- ID:
- ivo://CDS.VizieR/J/ApJ/655/492
- Title:
- Equivalent widths of 26 metal-poor stars
- Short Name:
- J/ApJ/655/492
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The chemical compositions of 26 metal-poor stars that exhibit strong CH and/or C2 molecular bands are determined. Twenty-two stars in our sample satisfy our definition for carbon-enhanced metal-poor (CEMP) stars based on the carbon abundance ratio ([C/Fe]) and the evolutionary status. In addition, we measure Na abundances for nine known carbon-enhanced stars. Combining our new sample with the results of previous work, we investigate the abundance and evolutionary status of a total of 64 CEMP stars.
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Search Results
- ID:
- ivo://CDS.VizieR/J/ApJ/769/57
- Title:
- Equivalent widths of metal-poor stars
- Short Name:
- J/ApJ/769/57
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- It is well established that stellar effective temperatures determined from photometry and spectroscopy yield systematically different results. We describe a new, simple method to correct spectroscopically derived temperatures ("excitation temperatures") of metal-poor stars based on a literature sample with -3.3<[Fe/H]<-2.5. Excitation temperatures were determined from Fe I line abundances in high-resolution optical spectra in the wavelength range of ~3700-7000{AA}, although shorter wavelength ranges, up to 4750-6800{AA}, can also be employed, and compared with photometric literature temperatures. Our adjustment scheme increases the temperatures up to several hundred degrees for cool red giants, while leaving the near-main-sequence stars mostly unchanged. Hence, it brings the excitation temperatures in good agreement with photometrically derived values. The modified temperature also influences other stellar parameters, as the Fe I-Fe II ionization balance is simultaneously used to determine the surface gravity, while also forcing no abundance trend on the absorption line strengths to obtain the microturbulent velocity. As a result of increasing the temperature, the often too low gravities and too high microturbulent velocities in red giants become higher and lower, respectively. Our adjustment scheme thus continues to build on the advantage of deriving temperatures from spectroscopy alone, independent of reddening, while at the same time producing stellar chemical abundances that are more straightforwardly comparable to studies based on photometrically derived temperatures. Hence, our method may prove beneficial for comparing different studies in the literature as well as the many high-resolution stellar spectroscopic surveys that are or will be carried out in the next few years.
- ID:
- ivo://CDS.VizieR/J/MNRAS/422/3527
- Title:
- Equivalent widths of 11 NGC 3680 stars
- Short Name:
- J/MNRAS/422/3527
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a new abundance analysis of the intermediate-age Galactic open cluster NGC 3680, based on high-resolution, high signal-to-noise ratio VLT/UVES spectroscopic data. Several element abundances are presented for this cluster for the first time, but most notably we derive abundances for the light and heavy s-process elements Y, Ba, La and Nd. The serendipitous measurement of the rare-earth r-process element Gd is also reported. This cluster exhibits a significant enhancement of Na in giants as compared to dwarfs, which may be a proxy for an O to Na anticorrelation as observed in Galactic globular clusters but not open clusters. We also observe a step-like enhancement of heavy s-process elements towards higher atomic number, contrary to expectations from asymptotic giant branch nucleosynthesis models, suggesting that the r process played a significant role in the generation of both La and Nd in this cluster.
- ID:
- ivo://CDS.VizieR/J/MNRAS/435/3667
- Title:
- Equivalent widths of 6 NGC5694 stars
- Short Name:
- J/MNRAS/435/3667
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of the analysis of high-resolution spectra obtained with UVES-FLAMES at the Very Large Telescope for six red giant branch stars in the outer-halo metal-poor ([Fe/H]I=-1.98 and [Fe/H]II=-1.83) Galactic globular cluster NGC 5694, which has been suggested as a possible incomer by Lee et al. based on the anomalous chemical composition of a single cluster giant. We obtain accurate abundances for a large number of elements and we find that (a)the six target stars have the same chemical composition within the uncertainties, except for Na and Al; (b) the average cluster abundance of {alpha} elements (with the only exception of Si) is nearly solar, at odds with typical halo stars and globular clusters of similar metallicity; (c) Y, Ba, La and Eu abundances are also significantly lower than in Galactic field stars and star clusters of similar metallicity. Hence, we confirm the Lee et al. classification of NGC 5694 as a cluster of extragalactic origin. We provide the first insight on the Na-O and Mg-Al anticorrelations in this cluster: all the considered stars have very similar abundance ratios for these elements, except one that has significantly lower [Na/Fe] and [Al/Fe] ratios, suggesting that some degree of early self-enrichment has occurred also in this cluster.
- ID:
- ivo://CDS.VizieR/J/ApJ/613/129
- Title:
- Equivalent widths of QSOs
- Short Name:
- J/ApJ/613/129
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of a search for variability in the equivalent widths (EWs) of narrow, associated (|{Delta}v|<=5000km/s) absorption lines found in the UV spectra of z<=1.5 quasars. The goal of this search was to use variability as a means of identifying absorption lines arising in gas that is intrinsic to the quasar central engine. We have compared archival Hubble Space Telescope (HST) Faint Object Spectrograph (FOS) spectra of quasars with recent spectra obtained as part of our own snapshot survey of the same objects with the Space Telescope Imaging Spectrograph (STIS). The intervals between observations are 4-10yr. We primarily focused on the C IV absorption lines, although we also studied other lines available in the same spectra (e.g., Ly{alpha}, N V, O VI).
- ID:
- ivo://CDS.VizieR/J/PAZh/38/122
- Title:
- Equivalent widths of 14 red giants
- Short Name:
- J/PAZh/38/122
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The results of a comparative analysis of the elemental abundances in the atmospheres of 14 red giants with high Galactic space velocities are presented. For almost all of the chemical elements considered, the their abundance trends with metallicity correspond to those constructed for thick-disk dwarfs. In the case of sodium, the main factor affecting the [Na/Fe] abundance in the stellar atmosphere for red giants is the surface gravity that characterizes the degree of development of the convective envelope. The difference between the [Na/Fe] abundances in the atmospheres of thin- and thick-disk red giants has been confirmed.
- ID:
- ivo://CDS.VizieR/J/A+A/615/A165
- Title:
- Equivalent widths of 13 red giants in IC 4756
- Short Name:
- J/A+A/615/A165
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Homogeneous investigations of red giant stars in open clusters contribute to studies of internal evolutionary mixing processes inside stars, which are reflected in abundances of mixing-sensitive chemical elements like carbon, nitrogen, and sodium, while {alpha}- and neutron-capture element abundances are useful in tracing the Galactic chemical evolution. The main aim of this study is a comprehensive chemical analysis of red giant stars in the open cluster IC 4756, including determinations of ^12^C/^13^C and C/N abundance ratios, and comparisons of the results with theoretical models of stellar and Galactic chemical evolution. We used a classical differential model atmosphere method to analyse high-resolution spectra obtained with the FEROS spectrograph on the 2.2m MPG/ESO Telescope. The carbon, nitrogen, and oxygen abundances, ^12^C/^13^C ratios, and neutron-capture element abundances were determined using synthetic spectra, and the main atmospheric parameters and abundances of other chemical elements were determined from equivalent widths of spectral lines.
- ID:
- ivo://CDS.VizieR/J/AJ/139/1942
- Title:
- Equivalent widths of red giants in 6 open clusters
- Short Name:
- J/AJ/139/1942
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a detailed abundance analysis based on high resolution spectroscopy for 16 stars in the old open clusters Be 31, Be 32, Be 39, M 67, NGC 188, and NGC 1193.
- ID:
- ivo://CDS.VizieR/J/ApJ/751/102
- Title:
- Equivalent widths of 9 RGB in Carina dSph
- Short Name:
- J/ApJ/751/102
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The detailed abundances of 23 chemical elements in nine bright red giant branch stars in the Carina dwarf spheroidal galaxy are presented based on high-resolution spectra gathered at the Very Large Telescope (VLT) and Magellan telescopes. A spherical model atmospheres analysis is applied using standard methods (local thermodynamic equilibrium and plane-parallel radiative transfer) to spectra ranging from 380 to 680nm. Stellar parameters are found to be consistent between photometric and spectroscopic analyses, both at moderate and high resolution. The stars in this analysis range in metallicity from -2.9<[Fe/H]<-1.3, and adopting the ages determined by Lemasle et al. (Cat. J/A+A/538/A100), we are able to examine the chemical evolution of Carina's old and intermediate-aged populations.
- ID:
- ivo://CDS.VizieR/J/ApJ/804/109
- Title:
- Equivalent widths of RGB stars in NGC 5053
- Short Name:
- J/ApJ/804/109
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- NGC 5053 provides a rich environment to test our understanding of the complex evolution of globular clusters (GCs). Recent studies have found that this cluster has interesting morphological features beyond the typical spherical distribution of GCs, suggesting that external tidal effects have played an important role in its evolution and current properties. Additionally, simulations have shown that NGC 5053 could be a likely candidate to belong to the Sagittarius dwarf galaxy (Sgr dSph) stream. Using the Wisconsin-Indiana-Yale-NOAO-Hydra multi-object spectrograph, we have collected high quality (signal-to-noise ratio ~75-90), medium-resolution spectra for red giant branch stars in NGC 5053. Using these spectra we have measured the Fe, Ca, Ti, Ni, Ba, Na, and O abundances in the cluster. We measure an average cluster [Fe/H] abundance of -2.45 with a standard deviation of 0.04 dex, making NGC 5053 one of the most metal-poor GCs in the Milky Way (MW). The [Ca/Fe], [Ti/Fe], and [Ba/Fe] we measure are consistent with the abundances of MW halo stars at a similar metallicity, with alpha-enhanced ratios and slightly depleted [Ba/Fe]. The Na and O abundances show the Na-O anti-correlation found in most GCs. From our abundance analysis it appears that NGC 5053 is at least chemically similar to other GCs found in the MW. This does not, however, rule out NGC 5053 being associated with the Sgr dSph stream.