Evidence against Anomalous Compositions for Giants in the Galactic Nuclear Star Cluster

Thorsbro, B.; Ryde, Nils; Schultheis, M.; Hartman, Henrik; Rich, R. Michael; Lomaeva, Maria; Origlia, L.; Jönsson, Henrik

doi:10.3847/1538-4357/aadb97

Cited by 23 publications

(31 citation statements)

References 61 publications

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“…Yet another example is the study of abundances of M giants in the Galactic Center Nuclear Cluster by Do et al (2018) who found abnormal Sc, V, and Y abundances, again from K-band spectra. Their interpretation of the strong Sc I lines in terms of high abundances have, however, been questioned by Thorsbro et al (2018) since even nearby M giants are found to show similarly enhanced K-band Sc I lines, suggesting that they are affected by departures from LTE. Even for the warmer N-type carbon stars, detailed abundances are possible to derive from K and H band spectra (Lambert et al 1986).…”

Section: Cool Starsmentioning

confidence: 99%

High-precision stellar abundances of the elements: methods and applications

Nissen

Gustafsson

2018

Astron Astrophys Rev

102

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Efficient spectrographs at large telescopes have made it possible to obtain high-resolution spectra of stars with high signal-to-noise ratio and advances in model atmosphere analyses have enabled estimates of high-precision differential abundances of the elements from these spectra, i.e. with errors in the range 0.01 -0.03 dex for F, G, and K stars.Methods to determine such high-precision abundances together with precise values of effective temperatures and surface gravities from equivalent widths of spectral lines or by spectrum synthesis techniques are outlined, and effects on abundance determinations from using a 3D non-LTE analysis instead of a classical 1D LTE analysis are considered.The determination of high-precision stellar abundances of the elements have led to the discovery of unexpected phenomena and relations with important bearings on the astrophysics of galaxies, stars, and planets, i.e. i) Existence of discrete stellar populations within each of the main Galactic components (disk, halo, and bulge) providing new constraints on models for the formation of the Milky Way. ii) Differences in the relation between abundances and elemental condensation temperature for the Sun and solar twins suggesting dust-cleansing effects in proto-planetary disks and/or engulfment of planets by stars; iii) Differences in chemical composition between binary star components and between members of open or globular clusters showing that star-and cluster-formation processes are more complicated than previously thought; iv) Tight relations between some abundance ratios and age for solar-like stars providing new constraints on nucleosynthesis and Galactic chemical evolution models as well as the composition of terrestrial exoplanets.We conclude that if stellar abundances with precisions of 0.01 -0.03 dex can be achieved in studies of more distant stars and stars on the giant and supergiant branches, many more interesting future applications, of great relevance to stellar and galaxy evolution, are probable. Hence, in planning abundance surveys, it is important to carefully balance the need for large samples of stars against the spectral resolution and signal-to-noise ratio needed to obtain high-precision abundances. Furthermore, it is an advantage to work differentially on stars with similar atmospheric parameters, because then a simple 1D LTE analysis of stellar spectra may be sufficient. However, when determining high-precision absolute abundances or differential abundance between stars having more widely different parameters, e.g. metal-poor stars compared to the Sun or giants to dwarfs, then 3D non-LTE effects must be taken into account.

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Section: Cool Starsmentioning

confidence: 99%

High-precision stellar abundances of the elements: methods and applications

Nissen

Gustafsson

2018

Astron Astrophys Rev

102

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“…In general, weak lines form in deep layers, where the atmospheric structure is considered to be reasonably described by hydrostatic photospheric models. Therefore, weak molecular and atomic lines are often used for the determination of chemical composition in red giant stars in combination with hydrostatic photospheric models (e.g., Abia et al 2017;Gałan et al 2017;Rich et al 2017;Do et al 2018;D'Orazi et al 2018;Thorsbro et al 2018). Therefore, it is meaningful to see whether the AMBER data in these weak lines can be explained by the photosphere alone without the MOLsphere.…”

Section: Weak Molecular and Atomic Linesmentioning

confidence: 99%

Spatially resolving the atmosphere of the non-Mira-type AGB star SW Vir in near-infrared molecular and atomic lines with VLTI/AMBER

Ohnaka

Hadjara

Berna

2018

A&A

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Aims. We present a near-infrared spectro-interferometric observation of the non-Mira-type, semiregular asymptotic giant branch star SW Vir. Our aim is to probe the physical properties of the outer atmosphere with spatially resolved data in individual molecular and atomic lines. Methods. We observed SW Vir in the spectral window between 2.28 and 2.31 µm with the near-infrared interferometric instrument AMBER at ESO's Very Large Telescope Interferometer (VLTI). Results. Thanks to AMBER's high spatial resolution and high spectral resolution of 12 000, the atmosphere of SW Vir has been spatially resolved not only in strong CO first overtone lines but also in weak molecular and atomic lines of H 2 O, CN, HF, Ti, Fe, Mg, and Ca. While the uniform-disk diameter of the star is 16.23±0.20 mas in the continuum, it increases up to 22-24 mas in the CO lines. Comparison with the MARCS photospheric models reveals that the star appears larger than predicted by the hydrostatic models not only in the CO lines but also even in the weak molecular and atomic lines. We found that this is primarily due to the H 2 O lines (but also possibly due to the HF and Ti lines) originating in the extended outer atmosphere. Although the H 2 O lines manifest themselves very little in the spatially unresolved spectrum, the individual rovibrational H 2 O lines from the outer atmosphere can be identified in the spectro-interferometric data. Our modeling suggests an H 2 O column density of 10 19 -10 20 cm −2 in the outer atmosphere extending out to ∼2 R ⋆ . Conclusions. Our study has revealed that the effects of the nonphotospheric outer atmosphere are present in the spectrointerferometric data not only in the strong CO first overtone lines but also in the weak molecular and atomic lines. Therefore, analyses of spatially unresolved spectra, such as for example analyses of the chemical composition, should be carried out with care even if the lines appear to be weak.

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“…In this work, we summarize our findings first reported in Thorsbro et al [6] and discuss the atomic data needs in astrophysics on the basis of this.…”

Section: Introductionmentioning

confidence: 53%

“…We observed 18 stars in the Galactic center and eight stars located in the solar neighborhood. The exact information about the observations of these stars, as well as how they were analyzed were detailed by Thorsbro et al [6], Ryde et al [7], Rich et al [8]. All of the stars were of similar stellar classification, denominated M giants, which means that they had an effective temperature 1 between 3000 and 4000 K. The solar neighborhood stars were observed as a control group to compare the Galactic center stars.…”

Section: Observationsmentioning

confidence: 99%

Atomic Data Needs in Astrophysics: The Galactic Center “Scandium Mystery”

Thorsbro

2020

Atoms

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Investigating the Galactic center offers unique insights into the buildup and history of our Galaxy and is a stepping stone to understand galaxies in a larger context. It is reasonable to expect that the stars found in the Galactic center might have a different composition compared to stars found in the local neighborhood around the Sun. It is therefore quite exciting when recently there were reports of unusual neutral scandium, yttrium, and vanadium abundances found in the Galactic center stars, compared to local neighborhood stars. To explain the scandium abundances in the Galactic center, we turn to recent laboratory measurements and theoretical calculations done on the atomic oscillator strengths of neutral scandium lines in the near infrared. We combine these with measurements of the hyper fine splitting of neutral scandium. We show how these results can be used to explain the reported unusual scandium abundances and conclude that in this respect, the environment of the Galactic center is not that different from the environment in the local neighborhood around the sun.

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Evidence against Anomalous Compositions for Giants in the Galactic Nuclear Star Cluster

Cited by 23 publications

References 61 publications

High-precision stellar abundances of the elements: methods and applications

High-precision stellar abundances of the elements: methods and applications

Spatially resolving the atmosphere of the non-Mira-type AGB star SW Vir in near-infrared molecular and atomic lines with VLTI/AMBER

Atomic Data Needs in Astrophysics: The Galactic Center “Scandium Mystery”

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