Isotopic anomaly and stratification of Ca in magnetic Ap stars

Ryabchikova, T. A.; Kochukhov, O.; Bagnulo, S.

doi:10.1051/0004-6361:20077834

Cited by 62 publications

(84 citation statements)

References 55 publications

(72 reference statements)

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“…Reduction of the UVES spectra was performed with the automatic pipeline (Ballester et al 2000). The reduction process was described in more detail by Kochukhov et al (2006) and Ryabchikova et al (2008).…”

Section: Observationsmentioning

confidence: 99%

“…However, they did not carry out a stratification analysis but assumed a chemically-homogeneous atmosphere both for the line formation and for model atmosphere calculation. On the other hand, Ryabchikova et al (2008) presented an analysis of the Ca stratification in α Cir based on the model parameters from Kupka et al (1996) and neglecting the influence of chemical gradients on the model structure.…”

Section: Introductionmentioning

confidence: 99%

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A self-consistent empirical model atmosphere, abundance and stratification analysis of the benchmark roAp starα Circini

Kochukhov¹,

Shulyak

Ryabchikova

2009

A&A

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Context. Chemically peculiar (CP) stars are unique natural laboratories for the investigation of the microscopic diffusion processes of chemical elements. The element segregation under the influence of gravity and radiation pressure leads to the appearance of strong abundance gradients in the atmospheres of CP stars. Consequently, the atmospheric temperature-pressure structure of these objects could deviate significantly from the atmospheres of normal stars with homogeneous abundances. Aims. In this study we performed a self-consistent, empirical model atmosphere study of the brightest rapidly oscillating Ap star α Cir. We account for chemical stratification in the model atmosphere calculations and assess the importance of non-uniform vertical element distribution on the model structure, energy distribution and hydrogen line profiles.Methods. For the chemical stratification analysis we use the ddafit minimization tool in combination with a magnetic spectrum synthesis code. The model atmospheres with inhomogeneous vertical distributions of elements are calculated with the llmodels stellar model atmosphere code. Results. Based on an iterative procedure of the chemical abundance analysis of 52 ions of 35 elements, stratification modeling of 4 elements (Si, Ca, Cr and Fe) and subsequent re-calculations of the atmospheric structure, we derived a new model atmosphere of α Cir which is consistent with the inferred atmospheric chemistry of the star. We find T eff = 7500 K, log g = 4.1, and demonstrate that chemical stratification has a noticeable impact on the model structure and modifies the formation of the hydrogen Balmer lines. At the same time, the energy distribution appears to be less sensitive to the presence of large abundance gradients. Conclusions. Our spectroscopically determined T eff of α Cir agrees with the fundamental effective temperature of this star. This shows that temperatures inferred in detailed spectroscopic analyses of cool magnetic CP stars are not affected by a large systematic bias.

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Section: Observationsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

A self-consistent empirical model atmosphere, abundance and stratification analysis of the benchmark roAp starα Circini

Kochukhov¹,

Shulyak

Ryabchikova

2009

A&A

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“…Its light curve displays a small amplitude variation (0.07 mag in V), and it is classified as an α 2 CVn type variable, its variability being caused by the rotation of an inhomogeneous stellar surface. Its measured value of v sin i is 10 km s −1 (Ryabchikova et al 2008), which we verified by performing a synthetic spectrum analysis of UVES and CRIRES data. The optical spectrum displays a richness caused by the rare earth elements, which appears clearly evident at NIR wavelengths as broad but shallow features.…”

Section: Hd 118022 (O Vir) A1pmentioning

confidence: 98%

Crires-Pop

Lebzelter

Seifahrt

Uttenthaler

et al. 2012

A&A

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Context. New instrumental capabilities and the wealth of astrophysical information extractable from the near-infrared wavelength region have led to a growing interest in the field of high resolution spectroscopy at 1-5 μm. Aims. We aim to provide a library of observed high-resolution and high signal-to-noise-ratio near-infrared spectra of stars of various types throughout the Hertzsprung-Russell diagram. This is needed for the exploration of spectral features in this wavelength range and for comparison of reference targets with observations and models. Methods. High quality spectra were obtained using the CRIRES near-infrared spectrograph at ESO's VLT covering the range from 0.97 μm to 5.3 μm at high spectral resolution. Accurate wavelength calibration and correction for telluric lines were performed by fitting synthetic transmission spectra for the Earth's atmosphere to each spectrum individually. Results. We describe the observational strategy and the current status and content of the library which includes 13 objects. The first examples of finally reduced spectra are presented. This publication will serve as a reference paper to introduce the library to the community and explore the extensive amount of material.

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“…Neodymium is strongly enhanced in the uppermost atmospheric layers according to Paper I. Ryabchikova et al (2008) and demonstrated that Ca, Si, Cr, Fe, Sr, and Ba are concentrated in deep atmospheric layers. One believes that radiatively driven diffusion is one of the main processes responsible for these inhomogeneities.…”

Section: Programs and Model Atmospheresmentioning

confidence: 99%

Non-LTE line formation for Pr ii and Pr iii in A and Ap stars

Mashonkina¹,

Ryabchikova

Ryabtsev

et al. 2008

A&A

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Aims. Non-local thermodynamical equilibrium (non-LTE) line formation for singly-ionized and doubly-ionized praseodymium is considered for a range of effective temperatures between 7250 K and 9500 K. We evaluate the influence of departures from LTE on Pr abundance determinations and determine a distribution of the Pr abundance in the atmosphere of the roAp star HD 24 712 from a non-LTE analysis of the Pr ii and Pr iii lines. Methods. A comprehensive model atom for Pr ii/iii is presented based on the measured and the predicted energy levels, in total, 6708 levels of Pr ii and Pr iii and the ground state of Pr iv. Calculations of the Pr ii energy levels and oscillator strengths for the transitions in Pr ii and Pr iii are described.Results. The dependence of non-LTE effects on the atmospheric parameters is discussed. At T eff ≥ 8000 K, departures from LTE lead to the overionization of Pr ii and, therefore, to systematically depleted total absorption in the line and positive abundance corrections. At the lower temperatures, different lines of Pr ii may be either weakened or amplified depending on the line strength. The non-LTE effects strengthen the Pr iii lines and lead to negative abundance corrections. Non-LTE corrections grow with effective temperature for the Pr ii lines, and, in contrast, they decline for the Pr iii lines. The Pr ii/iii model atom is applied to determine the Pr abundance in the atmosphere of the roAp star HD 24 712 from the lines of two ionization stages. In the chemically uniform atmosphere with [Pr/H] = 3, the departures from LTE may explain only a small part (approximately 0.3 dex) of the difference between the LTE abundances derived from the Pr ii and Pr iii lines ( 2 dex). We find that the lines of both ionization stages are fitted for the vertical distribution of praseodymium, where the Pr enriched layer with [Pr/H] ≥ 4 exists in the outer atmosphere at log τ 5000 < −4. The departures from LTE for Pr ii/iii are strong in the stratified atmosphere and have the opposite sign for the Pr ii and Pr iii lines. The praseodymium stratification analysis of roAp stars has to be performed based on non-LTE line formation. Using the revised partition function of Pr ii and experimental transition probabilities, we determine the solar non-LTE abundance to be log (Pr/H) = −11.15 ± 0.08.

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Isotopic anomaly and stratification of Ca in magnetic Ap stars

Cited by 62 publications

References 55 publications

A self-consistent empirical model atmosphere, abundance and stratification analysis of the benchmark roAp starα Circini

A self-consistent empirical model atmosphere, abundance and stratification analysis of the benchmark roAp starα Circini

Crires-Pop

Non-LTE line formation for Pr ii and Pr iii in A and Ap stars

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