scholarly journals Abundance of zinc in the red giants of Galactic globular cluster 47 Tucanae

2018 ◽  
Vol 616 ◽  
pp. A142 ◽  
Author(s):  
A. Černiauskas ◽  
A. Kučinskas ◽  
J. Klevas ◽  
P. Bonifacio ◽  
H.-G. Ludwig ◽  
...  
Keyword(s):  
Globular Cluster ◽  
Abundance Ratio ◽  
Stellar Model ◽  
Local Thermal Equilibrium ◽  
Cluster Center ◽  
Red Giants ◽  
Light Elements ◽  
Individual Stars ◽  
Fitting Procedure ◽  
Red Giant

Aims. We investigate possible relations between the abundances of zinc and the light elements sodium, magnesium, and potassium in the atmospheres of red giant branch (RGB) stars of the Galactic globular cluster 47 Tuc and study connections between the chemical composition and dynamical properties of the cluster RGB stars. Methods. The abundance of zinc was determined in 27 RGB stars of 47 Tuc using 1D local thermal equilibrium (LTE) synthetic line profile fitting to the high-resolution 2dF/HERMES spectra obtained with the Anglo-Australian Telescope (AAT). Synthetic spectra used in the fitting procedure were computed with the SYNTHE code and 1D ATLAS9 stellar model atmospheres. Results. The average 1D LTE zinc-to-iron abundance ratio and its RMS variations due to star-to-star abundance spread determined in the sample of 27 RGB stars is 〈[Zn/Fe]〉1D LTE = 0.11 ± 0.09. We did not detect any statistically significant relations between the abundances of zinc and those of light elements. Neither did we find any significant correlation or anticorrelation between the zinc abundance in individual stars and their projected distance from the cluster center. Finally, no statistically significant relation between the absolute radial velocities of individual stars and the abundance of zinc in their atmospheres was detected. The obtained average [Zn/Fe]1DLTE ratio agrees well with those determined in this cluster in earlier studies and nearly coincides with that of Galactic field stars at this metallicity. All these results suggest that nucleosynthesis of zinc and light elements proceeded in separate, unrelated pathways in 47 Tuc.

scholarly journals Abundance of zirconium in the atmospheres of red giants in Galactic globular cluster 47 Tuc

2019 ◽  
Vol 14 (S351) ◽  
pp. 309-311
Author(s):  
Edgaras Kolomiecas ◽  
Vidas Dobrovolskas ◽  
Arūnas Kučinskas
Keyword(s):  
Globular Cluster ◽  
Globular Clusters ◽  
Stellar Model ◽  
Red Giants ◽  
Line Profiles ◽  
Galactic Field ◽  
Galactic Globular Clusters ◽  
Red Giant

AbstractWe determined zirconium abundance in the atmospheres of 327 red giant branch (RGB) stars in the globular cluster 47 Tuc. The 1D LTE abundances were obtained from the archival VLT GIRAFFE spectra, using 1D hydrostaticATLAS9 stellar model atmospheres and synthetic Zr I line profiles computed with theSYNTHE package. The average zirconium abundance determined in the sample of RGB stars, 〈[Zr/Fe]〉 = +0.38 ± 0.12, agrees well with zirconium abundances obtained at this metallicity in the Galactic field stars, as well as with those observed in other Galactic globular clusters.

scholarly journals Abundances of Mg and K in the atmospheres of turn-off starsin Galactic globular cluster 47 Tucanae

2018 ◽  
Vol 615 ◽  
pp. A173 ◽  
Author(s):  
A. Černiauskas ◽  
A. Kučinskas ◽  
J. Klevas ◽  
V. Dobrovolskas ◽  
S. Korotin ◽  
...  
Keyword(s):  
Globular Cluster ◽  
Spectral Synthesis ◽  
Statistical Significance ◽  
Three Dimensional ◽  
Stellar Model ◽  
Spectral Lines ◽  
Cluster Center ◽  
Light Elements ◽  
The One ◽  
Synthesis Methodology

Aims. We determined abundances of Mg and K in the atmospheres of 53 (Mg) and 75 (K) turn-off (TO) stars of the Galactic globular cluster 47 Tuc. The obtained abundances, together with those of Li, O, and Na that we had earlier determined for the same sample of stars, were used to search for possible relations between the abundances of K and other light elements, Li, O, Na, and Mg, as well as the connections between the chemical composition of TO stars and their kinematical properties. Methods. Abundances of Mg and K were determined using archival high resolution VLT FLAMES/GIRAFFE spectra, in combination with the one-dimensional (1D) non-local thermodynamic equilibrium (NLTE) spectral synthesis methodology. Spectral line profiles were computed with the MULTI code, using 1D hydrostatic ATLAS9 stellar model atmospheres. We also utilized three-dimensional (3D) hydrodynamical CO5BOLD and 1D hydrostatic LHD model atmospheres for computing 3D–1D LTE abundance corrections for the spectral lines of Mg and K, in order to assess the influence of convection on their formation in the atmospheres of TO stars. Results. The determined average abundance-to-iron ratios and their root mean square variations due to star-to-star abundance spreads were 〈[Mg/Fe]〉1D NLTE = 0.47 ± 0.12, and 〈[K/Fe]〉1D NLTE = 0.39 ± 0.09. Although the data suggest the possible existence of a weak correlation in the [K/Fe]–[Na/Fe] plane, its statistical significance is low. No statistically significant relations between the abundance of K and other light elements were detected. Also, we did not find any significant correlations or anti-correlations between the [Mg/Fe] and [K/Fe] ratios and projected distance from the cluster center. Similarly, no relations between the absolute radial velocities of individual stars and abundances of Mg and K in their atmospheres were detected. The 3D–1D abundance corrections were found to be small (≤0.1 dex) for the lines of Mg and K used in this study, thus indicating that the influence of convection on their formation is small.

scholarly journals On using dipolar modes to constrain the helium glitch in red giant stars

2020 ◽  
Vol 497 (1) ◽  
pp. 1008-1014
Author(s):  
G Dréau ◽  
M S Cunha ◽  
M Vrard ◽  
P P Avelino
Keyword(s):  
Acoustic Waves ◽  
Acoustic Mode ◽  
Stellar Model ◽  
Red Giants ◽  
Dipole Mode ◽  
Structural Variations ◽  
Giant Stars ◽  
Red Giant Stars ◽  
Red Giant ◽  
Additional Constraints

ABSTRACT The space-borne missions CoRoT and Kepler have revealed numerous mixed modes in red giant stars. These modes carry a wealth of information about red giant cores, but are of limited use when constraining rapid structural variations in their envelopes. This limitation can be circumvented if we have access to the frequencies of the pure acoustic dipolar modes in red giants, i.e. the dipole modes that would exist in the absence of coupling between gravity and acoustic waves. We present a pilot study aimed at evaluating the implications of using these pure acoustic mode frequencies in seismic studies of the helium structural variation in red giants. The study is based on artificial seismic data for a red giant branch stellar model, bracketing seven acoustic dipole radial orders around νmax. The pure acoustic dipole-mode frequencies are derived from a fit to the mixed-mode period spacings and then used to compute the pure acoustic dipole-mode second differences. The pure acoustic dipole-mode second differences inferred through this procedure follow the same oscillatory function as the radial-mode second differences. The additional constraints brought by the dipolar modes allow us to adopt a more complete description of the glitch signature when performing the fit to the second differences. The amplitude of the glitch retrieved from this fit is 15${{\ \rm per\ cent}}$ smaller than that from the fit based on the radial modes alone. Also, we find that thanks to the additional constraints, a bias in the inferred glitch location, found when adopting the simpler description of the glitch, is avoided.

scholarly journals The Hertzsprung-Russell Diagram of Metal-Poor Disk Stars

1978 ◽  
Vol 80 ◽  
pp. 273-276
Author(s):  
Sidney van den Bergh
Keyword(s):  
Velocity Field ◽  
Globular Cluster ◽  
High Velocity ◽  
Population Model ◽  
Open Cluster ◽  
Ultraviolet Excess ◽  
Red Giants ◽  
The Sun ◽  
The Galaxy ◽  
Red Giant

A quarter of a century ago Keenan and Keller (1953) showed that the majority of high-velocity stars near the Sun outline a Hertzsprung-Russell diagram similar to that of old Population I. This result, which did not appear to fit into Baade's (1944) two-population model of the Galaxy was ignored (except by Roman 1965) for the next two decades. Striking confirmation of the results of Keenan and Keller was, however, obtained by Hartwick and Hesser (1972). Their work appears to show that high-velocity field stars with an ultraviolet excess (which measures Fe/H) of δ(U-B) ≃ +0m.11 lie on a red giant branch that is more than a magnitude fainter than the giant branch of the strong-lined globular cluster 47 Tuc for which δ(U-B) ≃ +0m.10. Furthermore Demarque and McClure (1977) show that the red giants in the old metal poor [δ(U-B) ≃ +0m.11] open cluster NGC 2420 are significantly fainter than are those in 47 Tuc. Calculations by these authors show that the observed differences between the giants in 47 Tuc and in NGC 2420 can be explained if either (1) 47 Tuc is richer in helium than NGC 2420 by ΔY ≃ 0.1 or (2) if 47 Tuc has a ten times lower value of Z(CNO) than does NGC 2420.

scholarly journals Red Giants in Globular Clusters and Large-Scale Variations in The Galaxy

1980 ◽  
Vol 5 ◽  
pp. 817-826
Author(s):  
B. E. J. Pagel
Keyword(s):  
Recent Work ◽  
Globular Cluster ◽  
Globular Clusters ◽  
Large Scale ◽  
Red Giants ◽  
Mixing Effects ◽  
The Galaxy ◽  
Metal Abundance ◽  
Red Giant

SummaryThis review concerns recent work on the determination of overall metallicities [Fe/H] in a number of globular clusters and the systematics of mixing effects displayed (usually) by weak CH and strong CN. Special attention is given to the globular cluster ω Centauri, where both metal abundance variations and mixing effects occur and are closely intertwined. Recent observations carried out at the Anglo-Australian Telescope by E.A. Mallia and D.C. Watts have revealed large variations in the strength of metallic lines across the red giant branch of this cluster.

scholarly journals Chemical abundance analysis of red giant branch stars in the globular cluster E3

2018 ◽  
Vol 616 ◽  
pp. A181 ◽  
Author(s):  
L. Monaco ◽  
S. Villanova ◽  
G. Carraro ◽  
A. Mucciarelli ◽  
C. Moni Bidin
Keyword(s):  
Radial Velocity ◽  
Globular Cluster ◽  
Globular Clusters ◽  
Abundance Ratio ◽  
Chemical Abundance ◽  
Chemical Abundances ◽  
Multiple Populations ◽  
Red Giant ◽  
A Minor ◽  
Giant Branch Stars

Context. Globular clusters are known to host multiple stellar populations, which are a signature of their formation process. The globular cluster E3 is one of the few low-mass globulars that is thought not to host multiple populations. Aims. We investigate red giant branch stars in E3 with the aim of providing a first detailed chemical inventory for this cluster, we determine its radial velocity, and we provide additional insights into the possible presence of multiple populations in this cluster. Methods. We obtained high-resolution FLAMES-UVES/VLT spectra of four red giant branch stars likely members of E3. We performed a local thermodynamic equilibrium abundance analysis based on one-dimensional plane parallel ATLAS9 model atmospheres. Abundances were derived from line equivalent widths or spectrum synthesis. Results. We measured abundances of Na and of iron peak (Fe, V, Cr, Ni, Mn), α(Mg, Si, Ca, Ti), and neutron capture elements (Y, Ba, Eu). The mean cluster heliocentric radial velocity, metallicity, and sodium abundance ratio are νhelio = 12.6 ± 0.4 km s−1(σ = 0.6 ± 0.2 km s−1), [Fe/H] = −0.89 ± 0.08 dex, and [Na/Fe] = 0.18 ± 0.07 dex, respectively. The low Na abundance with no appreciable spread is suggestive of a cluster dominated by first-generation stars in agreement with results based on lower resolution spectroscopy. The low number of stars observed does not allow us to rule out a minor population of second-generation stars. The observed chemical abundances are compatible with the trends observed in Milky Way stars.

scholarly journals The Aarhus red giants challenge

2020 ◽  
Vol 635 ◽  
pp. A164 ◽  
Author(s):  
V. Silva Aguirre ◽  
J. Christensen-Dalsgaard ◽  
S. Cassisi ◽  
M. Miller Bertolami ◽  
A. Serenelli ◽  
...  
Keyword(s):  
Stellar Evolution ◽  
Main Sequence ◽  
Energy Generation ◽  
Abundance Ratio ◽  
Solar Radius ◽  
Stellar Mass ◽  
Stellar Structure ◽  
Red Giants ◽  
Numerical Implementation ◽  
Red Giant

Context. With the advent of space-based asteroseismology, determining accurate properties of red-giant stars using their observed oscillations has become the focus of many investigations due to their implications in a variety of fields in astrophysics. Stellar models are fundamental in predicting quantities such as stellar age, and their reliability critically depends on the numerical implementation of the physics at play in this evolutionary phase. Aims. We introduce the Aarhus red giants challenge, a series of detailed comparisons between widely used stellar evolution and oscillation codes that aim to establish the minimum level of uncertainties in properties of red giants arising solely from numerical implementations. We present the first set of results focusing on stellar evolution tracks and structures in the red-giant-branch (RGB) phase. Methods. Using nine state-of-the-art stellar evolution codes, we defined a set of input physics and physical constants for our calculations and calibrated the convective efficiency to a specific point on the main sequence. We produced evolutionary tracks and stellar structure models at a fixed radius along the red-giant branch for masses of 1.0 M⊙, 1.5 M⊙, 2.0 M⊙, and 2.5 M⊙, and compared the predicted stellar properties. Results. Once models have been calibrated on the main sequence, we find a residual spread in the predicted effective temperatures across all codes of ∼20 K at solar radius and ∼30–40 K in the RGB regardless of the considered stellar mass. The predicted ages show variations of 2–5% (increasing with stellar mass), which we attribute to differences in the numerical implementation of energy generation. The luminosity of the RGB-bump shows a spread of about 10% for the considered codes, which translates into magnitude differences of ∼0.1 mag in the optical V-band. We also compare the predicted [C/N] abundance ratio and find a spread of 0.1 dex or more for all considered masses. Conclusions. Our comparisons show that differences at the level of a few percent still remain in evolutionary calculations of red giants branch stars despite the use of the same input physics. These are mostly due to differences in the energy generation routines and interpolation across opacities, and they call for further investigation on these matters in the context of using properties of red giants as benchmarks for astrophysical studies.

scholarly journals Aluminium abundances in five discrete stellar populations of the globular cluster NGC 2808

2018 ◽  
Vol 615 ◽  
pp. A17 ◽  
Author(s):  
Eugenio Carretta ◽  
Angela Bragaglia ◽  
Sara Lucatello ◽  
Raffaele G. Gratton ◽  
Valentina D’Orazi ◽  
...  
Keyword(s):  
Globular Cluster ◽  
Cluster Formation ◽  
Light Elements ◽  
Atmospheric Parameters ◽  
Proton Capture ◽  
Full Dataset ◽  
Self Consistent ◽  
Red Giant ◽  
Set Up ◽  
First Time

We observed a sample of 90 red giant branch (RGB) stars in NGC 2808 using FLAMES/GIRAFFE and the high resolution grating with the set-up HR21. These stars have previous accurate atmospheric parameters and abundances of light elements. We derived aluminium abundances for them from the strong doublet Al i 8772–8773 Å as in previous works of our group. In addition, we were able to estimate the relative CN abundances for 89 of the stars from the strength of a large number of CN features. When adding self-consistent abundances from previous UVES spectra analysed by our team, we gathered [Al/Fe] ratios for a total of 108 RGB stars in NGC 2808. The full dataset of proton-capture elements is used to explore in detail the five spectroscopically detected discrete components in this globular cluster. We found that various classes of polluters are required to reproduce (anti)-correlations among all proton-capture elements in the populations P2, I1, and I2 with intermediate composition. This is in agreement with the detection of lithium in lower RGB second generation stars, requiring at least two kind of polluters. For chemically homogeneous populations, the best subdivision of our sample is into six components as derived from statistical cluster analysis. By comparing different diagrams [element/Fe] versus [element/Fe], we show for the first time that a simple dilution model is not able to reproduce all the subpopulations in this cluster. Polluters of different masses are required. NGC 2808 is confirmed to be a tough challenge to any scenario for globular cluster formation.

scholarly journals The globular cluster M10: reassessment of stellar membership, distance, and age using its variable and HB stars

2020 ◽  
Vol 499 (3) ◽  
pp. 4026-4039
Author(s):  
A Arellano Ferro ◽  
M A Yepez ◽  
S Muneer ◽  
I H Bustos Fierro ◽  
K P Schröder ◽  
...  
Keyword(s):  
Globular Cluster ◽  
Red Giants ◽  
Ccd Photometry ◽  
Shell Mass ◽  
Fourier Decomposition ◽  
Cluster Membership ◽  
Cluster Distance ◽  
The Mean ◽  
Red Giant ◽  
New Variables

ABSTRACT Time-series VI CCD photometry of the globular cluster M10 (NGC 6254) is employed to perform a detailed identification, inspection of their light curves, their classification, and their cluster membership, of all the known variables reported up to 2018. The membership analysis is based on the $Gaia$-DR2 positions and proper motions. The metallicity of the cluster is estimated based on the sole RRc star known in the cluster. The Fourier decomposition of its light curve leads to [Fe/H]$_{\rm ZW}$ = $-1.59 \pm 0.23$ dex. The mean cluster distance, estimated by several independent methods, is $5.0 \pm 0.3$ kpc. A multiapproach search in a region of about 10$\times$10 arcmin$^2$ around the cluster revealed three new variables, one SX Phe (V35) and two sinusoidal variables on the red giant branch (RGB) of unclear classification (V36 and V37). Modelling the HB stars is very sensitive to the stellar hydrogen shell mass, which surrounds the 0.50 $\mathrm{ M}_{\odot }$ helium core. To match the full stretch of the HB population, a range of total mass of 0.56–0.62 $\mathrm{ M}_{\odot }$ is required. These models support a distance of 5.35 kpc and an age of about 13 Gyr, and hint to some individual variation of the mass-loss on the upper RGB, perhaps caused by the presence of closed magnetic field in red giants.

scholarly journals Testing the intrinsic scatter of the asteroseismic scaling relations with Kepler red giants

2020 ◽  
Author(s):  
Yaguang Li ◽  
Timothy R Bedding ◽  
Dennis Stello ◽  
Sanjib Sharma ◽  
Daniel Huber ◽  
...  
Keyword(s):  
Stellar Model ◽  
Scaling Relations ◽  
Red Giants ◽  
Random Errors ◽  
Helium Burning ◽  
Exact Distributions ◽  
Synthetic Population ◽  
Red Giant ◽  
Stellar Masses ◽  
Intrinsic Scatter

Abstract Asteroseismic scaling relations are often used to derive stellar masses and radii, particulaly for stellar, exoplanet, and Galactic studies. It is therefore important that their precisions are known. Here we measure the intrinsic scatter of the underlying seismic scaling relations for Δν and νmax, using two sharp features that are formed in the H–R diagram (or related diagrams) by the red giant populations. These features are the edge near the zero-age core-helium-burning phase, and the strong clustering of stars at the so-called red giant branch bump. The broadening of those features is determined by factors including the intrinsic scatter of the scaling relations themselves, and therefore it is capable of imposing constraints on them. We modelled Kepler stars with a Galaxia synthetic population, upon which we applied the intrinsic scatter of the scaling relations to match the degree of sharpness seen in the observation. We found that the random errors from measuring Δν and νmax provide the dominating scatter that blurs the features. As a consequence, we conclude that the scaling relations have intrinsic scatter of $\sim 0.5\%$ (Δν), $\sim 1.1\%$ (νmax), $\sim 1.7\%$ (M) and $\sim 0.4\%$ (R), for the SYD pipeline measured Δν and νmax. This confirms that the scaling relations are very powerful tools. In addition, we show that standard evolution models fail to predict some of the structures in the observed population of both the HeB and RGB stars. Further stellar model improvements are needed to reproduce the exact distributions.

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