scholarly journals The 9th Magnitude CEMP star BD+44°493: Origin of its Carbon Excess and Beryllium Abundance

2009 ◽  
Vol 5 (S265) ◽  
pp. 124-125 ◽  
Author(s):  
Hiroko Ito ◽  
Wako Aoki ◽  
Satoshi Honda ◽  
Timothy C. Beers ◽  
Nozomu Tominaga
Keyword(s):  
First Generation ◽  
Apparent Magnitude ◽  
Chemical Abundance ◽  
Abundance Pattern ◽  
Upper Limit ◽  
Carbon Excess

AbstractWe performed a chemical abundance analysis of the very bright (V = 9.1) carbon-enhanced metal-poor (CEMP) star BD+44°493, which is the first star found with metallicity [Fe/H] < −3.5 and an apparent magnitude V < 12. The star is classified as a CEMP-no” subgiant, and its abundance pattern implies that a first-generation faint supernova is the most likely origin of its carbon excess. We set an very low upper limit on this star's beryllium abundance, which demonstrates that high C and O abundances do not necessarily imply high Be abundances.

scholarly journals LAMOST J011939.222−012150.45: The most barium-enhanced CEMP-s turnoff star

2019 ◽  
Vol 71 (5) ◽  
Author(s):  
Shilin Zhang ◽  
Haining Li ◽  
Gang Zhao ◽  
Wako Aoki ◽  
Tadafumi Matsuno
Keyword(s):  
Neutron Capture ◽  
Signal To Noise Ratio ◽  
Asymptotic Giant Branch ◽  
Velocity Variation ◽  
High Signal ◽  
Evolutionary Status ◽  
Chemical Abundance ◽  
Abundance Pattern ◽  
Radial Velocity Variation ◽  
Carbon Excess

Abstract We have performed chemical abundance analyses for a newly discovered metal-poor turn-off star (Teff = 6276 K, log g = 3.93, [Fe$/$H] = −2.93), LAMOST J011939.222−012150.45, based on high-resolution and high signal-to-noise ratio spectra in both optical and near-UV obtained by Subaru. Abundances have been derived for 20 elements, including 11 light elements such as C, N, Na, Mg, etc., and 9 neutron-capture elements from Sr to Pb. This object is a carbon-enhanced metal-poor star with a large carbon excess of [C$/$Fe] = +2.26. LAMOST J011939.222−012150.45 shows extreme enhancement in s-process elements, especially for Ba, La, and Pb ([Ba$/$Fe] = +3.16 ± 0.18, [La$/$Fe] = +2.29 ± 0.24, [Pb$/$Fe] = +3.38 ± 0.12). A very clear radial velocity variation has also been detected, providing evidence of the existence of a companion. Interestingly, even without any scaling, the observed abundance pattern from light to heavy neutron-capture elements agrees well with predictions of accretion from a companion asymptotic giant branch (AGB) star. Considering the evolutionary status of this object, its surface material is very likely to be completely accreted from its AGB companion and has been preserved until today.

scholarly journals The R-process Alliance: The Peculiar Chemical Abundance Pattern of RAVE J183013.5−455510

2020 ◽  
Vol 897 (1) ◽  
pp. 78 ◽  
Author(s):  
Vinicius M. Placco ◽  
Rafael M. Santucci ◽  
Zhen Yuan ◽  
Mohammad K. Mardini ◽  
Erika M. Holmbeck ◽  
...  
Keyword(s):  
Chemical Abundance ◽  
Abundance Pattern ◽  
R Process

scholarly journals A precise asteroseismic age and metallicity for HD 139614: a pre-main-sequence star with a protoplanetary disc in Upper Centaurus–Lupus

2021 ◽  
Vol 502 (2) ◽  
pp. 1633-1646
Author(s):  
Simon J Murphy ◽  
Meridith Joyce ◽  
Timothy R Bedding ◽  
Timothy R White ◽  
Mihkel Kama
Keyword(s):  
Main Sequence ◽  
Main Sequence Star ◽  
Radial Pulsation ◽  
Chemical Abundance ◽  
Abundance Pattern ◽  
Intermediate Mass Stars ◽  
Metal Abundance ◽  
Ring Structures ◽  
Stellar Oscillation

ABSTRACT HD 139614 is known to be a ∼14-Myr-old, possibly pre-main-sequence star in the Sco-Cen OB association in the Upper Centaurus-Lupus subgroup, with a slightly warped circumstellar disc containing ring structures hinting at one or more planets. The star’s chemical abundance pattern is metal-deficient except for volatile elements, which places it in the λ Boo class and suggests it has recently accreted gas-rich but dust-poor material. We identify seven dipole and four radial pulsation modes among its δ Sct pulsations using the TESS light curve and an échelle diagram. Precision modelling with the mesa stellar evolution and gyre stellar oscillation programs confirms it is on the pre-main sequence. Asteroseismic, grid-based modelling suggests an age of 10.75 ± 0.77 Myr, a mass of 1.52 ± 0.02 M ⊙, and a global metal abundance of Z = 0.0100 ± 0.0010. This represents the first asteroseismic determination of the bulk metallicity of a λ Boo star. The precise age and metallicity offer a benchmark for age estimates in Upper Centaurus–Lupus, and for understanding disc retention and planet formation around intermediate-mass stars.

scholarly journals Corotation: Its Influence on the Chemical Abundance Pattern of the Galaxy

2002 ◽  
Vol 571 (2) ◽  
pp. L113-L115 ◽  
Author(s):  
Yu. N. Mishurov ◽  
J. R. D. Lépine ◽  
I. A. Acharova
Keyword(s):  
Chemical Abundance ◽  
Abundance Pattern ◽  
The Galaxy

scholarly journals Observations of the Ultraviolet-Bright Star Barnard 29 in the Globular Cluster M13 (NGC 6205)

2018 ◽  
Vol 14 (S343) ◽  
pp. 385-386
Author(s):  
William V. Dixon ◽  
Pierre Chayer ◽  
I. N. Reid ◽  
Marcelo Miguel Miller Bertolami
Keyword(s):  
Optical Spectrum ◽  
First Generation ◽  
Complex Shape ◽  
Stellar Atmosphere ◽  
Bright Star ◽  
Abundance Pattern ◽  
Cluster Distance ◽  
Iron Abundance ◽  
Significant Chemical ◽  
Best Fit

AbstractWe have analyzed FUSE, COS, GHRS, and Keck/HIRES spectra of the UV-bright star Barnard 29 in M13. Fits to the star’s optical spectrum yield Teff = 20,000 ± 100 K and log g = 3.00 ± 0.01. Using modern stellar-atmosphere models, we are able to reproduce the complex shape of the Balmer H.. feature. We derive photospheric abundances of He, C, N, O, Mg, Al, Si, P, S, Cl, Ar, Ti, Cr, Fe, Ni, and Ge. Barnard 29 exhibits an abundance pattern typical of the first-generation stars in M13, enhanced in oxygen and depleted in aluminum. We see no evidence of significant chemical evolution since the star left the RGB; in particular, it did not undergo third dredge-up. Previous workers found that the star’s FUV spectra yield an iron abundance about 0.5 dex lower than its optical spectrum, but the iron abundances derived from all of our spectra are consistent with one another and with the cluster value. We attribute this difference to our use of model atmospheres without microturbulence. By comparing our best-fit model with the star’s optical magnitudes, we derive a mass M*/M=0.40 − 0.49 and luminosity log L*/L⊙=3.20 − 3.29, depending on the cluster distance. Comparison with stellar-evolution models suggests that Barnard 29 evolved from a ZAHB star of mass M*/M⊙∼0.50, placing it near the boundary between the extreme and blue horizontal branches.

scholarly journals Updated theoretical period–age and period–age–colour relations for Galactic Classical Cepheids: an application to the Gaia DR2 sample

2020 ◽  
Vol 496 (4) ◽  
pp. 5039-5051
Author(s):  
Giulia De Somma ◽  
Marcella Marconi ◽  
Santi Cassisi ◽  
Vincenzo Ripepi ◽  
Silvio Leccia ◽  
...  
Keyword(s):  
Mass Loss ◽  
Age Distribution ◽  
Theoretical Framework ◽  
Distribution Analysis ◽  
Chemical Abundance ◽  
Instability Strip ◽  
Abundance Pattern ◽  
The Core ◽  
Classical Cepheids ◽  
The Impact

ABSTRACT Updated evolutionary and pulsational model predictions are combined in order to interpret the properties of Galactic Classical Cepheids in the Gaia Data Release 2. In particular, the location of the instability strip boundaries and the analytical relations connecting pulsation periods to the intrinsic stellar parameters are combined with evolutionary tracks to derive reliable and accurate period–age and the first theoretical period–age–colour relations in the Gaia bands for a solar chemical abundance pattern (Z = 0.02, Y = 0.28). The adopted theoretical framework takes into account possible variations in the mass–luminosity relation for the core helium-burning stage as due to changes in the core convective overshooting and/or mass-loss efficiency, as well as the impact on the instability strip boundaries due to different assumptions for superadiabatic convection efficiency. The inferred period–age and period–age–colour relations are applied to a selected sample of both fundamental and first overtone Gaia Cepheids, and individual ages for the various adopted theoretical scenarios are derived. The retrieved age distributions confirm that a variation in the efficiency of superadiabatic convection in the pulsational model computations has a negligible effect, whereas a brighter mass–luminosity relation, as produced by mild overshooting, rotation, or mass-loss, implies significantly older age predictions. Moreover, older Cepheids are found at larger Galactocentric distances, while first overtone Cepheids are found to be systematically older than the fundamental ones. The comparison with independent age distribution analysis in literature supports the predictive capability of current theoretical framework.

scholarly journals Explosive nucleosynthesis of a metal-deficient star as the source of a distinct odd-even effect in the solar twin HIP 11915

2021 ◽  
Vol 502 (1) ◽  
pp. L104-L109
Author(s):  
Jhon Yana Galarza ◽  
Jorge Meléndez ◽  
Amanda I Karakas ◽  
Martin Asplund ◽  
Diego Lorenzo-Oliveira
Keyword(s):  
Signal To Noise Ratio ◽  
Resolving Power ◽  
Core Collapse ◽  
The Sun ◽  
Chemical Abundance ◽  
Abundance Pattern ◽  
Chemical Enrichment ◽  
Abundance Patterns ◽  
Solar Metallicity ◽  
First Time

ABSTRACT The abundance patterns observed in the Sun and in metal-poor stars show a clear odd-even effect. An important question is whether the odd-even effect in solar-metallicity stars is similar to the Sun, or if there are variations that can tell us about different chemical enrichment histories. In this work, we report for the first time observational evidence of a differential odd-even effect in the solar twin HIP 11915, relative to the solar odd-even abundance pattern. The spectra of this star were obtained with high-resolving power (140 000) and signal-to-noise ratio (∼420) using the ESPRESSO spectrograph and the VLT telescope. Thanks to the high spectral quality, we obtained extremely precise stellar parameters (σ(Teff) = 2 K, $\sigma (\rm {[Fe/H]})$ = 0.003 dex, and σ(log g) = 0.008 dex). We determine the chemical abundance of 20 elements (Z ≤ 39) with high precision (∼0.01 dex), which shows a strong pattern of the odd-even effect even after performing galactic chemical evolution corrections. The odd-even effect is reasonably well-reproduced by a core-collapse supernova of 13 $\rm {M_{\odot }}$ and metallicity Z = 0.001 diluted into a metal-poor gas of 1 $\rm {M_{\odot }}$. Our results indicate that HIP 11915 has an odd-even effect slightly different than the Sun, thus confirming a different supernova enrichment history.

scholarly journals Modelling depletion by re-accretion of gas from a dusty disc in post-AGB stars

2019 ◽  
Vol 629 ◽  
pp. A49 ◽  
Author(s):  
Glenn-Michael Oomen ◽  
Hans Van Winckel ◽  
Onno Pols ◽  
Gijs Nelemans
Keyword(s):  
Asymptotic Giant Branch ◽  
Condensation Temperature ◽  
Agb Stars ◽  
Chemical Abundance ◽  
Abundance Pattern ◽  
Refractory Elements ◽  
Accretion Rates ◽  
Low Mass ◽  
Red Giant ◽  
Chemical Peculiarity

Many disc-type post-asymptotic giant branch (post-AGB) stars are chemically peculiar, showing underabundances of refractory elements in their photospheres that correlate with condensation temperature. The aim of this paper is to investigate how accretion from a circumbinary disc can cause this phenomenon of depletion and how this impacts the evolution of post-AGB stars. We used the MESA code to evolve stars in the post-AGB phase, while including accretion of metal-poor gas. We compared the models to a sample of 58 observed disc-type post-AGB stars with chemical abundance data. For each of these stars, we estimated the luminosity and the mass using the Gaia distance. We modelled the accretion rate onto the binary from a viscously evolving disc for a range of initial accretion rates and disc masses. We find that large initial accretion rates (≳3  ×  10−7 M⊙ yr−1) and large initial disc masses (∼10−2 M⊙) are needed to reproduce the observed depleted post-AGB stars. Based on these high accretion rates, the evolution timescale of post-AGB stars can be significantly extended by a factor between two and five. We distinguish depletion patterns that are unsaturated (plateau profile) from those that are saturated, and we expect that post-red giant branch (post-RGB) stars are much more likely to show an unsaturated abundance pattern compared to post-AGB stars. Finally, because of the slower evolution of the low-mass post-RGB stars, we find that these systems can become depleted at lower effective temperatures (<5000 K). We conclude that accretion from a circumbinary disc successfully accounts for the chemical peculiarity of post-AGB stars.

scholarly journals Moving Groups in the Galactic Disc

2013 ◽  
Vol 9 (S298) ◽  
pp. 77-82
Author(s):  
P. Ramya ◽  
B. E. Reddy
Keyword(s):  
Open Clusters ◽  
Galactic Disc ◽  
Chemical Abundance ◽  
Abundance Pattern ◽  
Thick Disc ◽  
Thin Disc ◽  
Stellar Streams ◽  
Moving Groups ◽  
Rule Out

AbstractWe present results of chemical abundance study of a few representative stellar streams of Galactic thick and thin discs. Arcturus stream, which was proposed to have an extragalactic origin, and a recently detected stream called AF06 were studied. Results show a range of metallicity, age and abundance pattern that are consistent with those of Galactic thick disc component. We found similar results for AF06. The abundance and age results unambiguously rule out the possibility that the member stars are vestiges of open clusters. Abundance results of a sample of stars of Sirius and Hercules streams combined with the kinematics show that both the streams belong to the thin disc component. Also, results rule out these are remnants of open clusters. It is likely these streams formed insitu due to perturbations caused by non-axisymmetric components such as bar or spirals.

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