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- Nesvacil, N., et al.
(författare)
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Multi-element Doppler imaging of the CP2 star HD 3980
- 2012
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 537
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Tidskriftsartikel (refereegranskat)abstract
- Context. In atmospheres of magnetic main-sequence stars, the diffusion of chemical elements leads to a number of observed anomalies, such as abundance spots across the stellar surface. Aims. The aim of this study was to derive a detailed picture of the surface abundance distribution of the magnetic chemically peculiar star HD 3980. Methods. Based on high-resolution, phase-resolved spectroscopic observations of the magnetic A-type star HD 3980, the inhomogeneous surface distribution of 13 chemical elements (Li, O, Si, Ca, Cr, Mn, Fe, La, Ce, Pr, Nd, Eu, and Gd) has been reconstructed. The INVERS12 code was used to invert the rotational variability in line profiles to elemental surface distributions. Results. Assuming a centered, dominantly dipolar magnetic field configuration, we find that Li, O, Mg, Pr, and Nd are mainly concentrated in the area of the magnetic poles and depleted in the regions around the magnetic equator. The high abundance spots of Si, La, Ce, Eu, and Gd are located between the magnetic poles and the magnetic equator. Except for La, which is clearly depleted in the area of the magnetic poles, no obvious correlation with the magnetic field has been found for these elements otherwise. Ca, Cr, and Fe appear enhanced along the rotational equator and the area around the magnetic poles. The intersection between the magnetic and the rotational equator constitutes an exception, especially for Ca and Cr, which are depleted in that region. Conclusions. No obvious correlation between the theoretically predicted abundance patterns and those determined in this study could be found. This can be attributed to a lack of up-to-date theoretical models, especially for rare earth elements.
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| 6. |
- Lueftinger, T., et al.
(författare)
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Surface structure of the CoRoT CP2 target star HD50773
- 2010
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 509:1, s. A43-
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Tidskriftsartikel (refereegranskat)abstract
- Aims. We compare surface maps of the chemically peculiar star HD50773 produced with a Bayesian technique and based on high quality CoRoT photometry with those derived from rotation phase resolved spectropolarimetry. The goal is to investigate the correlation of surface brightness with surface chemical abundance distribution and the stellar magnetic surface field. Methods. The rotational period of the star was determined from a nearly 60 days long continuous light curve obtained during the initial run of CoRoT. Using a Bayesian approach to star-spot modelling, which in this work is applied for the first time for the photometric mapping of a CP star, we derived longitudes, latitudes and radii of four different spot areas. Additional parameters like stellar inclination and the spot's intensities were also determined. The CoRoT observations triggered an extensive ground-based spectroscopic and spectropolarimetric observing campaign and enabled us to obtain 19 different high resolution spectra in Stokes parameters I and V with NARVAL, ESPaDOnS, and SemelPol spectropolarimeters. Doppler and Magnetic Doppler imaging techniques allowed us to derive the magnetic field geometry of the star and the surface abundance distributions of Mg, Si, Ca, Ti, Cr, Fe, Ni, Y, and Cu. Results. We find a dominant dipolar structure of the surface magnetic field. The CoRoT light curve variations and abundances of most elements mapped are correlated with the aforementioned geometry: Cr, Fe, and Si are enhanced around the magnetic poles and coincide with the bright regions on the surface of HD50773 as predicted by our light curve synthesis and confirmed by photometric imaging.
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| 8. |
- Nesvacil, N., et al.
(författare)
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A self-consistent chemically stratified atmosphere model for the roAp star 10 Aquilae
- 2013
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 552, s. A28-
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Tidskriftsartikel (refereegranskat)abstract
- Context. Chemically peculiar A-type (Ap) stars are a subgroup of the CP2 stars that exhibit anomalous overabundances of numerous elements, e.g. Fe, Cr, Sr, and rare earth elements. The pulsating subgroup of Ap stars, the roAp stars, present ideal laboratories to observe and model pulsational signatures, as well as the interplay of the pulsations with strong magnetic fields and vertical abundance gradients. Aims. Based on high-resolution spectroscopic observations and observed stellar energy distributions, we construct a self-consistent model atmosphere for the roAp star 10 Aquilae (HD 176232). It accounts for modulations of the temperature-pressure structure caused by vertical abundance gradients. We demonstrate that such an analysis can be used to determine precisely the fundamental atmospheric parameters required for pulsation modelling. Methods. Average abundances were derived for 56 species. For Mg, Si, Ca, Cr, Fe, Co, Sr, Pr, and Nd, vertical stratification profiles were empirically derived using the DDAFIT minimisation routine together with the magnetic spectrum synthesis code SYNTHMAG. Model atmospheres were computed with the LLMODELS code, which accounts for the individual abundances and stratification of chemical elements. Results. For the final model atmosphere, T-eff = 7550 K and log (g) = 3.8 were adopted. While Mg, Si, Co, and Cr exhibit steep abundance gradients, Ca, Fe, and Sr showed much wider abundance gradients between log tau(5000) = -1.5 and 0.5. Elements Mg and Co were found to be the least stratified, while Ca and Sr showed strong depth variations in abundance of up to approximate to 6 dex.
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| 9. |
- Nesvacil, N., et al.
(författare)
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Element stratification in roAp stars 10 Aquilae (HD 176232)
- 2008
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Ingår i: Contributions of the Astronomical Observatory Skalnaté Pleso. - 1335-1842. ; 38:2, s. 329-334
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Tidskriftsartikel (refereegranskat)abstract
- We present the results of our analysis of the vertical element stratification in the atmospheres of 9 roAp stars. Using high resolution observations (R approximate to 100000) obtained with the ESO-VLT spectrograph UVES and state of the art model atmosphere and spectral synthesis codes, we analysed the inhomogeneous vertical distribution of Mg, Si, Ca, Cr, Fe and Sr in 10 Aquilae (HD 176232) and Fe stratification in the whole sample. We present the derived vertical abundance map of 10 Aquilae's atmosphere and compare our findings with Fe stratification profiles of all roAp stars.
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| 10. |
- Obbrugger, M., et al.
(författare)
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First results on the multi-element Doppler imaging of the CP star HD 3980
- 2008
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Ingår i: Contributions of the Astronomical Observatory Skalnate Pleso. - 1335-1842. ; 38:2, s. 347-352
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Tidskriftsartikel (refereegranskat)abstract
- We present the first results of an ongoing analysis of the inhomogeneous elemental surface distribution in the lithium-rich magnetic Ap star HD 3980. To derive surface maps for Fe, Pr, Li, Gd and Cr the Doppler imaging inversion code INVERS12 was applied. For this work high resolution time-series observations obtained with the VLT Ultraviolet and Visual Echelle Spectrograph (UVES) were used.
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