- 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.
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Search Results
- 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/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.
- ID:
- ivo://CDS.VizieR/J/AJ/161/128
- Title:
- Chemical composition of 15 red giant stars with HPF
- Short Name:
- J/AJ/161/128
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have used the Habitable Zone Planet Finder (HPF) to gather high-resolution, high signal-to-noise near-infrared spectra of 13 field red horizontal branch (RHB) stars, one open cluster giant, and one very metal-poor halo red giant. The HPF spectra cover the 0.81-1.28{mu}m wavelength range of the zyJ bands, partially filling the gap between the optical (0.4-1.0{mu}m) and infrared (1.5-2.4{mu}m) spectra already available for the program stars. We derive abundances of 17 species from LTE-based computations involving equivalent widths and spectrum syntheses, and estimate abundance corrections for the species that are most affected by departures from LTE in RHB stars. Generally good agreement is found between HPF-based metallicities and abundance ratios and those from the optical and infrared spectral regions. Light element transitions dominate the HPF spectra of these red giants, and HPF data can be used to derive abundances from species with poor or no representation in optical spectra (e.g., C i, P i, S i, K i). Attention is drawn to the HPF abundances in two field solar-metallicity RHB stars of special interest: one with an extreme carbon isotope ratio, and one with a rare, very large lithium content. The latter star is unique in our sample in exhibiting very strong He i 10830{AA} absorption. The abundances of the open cluster giant concur with those derived from other wavelength regions. Detections of CI and SI in HD122563 are reported, yielding the lowest metallicity determination of [S/Fe] from more than one multiplet.
- ID:
- ivo://CDS.VizieR/J/A+A/619/A176
- Title:
- Chemical composition of Ruprecht 147
- Short Name:
- J/A+A/619/A176
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Ruprecht 147 (NGC 6774) is the closest old open cluster, with a distance of less than 300pc and an age of about 2.5Gyr. It is therefore well suited for testing stellar evolution models and for obtaining precise and detailed chemical abundance information. We combined photometric and astrometric information coming from literature and the Gaia mission with very high-resolution optical spectra of stars in different evolutionary stages to derive the cluster distance, age, and detailed chemical composition. We obtained spectra of six red giants using HARPS-N at the Telescopio Nazionale Galileo (TNG). We also used European Southern Observatory (ESO) archive spectra of 22 main sequence (MS) stars, observed with HARPS at the 3.6m telescope. The very high resolution (115000) and the large wavelength coverage (about 380-680nm) of the twin instruments permitted us to derive atmospheric parameters, metallicity, and detailed chemical abundances of 23 species from all nucleosynthetic channels. We employed both equivalent widths and spectrum synthesis. We also re-derived the cluster distance and age using Gaia parallaxes, proper motions, and photometry in conjunction with the PARSEC stellar evolutionary models. We fully analysed those stars with radial velocity and proper motion/parallax in agreement with the cluster mean values. We also discarded one binary not previously recognised, and six stars near the MS turn-off because of their high rotation velocity. Our final sample consists of 21 stars (six giants and 15 MS stars). We measured metallicity (the cluster average [Fe/H] is +0.08, rms=0.07) and abundances of light, alpha, Fe-peak, and neutron-capture elements. The Li abundance follows the expectations, showing a tight relation between temperature and abundance on the MS, at variance with M67, and we did not detect any Li-rich giant.
- ID:
- ivo://CDS.VizieR/J/ApJ/706/1095
- Title:
- Chemical compositions of 26 outer halo stars
- Short Name:
- J/ApJ/706/1095
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Chemical abundances of 26 metal-poor dwarfs and giants are determined from high-resolution and high signal-to-noise ratio spectra obtained with the Subaru/High Dispersion Spectrograph. The sample is selected so that most of the objects have outer-halo kinematics. Self-consistent atmospheric parameters were determined by an iterative procedure based on spectroscopic analysis. Abundances of 13 elements, including {alpha}-elements (Mg, Si, Ca, Ti), odd-Z light elements (Na, Sc), iron-peak elements (Cr, Mn, Fe, Ni, Zn), and neutron-capture elements (Y, Ba), are determined by two independent data reduction and local thermodynamic equillibrium analysis procedures, confirming the consistency of the stellar parameters and abundances results.
- ID:
- ivo://CDS.VizieR/J/ApJS/197/29
- Title:
- Chemical compositions of 11 RR Lyrae
- Short Name:
- J/ApJS/197/29
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a detailed abundance study of 11 RR Lyrae ab-type variables: AS Vir, BS Aps, CD Vel, DT Hya, RV Oct, TY Gru, UV Oct, V1645 Sgr, WY Ant, XZ Aps, and Z Mic. High-resolution and high signal-to-noise ratio echelle spectra of these variables were obtained with the 2.5m du Pont telescope at the Las Campanas Observatory. We obtained more than 2300 spectra, roughly 200 spectra per star, distributed more or less uniformly throughout the pulsational cycles. A new method has been developed to obtain the initial effective temperatures of our sample stars at a specific pulsational phase. We find that the abundance ratios are generally consistent with those of similar metallicity field stars in different evolutionary states and throughout the pulsational cycles for RR Lyrae stars. TY Gru remains the only n-capture enriched star among the RRab in our sample.
- ID:
- ivo://CDS.VizieR/J/A+A/472/101
- Title:
- Chemical evolution of SMC planetary nebulae
- Short Name:
- J/A+A/472/101
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We investigate the chemical evolution of the Small Magellanic Cloud (SMC) based on abundance data of planetary nebulae (PNe). The main goal is to investigate the time evolution of the oxygen abundance in this galaxy by deriving an age-metallicity relation. Such a relation is of fundamental importance as an observational constraint for chemical evolution models of the SMC. We have used high quality PNe data to derive the properties of the progenitor stars, so that the stellar ages could be estimated. We collected a large number of measured spectral fluxes for each nebula and derived accurate physical parameters and nebular abundances. New spectral data for a sample of SMC PNe obtained between 1999 and 2002 are also presented. These data are used with data available in the literature to improve the accuracy of the fluxes for each spectral line.
- ID:
- ivo://CDS.VizieR/J/A+A/527/A88
- Title:
- Chemistry in infrared dark clouds
- Short Name:
- J/A+A/527/A88
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Massive stars play an important role in shaping the structure of galaxies. Infrared dark clouds (IRDCs), with their low temperatures and high densities, have been identified as the potential birthplaces of massive stars. In order to understand the formation processes of massive stars, the physical and chemical conditions in infrared dark clouds have to be characterized. The goal of this paper is to investigate the chemical composition of a sample of southern infrared dark clouds. One important aspect of the observations is to check, whether the molecular abundances in IRDCs are similar to the low-mass pre-stellar cores, or if they show signatures of more evolved evolutionary stages. We performed observations toward 15 IRDCs in the frequency range between 86 and 93GHz using the 22-m Mopra radio telescope. In total, 13 molecular species comprising N_2_H^+^, ^13^CS, CH_3_CN, HC_3_N, HNC, HCO^+^, HCN, HNCO, C_2_H, SiO, H^13^CO^+^, H^13^CN, and CH_3_C_2_H were observed for all targets. Hence, we included in general species appropriate for elevated densities, where some of them trace the more quiescent gas, while others are sensitive to more dynamical processes.
