- ID:
- ivo://CDS.VizieR/J/MNRAS/449/3889
- Title:
- Detailed abundances of 15 stars in NGC 4833
- Short Name:
- J/MNRAS/449/3889
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have observed 15 red giant stars in the relatively massive, metal-poor globular cluster NGC 4833 using the Magellan Inamori Kyocera Echelle spectrograph at Magellan. We calculate stellar parameters for each star and perform a standard abundance analysis to derive abundances of 43 species of 39 elements, including 20 elements heavier than the iron group. We derive <[Fe/H]>=-2.25+/-0.02 from FeI lines and <[Fe/H]>=-2.19+/-0.013 from FeII lines. We confirm earlier results that found no internal metallicity spread in NGC 4833, and there are no significant star-to-star abundance dispersions among any elements in the iron group (19=<Z=<30). We recover the usual abundance variations among the light elements C, N, O, Na, Mg, Al, and possibly Si. The heavy-element distribution reflects enrichment by r-process nucleosynthesis ([Eu/Fe]=+0.36+/-0.03), as found in many other metal-poor globular clusters. We investigate small star-to-star variations found among the neutron-capture elements, and we conclude that these are probably not real variations. Upper limits on the Th abundance, log{epsilon} (Th/Eu)<-0.47+/-0.09, indicate that NGC 4833, like other globular clusters where Th has been studied, did not experience a so-called actinide boost.
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Search Results
- ID:
- ivo://CDS.VizieR/J/A+A/557/A138
- Title:
- Detailed chemical abundances in the GlC NGC 362
- Short Name:
- J/A+A/557/A138
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We obtained FLAMES GIRAFFE+UVES spectra for both first and second-generation red giant branch (RGB) stars in the globular cluster (GC) NGC 362 and used them to derive abundances of 21 atomic species for a sample of 92 stars. The surveyed elements include proton-capture (O, Na, Mg, Al, Si), alpha-capture (Ca, Ti), Fe-peak (Sc, V, Mn, Co, Ni, Cu), and neutron-capture elements (Y, Zr, Ba, La, Ce, Nd, Eu, Dy). The analysis is fully consistent with that presented for twenty GCs in previous papers of this series. Stars in NGC 362 seem to be clustered into two discrete groups along the Na-O anti-correlation, with a gap at [O/Na]~0dex. Na-rich, second generation stars show a trend to be more centrally concentrated, although the level of confidence is not very high. When compared to the classical second-parameter twin NGC 288, with similar metallicity, but different horizontal branch type and much lower total mass, the proton-capture processing in stars of NGC 362 seems to be more extreme, confirming previous analysis. We discovered the presence of a secondary RGB sequence, redder than the bulk of the RGB: a preliminary estimate shows that this sequence comprises about 6% of RGB stars. Our spectroscopic data and literature photometry indicate that this sequence is populated almost exclusively by giants rich in Ba, and probably rich in all s-process elements, as found in other clusters. In this regards, NGC 362 joins previously studied GCs like NGC 1851, NGC 6656 (M 22), and NGC 7089 (M 2).
- ID:
- ivo://CDS.VizieR/J/A+A/635/A8
- Title:
- Differential abundances of open clusters
- Short Name:
- J/A+A/635/A8
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Well studied Open Clusters (OCs) of the Solar neighbourhood are frequently used as reference objects to test galactic and stellar theories. For that purpose their chemical composition needs to be known with a high level of confidence. It is also important to clarify if each OC is chemically homogeneous and if it has a unique chemical signature. The aims of this work are (1) to determine accurate and precise abundances of 22 chemical species (from Na to Eu) in the Hyades, Praesepe and Rupecht 147 using a large number of stars at different evolutionary states, (2) to evaluate the level of chemical homogeneity of these OCs, (3) to compare their chemical signatures. We gathered ~800 high resolution and high signal-to-noise spectra of ~100 members in the three clusters, obtained with the latest memberships based on Gaia DR2 data. We build a pipeline which computes atmospheric parameters and strictly line-by-line differential abundances among twin stars in our sample. With this method we are able to reach a very high precision in the abundances (0.01-0.02dex in most of the elements). We find large differences in the absolute abundances in some elements, which can be attributed to diffusion, NLTE effects or systematics in the analysis. For the three OCs, we find strong correlations in the differential abundances between different pairs of elements. According to our experiment with synthetic data, this can be explained by some level of chemical inhomogeneity. We compare differential abundances of several stars from the Hyades and Praesepe tails: the stars that differ more in chemical abundances also have distinct kinematics, even though they have been identified as members of the tail. It is possible to obtain high precision abundances using a differential analysis even when mixing spectra from different instruments. With this technique we find that the Hyades and Preasepe have the same chemical signature when G dwarfs and K giants are considered. Despite a certain level of inhomogeneity in each cluster, it is still possible to clearly distinguish the chemical signature of the older cluster Ruprecht 147 when compared to the Hyades and Praesepe.
- ID:
- ivo://CDS.VizieR/J/A+A/630/A104
- Title:
- Disk and halo stars C, O and Fe abundances
- Short Name:
- J/A+A/630/A104
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The abundances of carbon, oxygen, and iron in late-type stars are important parameters in exoplanetary and stellar physics, as well as key tracers of stellar populations and Galactic chemical evolution. However, standard spectroscopic abundance analyses can be prone to severe systematic errors, by the assumption that the stellar atmosphere is one-dimensional (1D) and hydrostatic, and by ignoring departures from local thermodynamic equilibrium (LTE). To address this, we carry out 3D non-LTE radiative transfer calculations for CI and OI, and 3D LTE radiative transfer calculations for FeII, across the stagger-grid of 3D hydrodynamic model atmospheres. The absolute 3D non-LTE versus 1D LTE abundance corrections can be as severe as ~0.3dex for CI lines in low-metallicity F dwarfs, and ~0.6dex for OI lines in high-metallicity F dwarfs. The 3D LTE versus 1D LTE abundance corrections for FeII lines are less severe, typically less than +0.15dex. We use the corrections in a re-analysis of carbon, oxygen, and iron in 187 F and G dwarfs in the Galactic disk and halo. Applying the differential 3D non-LTE corrections to 1D LTE abundances visibly reduces the scatter in the abundance plots. The thick disk and high- halo population rise in carbon and oxygen with decreasing metallicity, reaching a maximum of [C/Fe]~=0.2 and a plateau of [O/Fe]~=0.6 at [Fe/H]~=~1.0. The low- halo population is qualitatively similar, albeit offset towards lower metallicities and with larger scatter. Nevertheless, these populations overlap in the [C/O] versus [O/H] plane, decreasing to a plateau of [C/O]~=0.6 below [O/H]~=1.0. In the thin-disk, stars having confirmed planet detections tend to have higher values of C/O at given [O/H]; this potential signature of planet formation is only apparent after applying the abundance corrections to the 1D LTE results. Our grids of line-by-line abundance corrections are publicly available and can readily be used to improve the accuracy of spectroscopic analyses of late-type stars.
- ID:
- ivo://CDS.VizieR/J/MNRAS/452/637
- Title:
- Distance-limited sample of MYSOs
- Short Name:
- J/MNRAS/452/637
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We analyse C^18^O (J=3-2) data from a sample of 99 infrared (IR)-bright massive young stellar objects (MYSOs) and compact HII regions that were identified as potential molecular-outflow sources in the Red MSX Source survey. We extract a distance-limited (D<6kpc) sample shown to be representative of star formation covering the transition between the source types. At the spatial resolution probed, Larson-like relationships are found for these cores, though the alternative explanation, that Larson's relations arise where surface-density-limited samples are considered, is also consistent with our data. There are no significant differences found between source properties for the MYSOs and HII regions, suggesting that the core properties are established prior to the formation of massive stars, which subsequently have little impact at the later evolutionary stages investigated. There is a strong correlation between dust-continuum and C^18^O-gas masses, supporting the interpretation that both trace the same material in these IR-bright sources. A clear linear relationship is seen between the independently established core masses and luminosities. The position of MYSOs and compact HII regions in the mass-luminosity plane is consistent with the luminosity expected from the most massive protostar in the cluster when using an ~40 percent star formation efficiency and indicates that they are at a similar evolutionary stage, near the end of the accretion phase.
- ID:
- ivo://CDS.VizieR/J/ApJS/136/463
- Title:
- Distances and metallicities of HVCs and IVCs
- Short Name:
- J/ApJS/136/463
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A table is presented that summarizes published absorption line measurements for the high- and intermediate-velocity clouds (HVCs and IVCs). New values are derived for N(HI) in the direction of observed probes, in order to arrive at reliable abundances and abundance limits (the HI data are described in Paper II, Wakker et al., 2001ApJS..136..537W). Distances to stellar probes are revisited and calculated consistently, in order to derive distance brackets or limits for many of the clouds, taking care to properly interpret nondetections.
- ID:
- ivo://CDS.VizieR/J/ApJS/94/127
- Title:
- Distribution of H I in the ISM. I.
- Short Name:
- J/ApJS/94/127
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We compile, from the existing literature, the largest sample to date (842 data points) of hydrogen column density measurements, N(HI), of the gas in the interstellar medium. We include only results obtained from absorption measurements toward individual stars (594 in our sample) in an effort to construct a three-dimensional picture of the interstellar gas. We derive hydrogen column densities toward a fraction of the stars in the sample from published column density measurements of metal ions. A three-dimensional physical model derived from this data set will be presented in a companion paper. The observed stars span distances from a few parsecs to a few thousand parsecs, and more than half of the sample serves to describe the local interstellar medium within a few hundred parsecs of the Sun. Hydrogen column densities range from 10^17^ to 10^22^cm^-2^. We describe here the various observational methods used to estimate the hydrogen column densities and present the table with the stellar and hydrogen column density data. The provided table is intended as a global reference work, not to introduce new results.
- ID:
- ivo://CDS.VizieR/J/ApJ/899/166
- Title:
- Disturbance storm time index of 1903 sun outburst
- Short Name:
- J/ApJ/899/166
- Date:
- 14 Mar 2022 09:07:00
- Publisher:
- CDS
- Description:
- This paper presents the results of the spectrum analysis of the B-type magnetic chemically peculiar star HR465. HR465 shows unusual abundance patterns that vary with a period of 21.5yr. Our observations are recorded at ph=0.45, 0.68, and 0.85 of the spectroscopic period, where ph=0 represents the phase of maximum flux in the photometric y-band. Synthetic spectra, computed using an LTE atmosphere model, are fit to high-resolution ultraviolet Hubble Space Telescope (ph=0.45) spectra obtained as part of the Advanced Spectral Library Project: Hot Stars program. The ultraviolet data are supplemented by high-resolution optical spectra (ph=0.68 and 0.85) recorded at the Nordic Optical Telescope with the SOFIN spectrograph. The optical data are used as a complement to the high line-density ultraviolet spectrum to derive accurate abundances for elements without spectral lines in the ultraviolet and to improve the abundance phase coverage for many atoms/ions. This analysis presents abundance results for more than 70 atoms/ions and confirms parts of the abundance characteristics previously reported where elements with high mass numbers show significant abundance enhancements compared with solar values while some of the lighter elements show abundance deficiencies. In addition, our measured abundances are consistent with the periodic variability for chromium and rare-earth elements. Our results are compared with earlier investigations of this peculiar object to constrain stellar abundance and diffusion.
- ID:
- ivo://CDS.VizieR/J/A+A/611/A76
- Title:
- DLAS dust-corrected metallicity
- Short Name:
- J/A+A/611/A76
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Interpreting abundances of damped Ly-{alpha} absorbers (DLAs) from absorption-line spectroscopy has typically been a challenge because of the presence of dust. Nevertheless, because DLAs trace distant gas-rich galaxies regardless of their luminosity, they provide an attractive way of measuring the evolution of the metallicity of the neutral gas with cosmic time. This has been done extensively so far, but typically not taking proper dust corrections into account. The aims of this paper are to: (i) provide a simplified way of calculating dust corrections, based on a single observed [X/Fe], (ii) assess the importance of dust corrections for DLA metallicities and their evolution, and (iii) investigate the cosmic evolution of iron for a large DLA sample. We have derived dust corrections based on the observed [Zn/Fe], [Si/Fe], or [S/Fe], and confirmed their robustness. We present dust-corrected metallicities in a scale of [Fe/H]tot for 236 DLAs over a broad range of z, and assess the extent of dust corrections for different metals at different metallicities. Dust corrections in DLAs are important even for Zn (typically of 0.1-0.2, and up to 0.5dex), which is often neglected. Finally, we study the evolution of the dust-corrected metallicity with z. The DLA metallicities decrease with redshift, by a factor of 50-100 from today to ~12.6 billion years ago (z=5). When including dust corrections, the average DLA metallicities are 0.4-0.5dex higher than without corrections. The upper envelope of the relation between metallicity and z reaches solar metallicity at z<~0.5, although some systems can have solar metallicity already out to z~3.
- ID:
- ivo://CDS.VizieR/J/MNRAS/435/482
- Title:
- DLA system from SDSS DR5
- Short Name:
- J/MNRAS/435/482
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the chemical abundance measurements of the first large, medium-resolution, uniformly selected damped Lyman {alpha} system (DLA) survey. The sample contains 99 DLAs towards 89 quasars selected from the SDSS DR5 DLA sample in a uniform way. We analyse the metallicities and kinematic diagnostics, including the velocity width of 90 percent of the optical depth, {Delta}V_90_, and the equivalent widths of the SiII {lambda}1526 (W}{lambda}1526), CIV {lambda}1548 and MgII {lambda}2796 transitions. To avoid strong line-saturation effects on the metallicities measured in medium-resolution spectra (FWHM~71km/s), we derived metallicities from metal transitions which absorbed at most 35 percent of the quasar continuum flux. We find the evolution in cosmic mean metallicity of the sample, <Z>=(-0.04+/-0.13)z-(1.06+/-0.36), consistent with no evolution over the redshift range z~[2.2, 4.4], but note that the majority of our sample falls at z~[2.2, 3.5]. The apparent lack of metallicity evolution with redshift is also seen in a lack of evolution in the median {Delta}V_90_ and W{lambda}1526 values. While this result may seem to conflict with other large surveys that have detected significant metallicity evolution, such as Rafelski et al. who found <Z>=(-0.22+/-0.03)z-(0.65+/-0.09) over z~[0, 5], several tests show that these surveys are not inconsistent with our new result. However, over the smaller redshift range covered by our uniformly selected sample, the true evolution of the cosmic mean metallicity in DLAs may be somewhat flatter than the Rafelski et al. (2012ApJ...755...89R, Cat. J/ApJ/755/89) estimate.