abundance study of 714 F and G dwarf and subgiant stars in the Solar neighbourhood. The analysis is based on high-resolution spectra obtained with MIKE on the Magellan telescope, FEROS on the ESO 1.5m and 2.2m telescopes, HARPS on the ESO 3.6m telescope, UVES on the ESO Very Large Telescope, SOFIN and FIES on the Nordic Optical Telescope. Our data show that there is an old and alpha-enhanced disk population, and a younger and less alpha-enhanced disk population. While they overlap greatly in metallicity between -0.7<[Fe/H]<+0.1, they show a bimodal distribution in [alpha/Fe]. This bimodality becomes even clearer if stars where stellar parameters and abundances show larger uncertainties (Teff<5400K) are discarded, showing that it is important to constrain the data set to a narrow range in the stellar parameters if small differences between stellar populations are to be revealed. In addition, we find that the alpha-enhanced population has orbital parameters placing the stellar birthplaces in the inner Galactic disk while the low-alpha stars mainly come from the outer Galactic disk, fully consistent with the recent claims of a short scale-length for the alpha-enhanced Galactic thick disk. We have also investigated the properties of the Hercules stream and the Arcturus moving group.
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- ID:
- ivo://CDS.VizieR/J/ApJ/808/42
- Title:
- CHemical Abundances of Spirals (CHAOS) II. M51
- Short Name:
- J/ApJ/808/42
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have observed NGC 5194 (M51a) as part of the CHemical Abundances of Spirals project (CHAOS). Using the Multi Object Double Spectrographs on the Large Binocular Telescope we are able to measure one or more of the temperature-sensitive auroral lines ([OIII]{lambda}4363, [NII]{lambda}5755, [SIII]{lambda}6312) and thus measure "direct" gas-phase abundances in 29 individual HII regions. [OIII]{lambda}4363 is only detected in two HII regions, both of which show indications of excitation by shocks. We compare our data to previous direct abundances measured in NGC 5194 and find excellent agreement ({Delta}[log(O/H)]~0.05) for all but one region. We find no evidence of trends in Ar/O, Ne/O, or S/O within NGC 5194 or compared to other galaxies. We find modest negative gradients in both O/H and N/O with very little scatter ({sigma}<=0.08dex), most of which can be attributed to random error and not to intrinsic dispersion. The gas-phase abundance gradient is consistent with the gradients observed in other interacting galaxies, which tend to be shallower than gradients measured in isolated galaxies. The N/O ratio (<log(N/O)>=-0.62) suggests secondary nitrogen production is responsible for a significantly larger fraction of nitrogen (e.g., factor of 8-10), relative to primary production mechanisms than predicted by theoretical models.
- ID:
- ivo://CDS.VizieR/J/ApJ/806/16
- Title:
- CHemical Abundances of Spirals (CHAOS). I. NGC628
- Short Name:
- J/ApJ/806/16
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The CHemical Abundances of Spirals (CHAOS) project leverages the combined power of the Large Binocular Telescope (LBT) with the broad spectral range and sensitivity of the Multi Object Double Spectrograph (MODS) to measure "direct" abundances (based on observations of the temperature-sensitive auroral lines) in large samples of HII regions in spiral galaxies. We present LBT MODS observations of 62 HII regions in the nearby spiral galaxy NGC 628, with an unprecedentedly large number of auroral lines measurements (18 [OIII]{lambda}4363, 29 [NII]{lambda}5755, 40 [SIII]{lambda}6312, and 40 [OII]{lambda}{lambda}7320,7330 detections) in 45 HII regions. We conduct a uniform abundance analysis prioritizing the temperatures derived from [SIII]{lambda}6312 and [NII]{lambda}5755, and report the gas-phase abundance gradients for NGC 628. Relative abundances of S/O, Ne/O, and Ar/O are constant across the galaxy, consistent with no systematic change in the upper IMF over the sampled range in metallicity. These alpha-element ratios, along with N/O, all show small dispersions ({sigma}~0.1dex) over 70% of the azimuthally averaged radius. We interpret these results as an indication that, at a given radius, the interstellar medium in NGC 628 is chemically well-mixed. Unlike the gradients in the nearly temperature-independent relative abundances, O/H abundances have a larger intrinsic dispersion of ~0.165dex. We posit that this dispersion represents an upper limit to the true dispersion in O/H at a given radius and that some of that dispersion is due to systematic uncertainties arising from temperature measurements.
- ID:
- ivo://CDS.VizieR/J/ApJ/759/116
- Title:
- Chemical analysis of NGC 4636 globular clusters
- Short Name:
- J/ApJ/759/116
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a spectroscopic analysis of the metallicities, ages, and alpha-elements of the globular clusters (GCs) in the giant elliptical galaxy (gE) NGC 4636 in the Virgo Cluster. Line indices of the GCs are measured from the integrated spectra obtained with Faint Object Camera and Spectrograph on the Subaru 8.2m Telescope. We derive [Fe/H] values of 59 GCs based on the Brodie & Huchra (1990ApJ...362..503B) method, and [Z/H], age, and [{alpha}/Fe] values of 33 GCs from the comparison of the Lick line indices with single stellar population models. The metallicity distribution of NGC 4636 GCs shows a hint of a bimodality with two peaks at [Fe/H]=-1.23({sigma}=0.32) and -0.35({sigma}=0.19). The age spread is large from 2Gyr to 15Gyr and the fraction of young GCs with age <5Gyr is about 27%. The [{alpha}/Fe] of the GCs shows a broad distribution with a mean value [{alpha}/Fe]{approx}0.14dex. The dependence of these chemical properties on the galactocentric radius is weak. We also derive the metallicities, ages, and [{alpha}/Fe] values for the GCs in other nearby gEs (M87, M49, M60, NGC 5128, NGC 1399, and NGC 1407) from the line index data in the literature using the same methods as used for NGC 4636 GCs. The metallicity distribution of GCs in the combined sample of seven gEs including NGC 4636 is found to be bimodal, supported by the KMM test with a significance level of >99.9%. All these gEs harbor some young GCs with ages less than 5Gyr. The mean age of the metal-rich GCs ([Fe/H]>-0.9) is about 3Gyr younger than that of the metal-poor GCs. The mean value of [{alpha}/Fe] of the gE GCs is smaller than that of the Milky Way GCs. We discuss these results in the context of GC formation in gEs.
- ID:
- ivo://CDS.VizieR/J/ApJ/695/L134
- Title:
- Chemical anomalies in old LMC clusters
- Short Name:
- J/ApJ/695/L134
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- By using the multifiber spectrograph FLAMES mounted at the ESO-VLT, we have obtained high-resolution spectra for 18 giant stars, belonging to three old globular clusters of the Large Magellanic Cloud (namely NGC 1786, 2210, and 2257). While stars in each cluster showed quite homogeneous iron content, within a few cents of dex (the mean values being [Fe/H]=-1.75+/-0.01dex, -1.65+/-0.02dex and -1.95+/-0.02dex for NGC 1786, 2210, and 2257, respectively), we have detected significant inhomogeneities for the [Na/Fe], [Al/Fe], [O/Fe], and [Mg/Fe] abundance ratios, with evidence of [O/Fe] versus [Na/Fe] and [Mg/Fe] versus [Al/Fe] anticorrelations. The trends detected nicely agree with those observed in Galactic Globular Clusters, suggesting that such abundance anomalies are ubiquitous features of old stellar systems and they do not depend on the parent galaxy environment. In NGC 1786 we also detected two extreme O-poor, Na-rich stars. This is the first time that a firm signature of extreme chemical abundance anomalies has been found in an extragalactic stellar cluster.
- ID:
- ivo://CDS.VizieR/J/A+A/281/465
- Title:
- Chemical Composition of alf UMi and V473 Lyr
- Short Name:
- J/A+A/281/465
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The spectrograms of the s-Cepheids alpha-UMi and HR 7308, taken at reciprocal dispersion of 9 A/mm with the Main Stellar Spectrograph at the Special Astrophysical Observatory's 6-m telescope, were analysed for determining chemical elements abundance. The results include the equivalent width, and the abundances in the two stars.
- ID:
- ivo://CDS.VizieR/J/MNRAS/359/865
- Title:
- Chemical composition of delta Sct
- Short Name:
- J/MNRAS/359/865
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present chemical abundances in the photosphere of delta Scuti (delta Sct) - a prototype of the class of pulsating variables - determined from the analysis of a spectrum obtained by using the 2-m telescope at the Peak Terskol Observatory and a high-resolution spectrometer with R=52000, a signal-to-noise ratio 250 and from International Ultraviolet Explorer spectra. The abundance pattern of delta Sct consists of 49 chemical elements. The abundances of 19 elements have not been investigated previously. The abundances of Pr and Nd obtained from the lines of the second and third spectra are equal. The abundances of heavy elements indicate the overabundances with respect to the solar system values up to 1dex. The abundance pattern of delta Sct is similar to the abundance patterns of Am-Fm or delta Del type stars. A splitting of the cores of all clean lines is observed for the spectra of Sct and HD 57749. This can signify evidence of non-radial pulsations in these stars
- ID:
- ivo://CDS.VizieR/J/AZh/78/807
- Title:
- Chemical composition of eta Ser
- Short Name:
- J/AZh/78/807
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Table2 contains the results of an analysis of elemental abundances in the atmosphere of eta Ser - a red giant of spectral type K2IIIabCN1. The resulting atmosphere parameters correspond to a K0 giant, and the peculiarities of the star chemical composition provide evidence that the assignment of Eta Ser to a class of CN stars was erroneous.
- ID:
- ivo://CDS.VizieR/J/ApJ/709/447
- Title:
- Chemical composition of OGLE-2007-BLG-514S
- Short Name:
- J/ApJ/709/447
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a high-resolution spectrum of a microlensed G dwarf in the Galactic bulge with spectroscopic temperature T_eff_=5600+/-180K. This I~21mag star was magnified by a factor ranging from 1160 to 1300 at the time of observation. Its high metallicity ([Fe/H]=0.33+/-0.15dex) places this star at the upper end of the bulge giant metallicity distribution. Using a Kolmogorov-Smirnov test, we find a 1.6% probability that the published microlensed bulge dwarfs share an underlying distribution with bulge giants, properly accounting for a radial bulge metallicity gradient. We obtain abundance measurements for 15 elements and perform a rigorous error analysis that includes covariances between parameters. This star, like bulge giants with the same metallicity, shows no alpha enhancement. It confirms the chemical abundance trends observed in previously analyzed bulge dwarfs. At supersolar metallicities, we observe a discrepancy between bulge giant and bulge dwarf Na abundances.
- ID:
- ivo://CDS.VizieR/J/ApJ/717/277
- Title:
- Chemical composition of old LMC clusters
- Short Name:
- J/ApJ/717/277
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- This paper presents the chemical abundance analysis of a sample of 18 giant stars in three old globular clusters in the Large Magellanic Cloud (LMC), NGC 1786, NGC 2210, and NGC 2257. The derived iron content is [Fe/H]=-1.75+/-0.01dex ({sigma}=0.02dex), -1.65+/-0.02dex ({sigma}=0.04dex), and -1.95+/-0.02dex ({sigma}=0.04dex) for NGC 1786, NGC 2210, and NGC 2257, respectively. All the clusters exhibit similar abundance ratios, with enhanced values (~+0.30dex) of [{alpha}/Fe], consistent with the Galactic halo stars, thus indicating that these clusters have formed from a gas enriched by Type II supernovae. We also found evidence that r-process is the main channel of production of the measured neutron capture elements (Y, Ba, La, Nd, Ce, and Eu). In particular, the quite large enhancement of [Eu/Fe] (~+0.70dex) found in these old clusters clearly indicates a relevant efficiency of the r-process mechanism in the LMC environment.
