We present the detection of 10 lines of singly ionized neodymium (Nd ii, Z = 60) in H-band spectra using observations from the SDSS-III Apache Point Observatory Galactic Evolution Experiment (APOGEE) survey. These lines were detected in a metal-poor ([Fe/H] ∼ −1.5), neutron-capture element-enhanced star recently discovered in the APOGEE sample. Using an optical high-resolution spectrum, we derive a Nd abundance for this star using Nd ii lines with precise, laboratory-derived gf values. This optical abundance is used to derive log(gf) values for the H-band lines. We use these lines to rederive Nd ii abundances for two more metal-rich, s-process enhanced stars observed by APOGEE and find that these lines yield consistent Nd ii abundances, confirming the Nd enhancement of these stars. We explore the region of parameter space in the APOGEE sample over which these lines can be used to measure Nd ii abundances. We find that Nd abundances can be reliably derived for ∼18% of the red giants observed by APOGEE. This will result in ∼50,000 Milky Way stars with Nd ii abundances following the conclusion of APOGEE-2, allowing for studies of neutron-capture element abundance distributions across the entire Milky Way.

In this paper, we present an homogeneous analysis of photospheric abundances based on high-resolution spectroscopy of a sample of 182 barium stars and candidates. We determined atmospheric parameters, spectroscopic distances, stellar masses, ages, luminosities and scaleheight, radial velocities, abundances of the Na, Al, α-elements, iron-peak elements, and s-process elements Y, Zr, La, Ce, and Nd. We employed the local thermodynamic equilibrium model atmospheres of Kurucz and the spectral analysis code moog. We found that the metallicities, the temperatures and the surface gravities for barium stars cannot be represented by a single Gaussian distribution. The abundances of α-elements and iron peak elements are similar to those of field giants with the same metallicity. Sodium presents some degree of enrichment in more evolved stars that could be attributed to the NeNa cycle. As expected, the barium stars show overabundance of the elements created by the s-process. By measuring the mean heavy-element abundance pattern as given by the ratio [s/Fe], we found that the barium stars present several degrees of enrichment. We also obtained the [hs/ls] ratio by measuring the photospheric abundances of the Ba-peak and the Zr-peak elements. Our results indicated that the [s/Fe] and the [hs/ls] ratios are strongly anticorrelated with the metallicity. Our kinematical analysis showed that 90 per cent of the barium stars belong to the thin disc population. Based on their luminosities, none of the barium stars are luminous enough to be an asymptotic giant branch star, nor to become self-enriched in the s-process elements. Finally, we determined that the barium stars also follow an age–metallicity relation.

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New elemental abundances for the neutron-capture elements Sr, Nb, Mo, Ru, La, Sm, and Eu are presented for a large sample of 180 barium (Ba) giant stars, a class of chemically peculiar objects that exhibit in their spectra enhancements of the elements created by the s-process, as a consequence of mass transfer between the components of a binary system. The content of heavy elements in these stars, in fact, points to nucleosynthesis mechanisms that took place within a former asymptotic giant branch (AGB) companion, now an invisible white dwarf. From high-resolution (⁠|$R=48\, 000$|⁠) spectra in the optical, we derived the abundances either by equivalent width measurements or synthetic spectra computations, and compared them with available data for field giant and dwarf stars in the same range of metallicity. A re-determination of La abundances resulted in [La/Fe] ratios up to 1.2 dex lower than values previously reported in literature. The programme Ba stars show overabundance of neutron-capture elements, except for Eu, for which the observational data set behave similarly to field stars. Comparison to model predictions are satisfactory for second-to-first s-process peak ratios (e.g. [La/Sr]) and the ratios of the predominantly r-process element Eu to La. However, the observed [Nb, Mo, Ru/Sr] and [Ce, Nd, Sm/La] ratios show median values higher or at the upper limits of the ranges of the model predictions. This unexplained feature calls for new neutron capture models to be investigated.

Context. Open clusters are very useful targets for examining possible trends in galactocentric distance and age, especially when young and old open clusters are compared. Aims. We carried out a detailed spectroscopic analysis to derive the chemical composition of seven red giants in the young open cluster NGC 3114. Abundances of C, N, O, Li, Na, Mg, Al, Ca, Si, Ti, Ni, Cr, Y, Zr, La, Ce, and Nd were obtained, as well as the carbon isotopic ratio. Methods. The atmospheric parameters of the studied stars and their chemical abundances were determined using high-resolution optical spectroscopy. We employed the local-thermodynamic-equilibrium model atmospheres of Kurucz and the spectral analysis code MOOG. The abundances of the light elements were derived using the spectral synthesis technique. Results. We found that NGC 3114 has a mean metallicity of [Fe/H] = −0.01 ± 0.03. The isochrone fit yielded a turn-off mass of 4.2 M_⊙. The [N/C] ratio is in good agreement with the models predicted by first dredge-up. We found that two stars, HD 87479 and HD 304864, have high rotational velocities of 15.0 km s^-1 and 11.0 km s^-1; HD 87526 is a halo star and is not a member of NGC 3114. Conclusions. The carbon and nitrogen abundance in NGC 3114 agree with the field and cluster giants. The oxygen abundance in NGC 3114 is lower compared to the field giants. The [O/Fe] ratio is similar to the giants in young clusters. We detected sodium enrichment in the analyzed cluster giants. As far as the other elements are concerned, their [X/Fe] ratios follow the same trend seen in giants with the same metallicity.

We report on the analysis of high-resolution optical spectra of the yellow component of the symbiotic star He2-467. The chemical composition of its atmosphere reveals He2-467 to be a metal-poor K giant with [Fe/H] = -1.1. From a set of 14 Fe I lines, its radial velocity is found to be -106.9 ± 0.5 km s^-1. This high velocity plus low metallicity points to He2-467 being a halo star. The K giant in He2-467 is also enriched in the heavy s-process elements. Because its luminosity is below that for an asymptotic giant branch (AGB) star that could have commenced shell helium-burning (via thermal pulses) and become self-enriched in the neutron-capture elements, we ascribe its heavy-element excess to the barium star phenomenon. In this scenario, the secondary component accreted matter from the primary (now the white dwarf) when it was a thermally pulsing AGB star overabundant in s-process elements. The heavy-element abundance distribution of He2-467, as well as its atmospheric parameters, is almost identical to two yellow symbiotics analyzed previously, AG Dra and BD -21°3873. In particular, its neutron exposure parameter, τ, which characterizes the s-process abundance distribution, is larger than for solar metallicities (with a single-exposure τ = 1.1 millibarn^-1). Also, analysis of the rubidium abundance in He2-467 reveals that the s-process ratio of N(Rb)/N(Zr) is much larger than for solar metallicity s-process material, indicating that the s-process neutron density is considerably larger at lower metallicities, in agreement with the ¹³C(α, n)¹⁶O neutron source.