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Register a new userChemical abundance analysis of symbiotic giants. RW Hya, SY Mus, BX Mon, and AE Ara
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Symbiotic stars are the long period, binary systems of strongly interacting stars at the final stages of evolution which can be useful tool to understand the chemical evolution of the Galaxy and the formation of stellar populations. Knowledge of the chemical composition of the symbiotic giants is essential to advancing our understanding of these issues but unfortunately reliably determinations exist only in a few cases. We perform a program for detailed chemical composition analysis in over 30 symbiotic giants, based on the high resolution, near-IR spectra, obtained with Phoenix/Gemini South spectrometer. The methods of the standard LTE analysis is used to obtain photospheric abundances of CNO and elements around iron peak. Here we present results obtained for four objects: RW Hya, SY Mus, BX Mon, and AE Ara. Our analysis revealed a significantly sub-solar metallicity (Me/H ~ -0.75) for RW Hya, a slightly sub-solar metallicities (Me/H ~ 0.2-0.3) in BX Mon and AE Ara, and a near-solar metallicity in SY Mus. 12C/13C isotopic ratios are low in all cases, ranging from ~6 to ~10, and indicate that the giants have experienced the first dredge-up.
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The study of symbiotic systems is of considerable importance in our understanding of binary system stellar evolution in systems where mass loss or transfer takes place. Elemental abundances are of special significance since they can be used to track mass exchange. However, there are few symbiotic giants for which the abundances are fairly well determined. Here we present for the first time a detailed analysis of the chemical composition for the giants in the RW Hya and SY Mus systems. The analysis is based on high resolution (R 50000), high S/N, near-IR spectra. Spectrum synthesis employing standard LTE analysis and atmosphere models was used to obtain photospheric abundances of CNO and elements around the iron peak (Sc, Ti, Fe, and Ni). Our analysis reveals a significantly sub-solar metallicity, [Fe/H]-0.75}, for the RW Hya giant confirming its membership in the Galactic halo population and a near-solar metallicity for the SY Mus giant. The very low 12C/13C isotopic ratios, 6-10, derived for both objects indicate that the giants have experienced the first dredge-up
Knowledge of the elemental abundances of symbiotic giants is essential to address the role of chemical composition in the evolution of symbiotic binaries, to map their parent population, and to trace their mass transfer history. However, there are few symbiotic giants for which the photospheric abundances are fairly well determined. This is the second in a series of papers on chemical composition of symbiotic giants determined from high-resolution (R ~ 50000) near-IR spectra. Results are presented for the late-type giant star in the AE Ara, BX Mon, KX TrA, and CL Sco systems. Spectrum synthesis employing standard local thermal equilibrium (LTE) analysis and stellar atmosphere models were used to obtain photospheric abundances of CNO and elements around the iron peak (Sc, Ti, Fe, and Ni). Our analysis resulted in sub-solar metallicities in BX Mon, KX TrA, and CL Sco by [Fe/H] ~ -0.3 or -0.5 depending on the value of microturbulence. AE Ara shows metallicity closer to solar by ~0.2 dex. The enrichment in 14N isotope found in all these objects indicates that the giants have experienced the first dredge-up. In the case of BX Mon first dredge-up is also confirmed by the low 12C/13C isotopic ratio of ~8.
Symbiotic stars (SySt) are binaries composed of a star in the later stages of evolution and a stellar remnant. The enhanced mass-loss from the giant drives interacting mass exchange and makes these systems laboratories for understanding binary evolution. Studies of the chemical compositions are particularly useful since this parameter has strong impact on the evolutionary path. The previous paper in this series presented photospheric abundances for 24 giants in S-type SySt enabling a first statistical analysis. Here we present results for an additional sample of 13 giants. The aims are to improve statistics of chemical composition involved in the evolution of SySt, to study evolutionary status, mass transfer and to interpret this in terms of Galactic populations. High-resolution, near-IR spectra are used, employing the spectrum synthesis method in a classical approach, to obtain abundances of CNO and elements around the iron peak (Fe, Ti, Ni). Low-resolution spectra in the region around the Ca II triplet were used for spectral classification. The metallicities obtained cover a wide range with a maximum around ~-0.2 dex. The enrichment in the 14N isotope indicates that these giants have experienced the first dredge-up. Relative O and Fe abundances indicate that most SySt belong to the Galactic disc; however, in a few cases, the extended thick-disc/halo is suggested. Difficult to explain, relatively high Ti abundances can indicate that adopted microturbulent velocities were too small by ~0.2-0.3 km/s. The revised spectral types for V2905 Sgr, and WRAY 17-89 are M3 and M6.5, respectively.
We aim at deriving accurate atmospheric parameters and chemical abundances of 19 barium (Ba) stars, including both strong and mild Ba stars, based on the high signal-to-noise ratio and high resolution Echelle spectra obtained from the 2.16 m telescope at Xinglong station of National Astronomical Observatories, Chinese Academy of Sciences. The chemical abundances of the sample stars were obtained from an LTE, plane-parallel and line-blanketed atmospheric model by inputting the atmospheric parameters (effective temperatures, surface gravities, metallicity and microturbulent velocity) and equivalent widths of stellar absorption lines. These samples of Ba stars are giants indicated by atmospheric parameters, metallicities and kinematic analysis about UVW velocity. Chemical abundances of 17 elements were obtained for these Ba stars. Their light elements (O, Na, Mg, Al, Si, Ca, Sc, Ti, V, Cr, Mn and Ni) are similar to the solar abundances. Our samples of Ba stars show obvious overabundances of neutron-capture (n-capture) process elements relative to the Sun. Their median abundances of [Ba/Fe], [La/Fe] and [Eu/Fe] are 0.54, 0.65 and 0.40, respectively. The YI and ZrI abundances are lower than Ba, La and Eu, but higher than the light elements for the strong Ba stars and similar to the iron-peak elements for the mild stars. There exists a positive correlation between Ba intensity and [Ba/Fe]. For the n-capture elements (Y, Zr, Ba, La), there is an anti-correlation between their [X/Fe] and [Fe/H]. We identify nine of our sample stars as strong Ba stars with [Ba/Fe]>0.6 where seven of them have Ba intensity Ba=2-5, one has Ba=1.5 and another one has Ba=1.0. The remaining ten stars are classified as mild Ba stars with 0.17<[Ba/Fe]<0.54.
The elemental abundance structure of the Galactic disc has been extensively studied in the solar neighbourhood using long-lived stars such as F and G dwarfs or K and M giants. These are stars whose atmospheres preserve the chemical composition of their natal gas clouds, and are hence excellent tracers of the chemical evolution of the Galaxy. As far as we are aware, there are no such studies of the inner Galactic disc, which hampers our ability to constrain and trace the origin and evolution of the Milky Way. Therefore, we aim in this study to establish the elemental abundance trend(s) of the disc(s) in the inner regions of the Galaxy. Based on equivalent width measurements in high-resolution spectra obtained with the MIKE spectrograph on the Magellan II telescope on Las Campanas in Chile, we determine elemental abundances for 44 K-type red giant stars in the inner Galactic disc, located at Galactocentric distances of 4-7,kpc. The analysis method is identical to the one recently used on red giant stars in the Galactic bulge and in the nearby thin and thick discs, enabling us to perform a truly differential comparison of the different stellar populations. We present the first detailed elemental abundance study of a significant number of red giant stars in the inner Galactic disc. We find that these inner disc stars show the same type of chemical and kinematical dichotomy as the thin and thick discs show in the solar neighbourhood. The abundance trends of the inner disc agree very well with those of the nearby thick disc, and also to those of the Bulge. The chemical similarities between the Bulge and the Galactic thick disc stellar populations indicate that they have similar chemical histories, and any model trying to understand the formation and evolution of either of the two should preferably incorporate both of them.
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