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 Homogeneous analysis of globular clusters from the APOGEE survey with the BACCHUS code

2019 ◽  
Vol 622 ◽  
pp. A191 ◽  
Author(s):  
T. Masseron ◽  
D. A. García-Hernández ◽  
Sz. Mészáros ◽  
O. Zamora ◽  
F. Dell’Agli ◽  
...  
Keyword(s):  
Neutron Capture ◽  
Globular Clusters ◽  
Spectroscopic Method ◽  
Light Element ◽  
Asymptotic Giant Branch ◽  
Evolutionary Status ◽  
Large Set ◽  
Element Abundances ◽  
Wide Range ◽  
Automatic Code

Aims. We seek to provide abundances of a large set of light and neutron-capture elements homogeneously analyzed that cover a wide range of metallicity to constrain globular cluster (GC) formation and evolution models. Methods. We analyzed a large sample of 885 GCs giants from the SDSS IV-Apache Point Observatory Galactic Evolution Experiment (APOGEE) survey. We used the Cannon results to separate the red giant branch and asymptotic giant branch stars, not only allowing for a refinement of surface gravity from isochrones, but also providing an independent H-band spectroscopic method to distinguish stellar evolutionary status in clusters. We then used the Brussels Automatic Code for Characterizing High accUracy Spectra (BACCHUS) to derive metallicity, microturbulence, macroturbulence, many light-element abundances, and the neutron-capture elements Nd and Ce for the first time from the APOGEE GCs data. Results. Our independent analysis helped us to diagnose issues regarding the standard analysis of the APOGEE DR14 for low-metallicity GC stars. Furthermore, while we confirm most of the known correlations and anticorrelation trends (Na-O, Mg-Al, C-N), we discover that some stars within our most metal-poor clusters show an extreme Mg depletion and some Si enhancement. At the same time, these stars show some relative Al depletion, displaying a turnover in the Mg-Al diagram. These stars suggest that Al has been partially depleted in their progenitors by very hot proton-capture nucleosynthetic processes. Furthermore, we attempted to quantitatively correlate the spread of Al abundances with the global properties of GCs. We find an anticorrelation of the Al spread against clusters metallicity and luminosity, but the data do not allow us to find clear evidence of a dependence of N against metallicity in the more metal-poor clusters. Conclusions. Large and homogeneously analyzed samples from ongoing spectroscopic surveys unveil unseen chemical details for many clusters, including a turnover in the Mg-Al anticorrelation, thus yielding new constrains for GCs formation/evolution models.

scholarly journals An outer shade of Pal: Abundance analysis of the outer halo globular cluster Palomar 13

2019 ◽  
Vol 632 ◽  
pp. A55 ◽  
Author(s):  
Andreas Koch ◽  
Patrick Côté
Keyword(s):  
Globular Cluster ◽  
Neutron Capture ◽  
Milky Way ◽  
Signal To Noise Ratio ◽  
Light Element ◽  
Chemical Abundance ◽  
Galactocentric Distance ◽  
The Mean ◽  
Remote System ◽  
Kinematic Properties

At a Galactocentric distance of 27 kpc, Palomar 13 is an old globular cluster (GC) belonging to the outer halo. We present a chemical abundance analysis of this remote system from high-resolution spectra obtained with the Keck/HIRES spectrograph. Owing to the low signal-to-noise ratio of the data, our analysis is based on a coaddition of the spectra of 18 member stars. We are able to determine integrated abundance ratios for 16 species of 14 elements, of α-elements (Mg, Si, Ca, and Ti), Fe-peak (Sc, Mn, Cr, Ni, Cu, and Zn), and neutron-capture elements (Y and Ba). While the mean Na abundance is found to be slightly enhanced and halo-like, our method does not allow us to probe an abundance spread that would be expected in this light element if multiple populations are present in Pal 13. We find a metal-poor mean metallicity of −1.91 ± 0.05 (statistical) ±0.22 (systematic), confirming that Pal 13 is a typical metal-poor representative of the outer halo. While there are some differences between individual α-elements, such as halo-like Mg and Si versus the mildly lower Ca and Ti abundances, the mean [α/Fe] of 0.34 ± 0.06 is consistent with the marginally lower α component of the halo field and GC stars at similar metallicity. We discuss our results in the context of other objects in the outer halo and consider which of these objects were likely accreted. We also discuss the properties of their progenitors. While chemically, Pal 13 is similar to Gaia-Enceladus and some of its GCs, this is not supported by its kinematic properties within the Milky Way system. Moreover, its chemodynamical similarity with NGC 5466, a purported progeny of the Sequoia accretion event, might indicate a common origin in this progenitor. However, the ambiguities in the full abundance space of this comparison emphasize the difficulties in unequivocally labeling a single GC as an accreted object, let alone assigning it to a single progenitor.

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 Chemical Composition of Planet-harboring Stars

2004 ◽  
Vol 202 ◽  
pp. 136-138
Author(s):  
G. Zhao ◽  
Y. Q. Chen ◽  
H. M. Qiu ◽  
S. K. Tang ◽  
Z. W. Li
Keyword(s):  
Chemical Composition ◽  
Signal To Noise Ratio ◽  
Giant Planet ◽  
Astronomical Observatory ◽  
High Signal ◽  
Chemical Abundance ◽  
Signal To Noise ◽  
Echelle Spectrograph ◽  
Abundance Patterns ◽  
High Metallicity

Based on the high-resolution, high signal-to-noise ratio spectra collected with the coudé echelle spectrograph attached to the 2.16m telescope at Beijing Astronomical Observatory, we determined the chemical abundance patterns for a sample of six planet-harboring stars. The result is used to investigate the connection between giant planet and high metallicity and to probe the influence of this process on other elements.

scholarly journals Mixed poloidal–toroidal magnetic configuration and surface abundance distributions of the Bp star 36 Lyn★

2017 ◽  
Vol 473 (3) ◽  
pp. 3367-3376 ◽  
Author(s):  
M. E. Oksala ◽  
J. Silvester ◽  
O. Kochukhov ◽  
C. Neiner ◽  
G. A. Wade ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Strong Magnetic Field ◽  
Signal To Noise Ratio ◽  
Doppler Imaging ◽  
High Signal ◽  
Distinct Region ◽  
Chemical Abundance ◽  
Radial Magnetic Field ◽  
Inhomogeneous Surface ◽  
Radial Field

Abstract Previous studies of the chemically peculiar Bp star 36 Lyn revealed a moderately strong magnetic field, circumstellar material and inhomogeneous surface abundance distributions of certain elements. We present in this paper an analysis of 33 high signal-to-noise ratio, high-resolution Stokes IV observations of 36 Lyn obtained with the Narval spectropolarimeter at the Bernard Lyot Telescope at Pic du Midi Observatory. From these data, we compute new measurements of the mean longitudinal magnetic field, Bℓ, using the multiline least-squares deconvolution (LSD) technique. A rotationally phased Bℓ curve reveals a strong magnetic field, with indications for deviation from a pure dipole field. We derive magnetic maps and chemical abundance distributions from the LSD profiles, produced using the Zeeman–Doppler imaging code InversLSD. Using a spherical harmonic expansion to characterize the magnetic field, we find that the harmonic energy is concentrated predominantly in the dipole mode (ℓ = 1), with significant contribution from both the poloidal and toroidal components. This toroidal field component is predicted theoretically, but not typically observed for Ap/Bp stars. Chemical abundance maps reveal a helium enhancement in a distinct region where the radial magnetic field is strong. Silicon enhancements are located in two regions, also where the radial field is stronger. Titanium and iron enhancements are slightly offset from the helium enhancements, and are located in areas where the radial field is weak, close to the magnetic equator.

scholarly journals Abundances and kinematics of carbon-enhanced metal-poor stars in the Galactic halo

2019 ◽  
Vol 623 ◽  
pp. A128 ◽  
Author(s):  
C. J. Hansen ◽  
T. T. Hansen ◽  
A. Koch ◽  
T. C. Beers ◽  
B. Nordström ◽  
...  
Keyword(s):  
Neutron Star ◽  
Neutron Capture ◽  
Galactic Halo ◽  
Asymptotic Giant Branch ◽  
Elemental Abundance ◽  
High Signal ◽  
Galactic Centre ◽  
Agb Stars ◽  
Orbital Parameters ◽  
Wide Range

Carbon-enhanced metal-poor (CEMP) stars span a wide range of stellar populations, from bona fide second-generation stars to later-forming stars that provide excellent probes of binary mass transfer and stellar evolution. Here we analyse 11 metal-poor stars (8 of which are new to the literature), and demonstrate that 10 are CEMP stars. Based on high signal-to-noise ratio (S/N) X-shooter spectra, we derive abundances of 20 elements (C, N, O, Na, Mg, Ca, Sc, Ti, Cr, Mn, Fe, Ni, Sr, Y, Ba, La, Ce, Pr, Nd, and Eu). From the high-S/N spectra, we were able to trace the chemical contribution of the rare earth elements (REE) from various possible production sites, finding a preference for metal-poor low-mass asymptotic giant branch (AGB) stars of 1.5 M⊙ in CEMP-s stars, while CEMP-r/s stars may indicate a more massive AGB contribution (2–5 M⊙). A contribution from the r-process – possibly from neutron star–neutron star mergers (NSM) – is also detectable in the REE stellar abundances, especially in the CEMP-r/s sub-group rich in both slow(s) and rapid(r) neutron-capture elements. Combining spectroscopic data with Gaia DR2 astrometric data provides a powerful chemodynamical tool for placing CEMP stars in the various Galactic components, and classifying CEMP stars into the four major elemental-abundance sub-groups, which are dictated by their neutron-capture element content. The derived orbital parameters indicate that all but one star in our sample (and the majority of the selected literature stars) belong to the Galactic halo. These stars exhibit a median orbital eccentricity of 0.7, and are found on both prograde and retrograde orbits. We find that the orbital parameters of CEMP-no and CEMP-s stars are remarkably similar in the 98 stars we study. A special case is the CEMP-no star HE 0020−1741, with very low Sr and Ba content, which possesses the most eccentric orbit among the stars in our sample, passing close to the Galactic centre. Finally, we propose an improved scheme to sub-classify the CEMP stars, making use of the Sr/Ba ratio, which can also be used to separate very metal-poor stars from CEMP stars. We explore the use of [Sr/Ba] versus [Ba/Fe] in 93 stars in the metallicity range −4.2 ≲ [Fe/H] <  −2. We show that the Sr/Ba ratio can also be successfully used for distinguishing CEMP-s, CEMP-r/s, and CEMP-no stars. Additionally, the Sr/Ba ratio is found to be a powerful astro-nuclear indicator, since the metal-poor AGB stars exhibit very different Sr/Ba ratios compared to fast-rotating massive stars and NSM, and is also reasonably unbiased by NLTE and 3D corrections.

scholarly journals A Spectroscopic Study of Barium Stars

2008 ◽  
Vol 4 (S252) ◽  
pp. 425-426
Author(s):  
G. Q. Liu ◽  
Y. C. Liang ◽  
L. Deng
Keyword(s):  
Neutron Capture ◽  
Binary Systems ◽  
Signal To Noise Ratio ◽  
High Signal ◽  
Agb Stars ◽  
Atmospheric Parameters ◽  
Chemical Abundances ◽  
Capture Process ◽  
Abundance Patterns ◽  
Process Elements

AbstractWe present an analysis of eight barium stars, providing their atmospheric parameters (Teff, log g, [Fe/H], ξt) and chemical abundances, based on the high signal-to-noise ratio and high resolution Echelle spectra. The s-process elements Y, Zr, Ba, La, Eu show obvious overabundance relative to the Sun. And Na, Mg, Al, Si, Ca, Sc, Ti, V, Cr, Mn, Ni show comparable abundances to the Solar ones. The results of theoretical model of wind accretion for binary systems can explain the observed abundance patterns of the neutron capture process elements in these Ba stars, which means that their overabundant heavy-elements could be caused by accreting the ejecta of AGB stars, the progenitors of the present white dwarf companions in the binary systems.

scholarly journals Omega Centauri: weak MgH band in red giants directly traces the helium content

2020 ◽  
Vol 495 (1) ◽  
pp. 383-401
Author(s):  
Arumalla B S Reddy
Keyword(s):  
Signal To Noise Ratio ◽  
Asymptotic Giant Branch ◽  
High Spectral Resolution ◽  
High Signal ◽  
Synthetic Spectrum ◽  
Red Giants ◽  
Chemical Abundances ◽  
Rich Cluster ◽  
Red Giant ◽  
The Impact

ABSTRACT High spectral resolution and high signal-to-noise ratio optical spectra of red giants in the globular cluster Omega Centauri are analysed for stellar parameters and chemical abundances of 15 elements including helium by either line equivalent widths or synthetic spectrum analyses. The simultaneous abundance analysis of MgH and Mg lines adopting theoretical photospheres and a combination of He/H ratios proved to be the only powerful probe to evaluate helium abundances of red giants cooler than 4400 K, wherein otherwise helium line transitions (He i 10830 and 5876 Å) present for a direct spectral line analysis. The impact of helium-enhanced model photospheres on the resulting abundance ratios is smaller than 0.15 dex, in agreement with past studies. The first indirect spectroscopic helium abundances measured in this paper for the most metal-rich cluster members reveal the discovery of seven He-enhanced giants ($\Delta Y=+0.15 \pm 0.04$), the largest such sample found spectroscopically to date. The average metallicity of −0.79 ± 0.06 dex and abundances for O, Na, Al, Si, Ca, Ti, Ni, Ba, and La are consistent with values found for the red giant branch (RGB-a) and subgiant branch (SGB-a) populations of Omega Centauri, suggesting an evolutionary connection among samples. The He enhancement in giants is associated with larger s-process elemental abundances, which correlate with Al and anticorrelate with O. These results support the formation of He-enhanced, metal-rich population of Omega Centauri out of the interstellar medium enriched with the ejecta of fast rotating massive stars, binaries exploding as supernovae, and asymptotic giant branch (AGB) stars.

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.

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