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Register a new userThe RRC Stars: Chemical Abundances and Envelope Kinematics
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We analyzed series of spectra obtained for twelve stable RRc stars observed with the echelle spectro- graph of the du Pont telescope at Las Campanas Observatory and we analyzed the spectra of RRc Blazhko stars discussed by Govea et al. (2014). We derived model atmosphere parameters, [Fe/H] metallicities, and [X/Fe] abundance ratios for 12 species of 9 elements. We co-added all spectra ob- tained during the pulsation cycles to increase S/N and demonstrate that these spectra give results superior to those obtained by co-addition in small phase intervals. The RRc abundances are in good agreement with those derived for the RRab stars of Chadid et al. (2017). We used radial velocity measurements of metal lines and H{alpha} to construct variations of velocity with phase, and center-of-mass velocities. We used these to construct radial-velocity templates for use in low-medium resolution radial velocity surveys of RRc stars. Additionally, we calculated primary accelerations, radius variations, metal and H{alpha} velocity amplitudes, which we display as regressions against primary acceleration. We employ these results to compare the atmosphere structures of metal-poor RRc stars with their RRab counterparts. Finally, we use the radial velocity data for our Blazhko stars and the Blazhko periods of Szczygie l & Fabrycky (2007) to falsify the Blazhko oblique rotator hypothesis.
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We perform a detailed elemental abundance study of the early-type B star HD 28248 and estimate its orbital path in the Galaxy. From the comparison of spectroscopic observations performed at the European Southern Observatory at La Silla in 2001/Oct/07 with non-LTE synthetic spectra using a new wrapper for the simultaneous fitting of several lines of a given atomic species, the abundances of He, C, N, O, Mg, Al, Si, P, S, Ar and Fe were determined for the first time. The radial velocity of HD 28248 has been also estimated from the positions of centroids of nine neutral helium lines and Mg ii 4481 A, allowing to calculate its right-handed Galactic space-velocity components U, V and W and estimate its orbital path in the Galaxy for the first time. Our chemical analysis depicted an outstanding enrichment of several atomic species, particularly [Fe/H] = +0.25 dex and [O/Fe] = +0.32 dex. The kinematic parameters show that its orbit is confined to the galactic disk with a scale height of 400 pc and the star has moved about 4 kpc from its birthplace to the current position. The elemental abundances do not follow the predicted [Fe/H] and [O/Fe] gradients currently established for the Galaxy. A hypothetical scenario for the contamination could be the mass transfer in a binary system during previous evolutionary phases.
We have analysed a sample of 18 RR Lyrae stars (17 fundamental-mode - RRab - and one first overtone - RRc) and three Population II Cepheids (two BL Her stars and one W Vir star), for which high-resolution (R $ge$30000), high signal-to-noise (S/N$ge$30) spectra were obtained with either SARG at the Telescopio Nazionale Galileo (La Palma, Spain) or UVES at the ESO Very Large Telescope (Paranal, Chile). Archival data were also analyzed for a few stars, sampling $gtrsim$3 phases for each star. We obtained atmospheric parameters (T$_{rm{eff}}$, log$g$, v$_{rm{t}}$, and [M/H]) and abundances of several iron-peak and $alpha$-elements (Fe, Cr, Ni, Mg, Ca, Si, and Ti) for different pulsational phases, obtaining $<$[$alpha$/Fe]$>$=+0.31$pm$0.19 dex over the entire sample covering -2.2$<$[Fe/H]$<$-1.1 dex. We find that silicon is indeed extremely sensitive to the phase, as reported by previous authors, and cannot be reliably determined. Apart from this, metallicities and abundance ratios are consistently determined, regardless of the phase, within 0.10-0.15 dex, although caution should be used in the range $0lesssimphilesssim0.15$. Our results agree with literature determinations for both variable and non-variable field stars, obtained with very different methods, including low and high-resolution spectroscopy. W Vir and BL Her stars, at least in the sampled phases, appear indistinguishable from RRab from the spectroscopic analysis point of view. Our large sample, covering all pulsation phases, confirms that chemical abundances can be obtained for RR Lyrae with the classical EW-based technique and static model atmospheres, even rather close to the shock phases.
Results from high-resolution spectral analyses of a selected sample of CH stars are presented. Detailed chemical composition studies of these objects, which could reveal abundance patterns that in turn provide information regarding nucleosynthesis and evolutionary status, are scarce in the literature. We conducted detailed chemical composition studies for these objects based on high resolution (R ~ 42000) spectra. The spectra were taken from the ELODIE archive and cover the wavelength range from 3900 to 6800 A, in the wavelength range. We estimated the stellar atmospheric parameters, the effective temperature Teff, the surface gravity log g, and metallicity [Fe/H] from Local thermodynamic equilibrium analyses using model atmospheres. Estimated temperatures of these objects cover a wide range from 4550 K to 6030 K, the surface gravity from 1.8 to 3.8 and metallicity from -0.18 to -1.4. We report updates on elemental abundances for several heavy elements and present estimates of abundance ratios of Sr, Y, Zr, Ba, La, Ce, Pr, Nd, Sm, Eu and Dy with respect to Fe. For the object HD 188650 we present the first abundance analyses results based on a high resolution spectrum. Enhancements of heavy elements relative to Fe, that are characteristic of CH stars are evident from our analyses for most of the objects. A parametric model based study is performed to understand the relative contributions from the s- and r-processes to the abundances of the heavy elements.
The analysis of 20 years of spectrophotometric data of the double shell planetary nebula PM,1-188 is presented, aiming to determine the time evolution of the emission lines and the physical conditions of the nebula, as a consequence of the systematic fading of its [WC,10] central star whose brightness has declined by about 10 mag in the past 40 years. Our main results include that the [ion{O}{iii}], [ion{O}{ii}], [ion{N}{ii}] line intensities are increasing with time in the inner nebula as a consequence of an increase in electron temperature from 11,000 K in 2005 to more than 14,000 K in 2018, due to shocks. The intensity of the same lines are decreasing in the outer nebula, due to a decrease in temperature, from 13,000 K to 7,000 K, in the same period. The chemical composition of the inner and outer shells was derived and they are similar. Both nebulae present subsolar O, S and Ar abundances, while they are He, N and Ne rich. For the outer nebula the values are 12+log He/H= 11.13$pm$0.05, 12+log O/H = 8.04$pm$0.04, 12+log N/H= 7.87$pm$0.06, 12+log S/H = 7.18$pm$0.10 and 12+log Ar = 5.33$pm$0.16. The O, S and Ar abundances are several times lower than the average values found in disc non-Type I PNe, and are reminiscent of some halo PNe. From high resolution spectra, an outflow in the N-S direction was found in the inner zone. Position-velocity diagrams show that the outflow expands at velocities in the $-$150 to 100 km s$^{-1}$ range, and both shells have expansion velocities of about 40 km s$^{-1}$.
We present non-LTE oxygen abundances for a sample of B stars in the Orion association. The abundance calculations included non-LTE line formation and used fully blanketed non-LTE model atmospheres. The stellar parameters were the same as adopted in the previous study by Cunha & Lambert (1994). We find that the young Orion stars in this sample of 10 stars are described by a single oxygen abundance with an average value of A(O)=8.78 and a small dispersion of +/- 0.05 dex, which is of the order of the uncertainties in the analysis. This average oxygen abundance compares well with the average oxygen abundance obtained previously in Cunha & Lambert (1994): A(O) = 8.72 +/- 0.13 although this earlier study, based upon non-blanketed model atmospheres in LTE, displayed larger scatter. Small scatter of chemical abundances in Orion B stars had also been found in our previous studies for neon and argon; all based on the same effective temperature scale. The derived oxygen abundance distribution for the Orion association compares well with other results for the oxygen abundance in the solar neighborhood.
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