- ID:
- ivo://CDS.VizieR/J/AJ/113/1073
- Title:
- Abundances in Cepheid Variables
- Short Name:
- J/AJ/113/1073
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have completed spectroscopic studies of 23 Galactic cepheids to determine possible metallicity effects on measuring the zero point of the P-L relation. We find a spread of 0.4dex in [Fe/H], which is not the result of either observational scatter or of a metallicity gradient within the Galactic disk. We find a smaller, less significant spread of 0.2dex in [{alpha}/Fe]. Our results are robust, determined by constancy of [Fe/H] derived at differing temperatures throughout the pulsational cycle, and abundances of two dwarfs compared to U Sgr in the cluster M25. We discuss briefly the effect of metallicity on the P-L relation. We also argue that EV Sct and QZ Nor are overtone pulsators, and that the latter is not a member of the cluster NGC 6067. (Copyright) 1997 American Astronomical Society.
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- ID:
- ivo://CDS.VizieR/J/ApJ/662/15
- Title:
- Abundances in extragalactic HII regions
- Short Name:
- J/ApJ/662/15
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We determine the primordial helium mass fraction Yp using 93 spectra of 86 low-metallicity extragalactic HII regions. This sample constitutes the largest and most homogeneous high-quality data set in existence for the determination of Yp. For comparison, and to improve the statistics in our investigation of systematic effects affecting the Yp determination, we have also considered a sample of 271 low-metallicity HII regions selected from Data Release 5 of the Sloan Digital Sky Survey. Although this larger sample shows more scatter, it gives results that are consistent at the 2{sigma} level with our original sample. We have considered known systematic effects that may affect the ^4^He abundance determination.
- ID:
- ivo://CDS.VizieR/J/A+A/571/A40
- Title:
- Abundances in 2 extremely metal-poor stars
- Short Name:
- J/A+A/571/A40
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- It has been noted that, in classical extremely metal-poor (EMP) stars, the abundance ratio of two well-observed neutroncapture elements, Sr and Ba, is always higher than [Sr/Ba]=-0.5, which is the value of the solar r-only process; however, a handful of EMP stars have recently been found with a very low Sr/Ba ratio. We try to understand the origin of this anomaly by comparing the abundance pattern of the elements in these stars and in the classical EMP stars. For a rigorous comparison with previous data, four stars with very low Sr/Ba ratios were observed and analyzed in the same way as in the First Stars Program: analysis within LTE approximation through 1D (hydrostatic) model atmosphere, providing homogeneous abundances of nine neutron-capture elements.
- ID:
- ivo://CDS.VizieR/J/ApJ/768/L12
- Title:
- Abundances in host stars XO-2S and XO-2N
- Short Name:
- J/ApJ/768/L12
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- With the aim of connecting the compositions of stars and planets, we present the abundances of carbon and oxygen, as well as iron and nickel, for the transiting exoplanet host star XO-2N and its wide-separation binary companion XO-2S. Stellar parameters are derived from high-resolution, high signal-to-noise spectra, and the two stars are found to be similar in their T_eff_, log g, iron ([Fe/H]), and nickel ([Ni/H]) abundances. Their carbon ([C/H]) and oxygen ([O/H]) abundances also overlap within errors, although XO-2N may be slightly more C-rich and O-rich than XO-2S. The C/O ratios of both stars (~0.60+/-0.20) may also be somewhat larger than solar (C/O~0.50). The XO-2 system has a transiting hot Jupiter orbiting one binary component but not the other, allowing us to probe the potential effects planet formation might have on the host star composition. Additionally, with multiple observations of its atmosphere the transiting exoplanet XO-2b lends itself to compositional analysis, which can be compared to the natal chemical environment established by our binary star elemental abundances. This work sets the stage for determining how similar or different exoplanet and host star compositions are, and the implications for planet formation, by discussing the C/O ratio measurements in the unique environment of a visual binary system with one star hosting a transiting hot Jupiter.
- ID:
- ivo://CDS.VizieR/J/ApJ/857/2
- Title:
- Abundances in 6 metal-poor stars
- Short Name:
- J/ApJ/857/2
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present new abundances derived from CuI, CuII, ZnI, and ZnII lines in six warm (5766<=T_eff_<=6427K), metal-poor (-2.50<=[Fe/H]<=-0.95) dwarf and subgiant (3.64<=logg<=4.44) stars. These abundances are derived from archival high-resolution ultraviolet spectra from the Space Telescope Imaging Spectrograph on board the Hubble Space Telescope and ground-based optical spectra from several observatories. Ionized Cu and Zn are the majority species, and abundances derived from CuII and ZnII lines should be largely insensitive to departures from local thermodynamic equilibrium (LTE). We find good agreement between the [Zn/H] ratios derived separately from ZnI and ZnII lines, suggesting that departures from LTE are, at most, minimal (<~0.1dex). We find that the [Cu/H] ratios derived from CuII lines are 0.36+/-0.06dex larger than those derived from CuI lines in the most metal-poor stars ([Fe/H]{<}-1.8), suggesting that LTE underestimates the Cu abundance derived from CuI lines. The deviations decrease in more metal-rich stars. Our results validate previous theoretical non-LTE calculations for both Cu and Zn, supporting earlier conclusions that the enhancement of [Zn/Fe] in metal-poor stars is legitimate, and the deficiency of [Cu/Fe] in metal-poor stars may not be as large as previously thought.
- ID:
- ivo://CDS.VizieR/J/A+A/579/A104
- Title:
- Abundances in NGC 5053 and NGC 5634
- Short Name:
- J/A+A/579/A104
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The tidal disruption of the Sagittarius dwarf Spheroidal galaxy (Sgr dSph) is producing the most prominent substructure in the Milky Way (MW) halo, the Sagittarius Stream. Aside from field stars, the Sgr dSph is suspected to have lost a number of globular clusters (GC). Many Galactic GC are suspected to have originated in the Sgr dSph. While for some candidates an origin in the Sgr dSph has been confirmed due to chemical similarities, others exist whose chemical composition has never been investigated. NGC 5053 and NGC 5634 are two among these scarcely studied Sgr dSph candidate-member clusters. To characterize their composition we analyzed one giant star in NGC 5053, and two in NGC 5634. We analize high-resolution and signal-to-noise spectra by means of the MyGIsFOS code, determining atmospheric parameters and abundances for up to 21 species between O and Eu. The abundances are compared with those of MW halo field stars, of "unassociated" MW halo globulars, and of the metal poor Sgr dSph main body population. We derive a metallicity of [FeII/H]=-2.26+/-0.10 for NGC 5053, and of [FeI/H]=-1.99+/-0.075 and -1.97+/-0.076 for the two stars in NGC 5634. This makes NGC 5053 one of the most metal poor globular clusters in the MW. Both clusters display an alpha enhancement similar to the one of the halo at comparable metallicity. The two stars in NGC 5634 clearly display the Na-O anticorrelation widespread among MW globulars. Most other abundances are in good agreement with standard MW halo trends. The chemistry of the Sgr dSph main body populations is similar to the one of the halo at low metallicity. It is thus difficult to discriminate between an origin of NGC 5053 and NGC 5634 in the Sgr dSph, and one in the MW. However, the abundances of these clusters do appear closer to that of Sgr dSph than of the halo, favoring an origin in the Sgr dSph system.
- ID:
- ivo://CDS.VizieR/J/ApJ/682/1029
- Title:
- Abundances in OGLE-2007-BLG-349S
- Short Name:
- J/ApJ/682/1029
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present an abundance analysis based on high-dispersion and high signal-to-noise ratio Keck spectra of a very highly microlensed Galactic bulge dwarf, OGLE-2007-BLG-349S, with Teff~5400K. The amplification at the time the spectra were taken ranged from 350 to 450. This bulge star is highly enhanced in metallicity with [Fe/H]=+0.51+/-0.09dex. The abundance ratios for the 28 species of 26 elements for which features could be detected in the spectra are almost all solar. In particular, there is no evidence for enhancement of any of the {alpha}-elements, including O and Mg. We conclude that the high [Fe/H] seen in this star, when combined with the equally high [Fe/H] derived in previous detailed abundance analysis of two other Galactic bulge dwarfs, both also highly magnified by microlensing, implies that the median metallicity in the Galactic bulge is very high. We thus infer that many previous estimates of the metallicity distribution in the Galactic bulge have substantially underestimated the mean Fe metallicity there due to sample bias, and suggest a candidate mechanism for such. If our conjecture proves valid, it may be necessary to update the calibrations for the algorithms used by many groups to interpret spectra and broadband photometry of the integrated light of very metal-rich old stellar populations, including luminous elliptical galaxies.
- ID:
- ivo://CDS.VizieR/J/ApJ/824/75
- Title:
- Abundances in 23 open clusters. I.
- Short Name:
- J/ApJ/824/75
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Neutron-capture elements, those with Z>35, are the least well understood in terms of nucleosynthesis and formation environments. The rapid neutron-capture, or r-process, elements are formed in the environments and/or remnants of massive stars, while the slow neutron-capture, or s-process, elements are primarily formed in low-mass AGB stars. These elements can provide much information about Galactic star formation and enrichment, but observational data are limited. We have assembled a sample of 68 stars in 23 open clusters that we use to probe abundance trends for six neutron-capture elements (Eu, Gd, Dy, Mo, Pr, and Nd) with cluster age and location in the disk of the Galaxy. In order to keep our analysis as homogeneous as possible, we use an automated synthesis fitting program, which also enables us to measure multiple (3-10) lines for each element. We find that the pure r-process elements (Eu, Gd, and Dy) have positive trends with increasing cluster age, while the mixed r- and s-process elements (Mo, Pr, and Nd) have insignificant trends consistent with zero. Pr, Nd, Eu, Gd, and Dy have similar, slight (although mostly statistically significant) gradients of ~0.04dex/kpc. The mixed elements also appear to have nonlinear relationships with R_GC_.
- ID:
- ivo://CDS.VizieR/J/A+A/572/A82
- Title:
- Abundances in outer parts of Fornax dSph
- Short Name:
- J/A+A/572/A82
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present radial velocities and [Fe/H] abundances for 340 stars in the Fornax dwarf spheroidal from R~16000 spectra. The targets were obtained in the outer parts of the galaxy. Our sample shows a wide range in [Fe/H], between -0.5 and -3.0dex, in which we detect three subgroups. Removal of stars belonging to the most metal-rich population produces a truncated metallicity distribution function that is identical to Sculptor, indicating that these systems shared a similar early evolution. The derived age-metallicity relation shows a fast increase in [Fe/H] at early ages, after which the enrichment flattens significantly for stars younger than ~8Gyr. Additionally, the data indicate a strong population of stars around 4Gyr, followed by a second rapid enrichment in [Fe/H]. Our dynamical analysis reveals an increasing velocity dispersion with decreasing [Fe/H] from sigma_sys_=7.5km/s to 14km/s. The large velocity dispersion at low metallicities is possibly the result of a non-Gaussian velocity distribution among stars older than ~8Gyr. Our sample also includes members from the Fornax globular clusters H2 and H5. In agreement with past studies we find [Fe/H]=-2.04+/-0.04 and a mean radial velocity RV=59.36+/-0.31km/s for H2 and [Fe/H]=-2.02+/-0.11 and RV=59.39+/-0.44km/s for H5. Overall, we find high complexity in the chemical and dynamical properties, with signatures that additionally vary with galactocentric distance.
- ID:
- ivo://CDS.VizieR/J/AJ/110/2319
- Title:
- Abundances in RR Lyr variables
- Short Name:
- J/AJ/110/2319
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have used moderately high-resolution, high S/N spectra to study the chemical composition of ten field ab-type RR Lyrae stars. Variables having accurate photometric and radial-velocity data were selected, in order to derive a precise estimate of the atmospheric parameters independently of excitation and ionization equilibria. A new temperature scale was determined from literature "Infrared Flux Method" measures of subdwarfs and the Kurucz (1992) (priv. com.) model atmospheres, and used to calibrate colors for both dwarfs and RR Lyraes. Photometric reddening estimates for the program stars were carefully examined, and compared with other determinations. The applicability of Kurucz (1992) (priv. com.) model atmospheres in the analysis of RR Lyraes at minimum light was analyzed: we found that they are able to reproduce colors, excitation, and ionization equilibria as well as the wings of Halpha. The comparison solar abundances were carefully determined. From a new analysis of weak Fe I lines with accurate gfs [Bard & Kock, A&A, 282, 1014 (1994)] we derived log epsilon(Fe)_Sun=7.52, in agreement with the Fe abundances determined from meteorites and Fe II lines. We derived abundances for 21 species. Main results are: The metal abundances of the program stars span the range -2.50<[Fe/H]<+0.17. Lines of most elements are found to form in LTE conditions. Fe lines satisfy very well the excitation and ionization equilibria. A comparison with statistical equilibrium computations shows that rather large collisional cross sections are required to reproduce observations. If these cross sections are then used in the analysis of the formation of Fe lines in subdwarfs and RGB stars, no significant departures from LTE are found for these stars, thus validating the very numerous LTE analyses. RR Lyraes share the typical abundance pattern of other stars of similar [Fe/H]: alpha-elements are overabundant by ~0.4dex and Mn is underabundant by ~0.6dex in stars with [Fe/H]<-1. Solar scaled abundances are found for most of the other species, except for the low Ba abundance in the extremely metal-poor star X Ari ([Fe/H]~-2.5). Significant departures from LTE are found for a few species: Nd II, Ce II, Y II, and Sc II are severely underabundant (~0.5dex) in metal-rich variables; Ti I and Cr I are slightly (~0.1-0.2dex) underabundant in metal-poor stars. These effects are attributed to overionization. We suggest that the photoionization of the alkaline earth-like ions is due to Lyman lines emission produced by the shock waves that propagate in the atmosphere of these variables [Fokin (1992MNRAS.256...26F)]. Departures from LTE were considered in detail in the derivation of abundances for the light elements (O and Na). Significant corrections were required for the O I IR triplet and the Na D lines. The resulting pattern reproduces that observed in less evolved field stars. We did not find any evidence for an O-Na anticorrelation among these field HB stars, suggesting that the environment is likely to be responsible for the anticorrelation found in metal-poor globular cluster stars [Sneden et al. =1992AJ....104.2121S]. We used our new [Fe/H] abundances, as well as values from Butler and co-workers (corrected to our system), and from high- resolution spectroscopy of globular clusters giants, to obtain a revised calibration of the low-resolution metallicity index Delta(S) [Preston =1959ApJ...130..507P]: [Fe/H]=-0.194(+/-0.011)Delta(S)-0.08(+/-0.18). Our new metallicity scale is stretched on both low and high metallicity ends with respect to Butler's [1975ApJ...200...68B]. The error in [Fe/H] by Delta(S) observations is 0.16dex, well of the same order of high-resolution metallicity determinations. The slope of the calibration obtained considering only stars with 4<Delta(S)<10 is slightly smaller than that obtained using all stars. While this difference is only barely significant, it might point out the presence of a nonlinearity of the Delta(S) vs [Fe/H] relation, as suggested by Manduca [ApJ, 245, 258 (1981)]. The new [Fe/H] values were used to update the metallicity calibration of the Ca II K line index [Clementini et al. =1991AJ....101.2168C]. Using the present new metallicities, and W'(K) values and relative errors from Clementini et al. (1991), a least-squares fit weighted both in W'(K) and [Fe/H] gives [Fe/H]=0.65(+/-0.17)W'(K)-3.49(+/-0.39). Finally, our new metallicity scale was used to revise the metallicity dependence of the absolute magnitude of RR Lyrae stars, M_V. Using M_V values from Fernley [1994A&A...284L..16F] for the field stars, and estimates from Liu & Janes [1990ApJ...360..561L] and Storm et al. [1994A&A...290..443S] for the cluster variables, we found M_V=0.20(+/-0.03) [Fe/H]+1.06(+/-0.04) and M_V=0.19(+/-0.03)[Fe/H]+0.96(+/-0.04), the last being obtained by using M_V estimates derived for a value of the conversion factor between observed and true pulsation velocity p=1.38 (Fernley 1994). The adoption of the new metallicity scale does not yield significant changes in the slope or zero point of the M_V vs [Fe/H] relation. Observations do not rule out the possibility that the slope of the M_V vs [Fe/H] relation might be different for metal-poor and metal-rich variables. However, a larger sample of Baade-Wesselink M_V determinations is required to definitely settle this question.
