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2771. Chemical analysis of CH stars
ID:
ivo://CDS.VizieR/J/MNRAS/440/1095
Title:
Chemical analysis of CH stars
Short Name:
J/MNRAS/440/1095
Date:
21 Oct 2021
Publisher:
CDS
Description:
Results from high-resolution spectral analyses of a selected sample of CH stars are presented. Detailed chemical composition studies of these objects, which could reveal abundance patterns that in turn provide information regarding nucleosynthesis and evolutionary status, are scarce in the literature. We conducted detailed chemical composition studies for these objects based on high-resolution (R~42000) spectra. The spectra were taken from the ELODIE archive and cover the wavelength range from 3900 to 6800{AA}. We estimated the stellar atmospheric parameters, the effective temperature T_eff_, the surface gravity logg, and the metallicity [Fe/H] from local thermodynamic equilibrium analyses using model atmospheres. Estimated temperatures of these objects cover a wide range, from 4550 to 6030K. The surface gravity ranges from 1.8 to 3.8, and the metallicity from -0.18 to -1.4. We report updates on elemental abundances for several heavy elements and present estimates of abundance ratios for Sr, Y, Zr, Ba, La, Ce, Pr, Nd, Sm, Eu and Dy with respect to Fe. For the object HD 188650 we present the first abundance analysis results based on a high-resolution spectrum. Enhancements of heavy elements relative to Fe, which are characteristic of CH stars, are evident from our analyses for most of the objects. A parametric model-based study was performed to understand the relative contributions from the s- and r-processes to the abundances of the heavy elements.
2772. Chemical analysis of CH stars. II.
ID:
ivo://CDS.VizieR/J/MNRAS/446/2348
Title:
Chemical analysis of CH stars. II.
Short Name:
J/MNRAS/446/2348
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present detailed chemical analyses for a sample of 12 stars selected from the CH star catalogue of Bartkevicius (1996BaltA...5..217B). The sample includes two confirmed binaries, four objects that are known to show radial velocity variations and the rest with no information on the binary status. A primary objective is to examine if all these objects exhibit chemical abundances characteristics of CH stars, based on detailed chemical composition study using high-resolution spectra. We have used high-resolution (R~42000) spectra from the ELODIE archive (Moultaka et al. 2004PASP..116..693M). These spectra cover 3900 to 6800 {AA} in the wavelength range. We have estimated the stellar atmospheric parameters, the effective temperature T_eff_, the surface gravity log g, and metallicity [Fe/H] from local thermodynamic equilibrium analysis using model atmospheres. Estimated temperatures of these objects cover a wide range from 4200 to 6640 K, the surface gravity from 0.6 to 4.3 and metallicity from -0.13 to -1.5. We report updates on elemental abundances for several heavy elements, Sr, Y, Zr, Ba, La, Ce, Pr, Nd, Sm, Eu and Dy. For the object HD 89668, we present the first abundance analyses results. Enhancement of heavy elements relative to Fe, a characteristic property of CH stars is evident from our analyses in the case of four objects, HD 92545, HD 104979, HD 107574 and HD 204613. A parametric-model-based study is performed to understand the relative contributions from the s- and r-process to the abundances of the heavy elements.
2773. Chemical analysis of early-type stars with planets
ID:
ivo://CDS.VizieR/J/A+A/647/A49
Title:
Chemical analysis of early-type stars with planets
Short Name:
J/A+A/647/A49
Date:
21 Oct 2021
Publisher:
CDS
Description:
We performed a detailed abundance determination in a sample of early-type stars with and without planets via spectral synthesis, searching for a likely relation between lambda Bootis stars and the presence of planets. We found no unique chemical pattern for the group of early-type stars bearing giant planets. However, our results support, in principle, a suggested scenario in which giant planets orbiting pre-main-sequence stars possibly block the dust of the disk and result in a lambda Bootis-like pattern. On the other hand, we do not find a lambda Bootis pattern in different hot-Jupiter planet host stars, which does not support the idea of possible accretion from the winds of hot-Jupiters, recently proposed in the literature. As a result, other mechanisms should account for the presence of the lambda Bootis pattern between main-sequence stars. Finally, we suggest that the formation of planets around lambda Bootis stars, such as HR 8799 and HD 169142, is also possible through the core accretion process and not only gravitational instability.
2774. Chemical analysis of NGC 4636 globular clusters
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.
2775. Chemical anomalies in old LMC clusters
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.
2776. Chemical composition of globular cluster NGC 6426
ID:
ivo://CDS.VizieR/J/A+A/599/A97
Title:
Chemical composition of globular cluster NGC 6426
Short Name:
J/A+A/599/A97
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present our detailed spectroscopic analysis of the chemical composition of four red giant stars in the halo globular cluster NGC 6426. We obtained high-resolution spectra using the Magellan2/MIKE spectrograph, from which we derived equivalent widths and subsequently computed abundances of 24 species of 22 chemical elements. For the purpose of measuring equivalent widths, we developed a new semi-automated tool, called EWCODE. We report a mean Fe content of [Fe/H]=-2.34+/-0.05dex (stat.) in accordance with previous studies. At a mean {alpha}-abundance of [(Mg,Si,Ca)/3Fe]=0.39+/-0.03dex, NGC 6426 falls on the trend drawn by the Milky Way halo and other globular clusters at comparably low metallicities. The distribution of the lighter {alpha}-elements as well as the enhanced ratio [Zn/Fe]=0.39dex could originate from hypernova enrichment of the pre-cluster medium. We find tentative evidence for a spread in the elements Mg, Si, and Zn, indicating an enrichment scenario, where ejecta of evolved massive stars of a slightly older population polluted a newly born younger one. The heavy element abundances in this cluster fit well into the picture of metal-poor globular clusters, which in that respect appear to be remarkably homogeneous. The pattern of the neutron-capture elements heavier than Zn point towards an enrichment history governed by the r-process with only little - if any - sign of s-process contributions. This finding is supported by the striking similarity of our program stars to the metal-poor field star HD 108317.
2777. Chemical composition of halo and disk stars
ID:
ivo://CDS.VizieR/J/A+AS/141/491
Title:
Chemical composition of halo and disk stars
Short Name:
J/A+AS/141/491
Date:
21 Oct 2021
Publisher:
CDS
Description:
Table 3. Atmospheric parameters, space velocities, distances, masses and ages of the program stars. Table 4. Atomic line data including wavelength, excitation energy of the lower level, the logarithm of the oscillator strength (the experimental or theoretical value, the corrected value and the differential value from standard stars) and the adopted enhancement factor of the Unsold approximation to the van der Waals damping constant. The last column gives the equivalent width in the spectrum of HD 142373 representing a typical metallicity of the sample of stars. Uncertain EWs marked by (:) and strong lines with EW>100m{AA} are not used in the abundance determination for this star. Table 5. Abundance ratios for the program stars. The oxygen abundance is derived from the 7774{AA} triplet but scaled to results from the forbidden [OI] line at 6300{AA}.
2778. Chemical composition of halo and disk stars
ID:
ivo://CDS.VizieR/J/A+A/326/751
Title:
Chemical composition of halo and disk stars
Short Name:
J/A+A/326/751
Date:
21 Oct 2021
Publisher:
CDS
Description:
Table A1 lists the Stromgren photometry together with color excesses, E(b-y), photometric metallicities, [Fe/H] , calculated from the calibrations of Schuster & Nissen (1989A&A...221...65S), and absolute magnitudes, M(V), and distances derived with the equations of Nissen & Schuster (1991A&A...251..457N) using the photometric metallicities. Table A2 contains coordinates, proper motions and radial velocities for the program stars as well as distances calculated from the calibrations Nissen & Schuster (1991A&A...251..457N) using the spectroscopic metallicities scaled to our photometric [Fe/H] system. Table A3 gives a list of the 209 spectral lines, which were analyzed, arranged element by element. The table contains the wavelength, the excitation potential of the lower level corresponding to the line, the gf-value, the enhancement factor of the classical van der Waals damping constant, the statistical weight of the upper level, and the equivalent widths measured for the two "standard" stars, HD 22879 and HD 76932. Table A4 contains the measured equivalent widths for all program stars. Table A5 gives abundance ratios and kinematical as well as orbital parameters for the program stars. First are given the data for the 16 disk stars, then follows the 14 halo stars.
2779. Chemical composition of LMC red giants
ID:
ivo://CDS.VizieR/J/AJ/136/375
Title:
Chemical composition of LMC red giants
Short Name:
J/AJ/136/375
Date:
21 Oct 2021
Publisher:
CDS
Description:
This paper presents the chemical abundance analysis of a sample of 27 red giant stars located in four populous intermediate-age globular clusters in the Large Magellanic Cloud, namely NGC 1651, 1783, 1978, and 2173. This analysis is based on high-resolution (R~47000) spectra obtained with the UVES@VLT spectrograph. For each cluster we derived up to 20 abundance ratios sampling the main chemical elemental groups, namely light odd-Z, {alpha} iron-peak, and neutron-capture elements.
2780. Chemical composition of old LMC clusters
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.

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