1. |
- Albert, Damien, et al.
(författare)
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A Decade with VAMDC : Results and Ambitions
- 2020
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Ingår i: Atoms. - : MDPI. - 2218-2004. ; 8:4
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents an overview of the current status of the Virtual Atomic and Molecular Data Centre (VAMDC) e-infrastructure, including the current status of the VAMDC-connected (or to be connected) databases, updates on the latest technological development within the infrastructure and a presentation of some application tools that make use of the VAMDC e-infrastructure. We analyse the past 10 years of VAMDC development and operation, and assess their impact both on the field of atomic and molecular (A&M) physics itself and on heterogeneous data management in international cooperation. The highly sophisticated VAMDC infrastructure and the related databases developed over this long term make them a perfect resource of sustainable data for future applications in many fields of research. However, we also discuss the current limitations that prevent VAMDC from becoming the main publishing platform and the main source of A&M data for user communities, and present possible solutions under investigation by the consortium. Several user application examples are presented, illustrating the benefits of VAMDC in current research applications, which often need the A&M data from more than one database. Finally, we present our vision for the future of VAMDC.
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2. |
- Rusomarov, Naum, 1986-, et al.
(författare)
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Magnetic Doppler imaging of the chemically peculiar star HD 125248
- 2016
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Ingår i: Astronomy and Astrophysics. - Paris : EDP Sciences. - 0004-6361 .- 1432-0746. ; 588
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Tidskriftsartikel (refereegranskat)abstract
- Context. Intermediate-mass, chemically peculiar stars with strong magnetic fields provide an excellent opportunity to study the topology of their surface magnetic fields and the interplay between magnetic geometries and abundance inhomogeneities in the atmospheres of these stars. Aims. We reconstruct detailed maps of the surface magnetic field and abundance distributions for the magnetic Ap star HD125248. Methods. We performed the analysis based on phase-resolved, four Stokes parameter spectropolarimetric observations obtained with the HARPSpol instrument. These data were interpreted with the help of magnetic Doppler imaging techniques and model atmospheres taking the effects of strong magnetic fields and nonsolar chemical composition into account. Results. We improved the atmospheric parameters of the star, T-eff = 9850 +/- 250K and log g = 4.05 +/- 0.10. We performed detailed abundance analysis, which confirmed that HD125248 has abundances typical of other Ap stars, and discovered significant vertical stratification effects for the FeII and CrII ions. We computed LSD Stokes profiles using several line masks corresponding to Fe-peak and rare earth elements, and studied their behavior with rotational phase. Combining previous longitudinal field measurements with our own observations, we improved the rotational period of the star Prot = 9.29558 +/- 0.00006 d. Magnetic Doppler imaging of HD125248 showed that its magnetic field is mostly poloidal and quasi-dipolar with two large spots of different polarity and field strength. The chemical maps of Fe, Cr, Ce, Nd, Gd, and Ti show abundance contrasts of 0.9-3.5 dex. Among these elements, the Fe abundance map does not show high-contrast features. Cr is overabundant around the negative magnetic pole and has 3.5 dex abundance range. The rare earth elements and Ti are overabundant near the positive magnetic pole. Conclusions. The magnetic field of HD125248 has strong deviations from the classical oblique dipole field geometry. A comparison of the magnetic field topology of HD125248 with the results derived for other stars using four Stokes magnetic Doppler imaging suggests evidence that the field topology becomes simpler with increasing age. The abundance maps show weak correlation with magnetic field geometry, but they do not agree with the theoretical atomic diffusion calculations, which predict element accumulation in the horizontal field regions.
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3. |
- Ryabchikova, Tatiana, et al.
(författare)
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Using Molecular Lines to Determine Carbon and Nitrogen Abundances in the Atmospheres of Cool Stars
- 2022
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Ingår i: Atoms. - : MDPI. - 2218-2004. ; 10:4
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Tidskriftsartikel (refereegranskat)abstract
- Simultaneous analysis of the C2 and CN molecular bands in the 5100–5200 and 7930–8100 Å spectral regions is a promising alternative for the accurate determination of the carbon (C) and nitrogen (N) abundance in the atmospheres of the solar-like stars. Practical implementation of this new method became possible after recent improvements of the molecular constants for both molecules. The new molecular data predicted the correct line strength and line positions; therefore, they were included in the Vienna Atomic Line Database (VALD), which is widely used by astronomers and spectroscopists. In this paper, we demonstrate that the molecular data analysis provides C and, in particular, N abundances consistent with those derived from the atomic lines. We illustrate this by performing the analysis for three stars. Our results provide strong arguments for using the combination of C2 and CN molecular lines for accurate nitrogen abundance determination keeping in mind the difficulties of using the N i lines in the observed spectra of the solar-like stars.
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4. |
- Ryabchikova, Tatiana, et al.
(författare)
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VALD : The Meeting Point of Data Producers and Data Users
- 2018
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Ingår i: Galaxies. - : MDPI. - 2075-4434. ; 6:3
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Tidskriftsartikel (refereegranskat)abstract
- Vienna Atomic Line Database (VALD) contains data on atomic and molecular energy levels and parameters of spectral lines required for stellar spectra analysis. Hundreds of millions of lines for fine spectral synthesis and for opacity calculations are collected in the present version of VALD (VALD3). Critical evaluation of the data and the diversity of extraction tools support the high popularity of VALD among users. The data model of VALD3 incorporates obligatory links to the bibliography making our database more attractive as a publishing platform for data producers. The VALD data quality and completeness are constantly improving allowing better reproduction of stellar spectra. To illustrate continuous evolution of the data content we present a comparative analysis of the recent experimental and theoretical atomic data for Fe-group elements, which will be included in the next VALD release. This release will also include a possibility for extracting the line data with full isotopic and hyperfine structures.
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