NLTE ionization equilibrium of Nd II and Nd III in cool A and Ap stars

Mashonkina, L.; Ryabchikova, T. A.; Ryabtsev, A. N.

doi:10.1051/0004-6361:20053085

Cited by 77 publications

(99 citation statements)

References 19 publications

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“…The fact that Mashonkina et al (2005Mashonkina et al ( , 2009) find important non-LTE effects in formation of lines of Pr and Nd ii and iii in magnetic Ap stars with T eff as low as 7250 K suggests that non-LTE effects in Si could potentially be important well below the conventional limit of T eff ≈ 15 000 K.…”

Section: Non-lte Effects In B-type Starsmentioning

confidence: 99%

Abundances determined using Si ii and Si iii in B-type stars: evidence for stratification

Bailey

Landstreet

2013

A&A

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Context. It is becoming clear that determination of the abundance of Si using lines of Si ii and Si iii can lead to quite discordant results in mid to late B-type stars. The difference between the Si abundances derived from the two ion states can exceed one dex in some cases. Aims. We have carried out a study intended to clarify which kinds of B stars exhibit this discrepancy, to try to identify regularities in the phenomenon, and to explore possible explanations such as abundance stratification by comparing models to observed spectra. Methods. We used spectra from the ESPaDOnS spectropolarimeter and FEROS spectrograph, supplemented with spectra from the ESO and ELODIE archives, of magnetic Bp, HgMn, and normal B-type stars ranging in effective temperature from about 10 500 to 15 000 K. Using these spectra, we derived abundances using the spectrum synthesis program zeeman, which can take the influence of magnetic fields into account. For each star, accurate abundances of Si ii, Si iii, Ti, Cr, and Fe were derived from two separate ∼100 Å windows. Si ii abundances were deduced from multiple lines, and Si iii abundances were found using λλ 4552, 4567, and 4574.Results. All magnetic Bp stars in our sample show a discordance between the derived abundances of the first and second ions of silicon, with the latter being between 0.6−1.7 dex higher. The same behaviour is observed in the non-magnetic stars but to a much smaller extent: Si iii is enhanced by between 0.3−0.8 dex compared to Si ii. We do not detect the discrepancy in three stars, HD 22 136 (normal), HD 57 608 (HgMn) and HD 27 295 (HgMn); these are the only stars in our sample for which the microturbulence parameter is significantly different from zero, and which therefore probably have convection occurring in their atmospheres. Conclusions. We find that vertical stratification of silicon in the atmospheres of B-type stars may provide an explanation of this phenomenon, but our detailed stratification models do not completely explain the discrepancies, which may, in part, be due to non-LTE effects.

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Section: Non-lte Effects In B-type Starsmentioning

confidence: 99%

Abundances determined using Si ii and Si iii in B-type stars: evidence for stratification

Bailey

Landstreet

2013

A&A

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“…Most of them come from the latest theoretical calculations performed by R. Kurucz 3 . Because of their large overabundance in atmospheres of Ap stars, rare-earth elements (REE) play an important and sometimes even dominating role in the appearance of spectroscopic features (Mashonkina et al , 2005 and can also affect the SED (Shulyak et al 2010b). Here we used the same line lists of REE elements as presented in Shulyak et al (2010b).…”

Section: Model Atmospheresmentioning

confidence: 99%

“…For Pr and Nd in γ Equ, we performed an NLTE stratification analysis as described in Mashonkina et al (2005Mashonkina et al ( , 2009) using a trial-and-error method and the observed equivalent widths of the lines of the first and second ions. In NLTE calculations magnetic field effects were roughly approximated by pseudomicroturbulent velocity individual for each line.…”

Section: Abundance and Stratification Analysismentioning

confidence: 99%

Fundamental parameters of bright Ap stars from wide-range energy distributions and advanced atmospheric models

Shulyak

Ryabchikova

Kochukhov

2013

A&A

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Aims. As a well-established procedure for the vast majority of normal main-sequence stars, determination of atmospheric and stellar parameters turns to be a challenging process in case of magnetic chemically peculiar stars. Inhomogeneous distribution of chemical elements and strong magnetic fields make most of the standard photometric and spectroscopic calibrations inapplicable for this class of stars. In this work we make use of available observed energy distributions calibrated to absolute units, stellar parallaxes, highresolution spectroscopic observations, and advanced stellar atmosphere models to derive parameters of three bright Ap stars: 33 Lib, γ Equ, and β CrB. Methods. Model atmospheres and fluxes were computed with the LLmodels code. Synth3 and Synthmag codes were used to compute profiles of individual spectral lines involved in abundance analysis. Results. For each of the stars, we construct a self-consistent atmospheric models assuming normal and depleted helium compositions and derive empirically stratification profiles of certain elements. The effective temperatures and surface gravities are found from the simultaneous fit to spectroscopic, photometric, and spectrophotometric observations calibrated to absolute units. We show that using advanced model atmospheres and accurate stellar parallaxes allows one to derive stellar radii with high accuracy, and these are consistent with those obtained from independent but more complicated interferometric observations.

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“…These data were supplemented by the transition probabilities for the observed and predicted lines of Pr ii−Pr iii ), Nd ii−Nd iii (Mashonkina et al 2005;Ryabchikova et al 2006), Eu iii (Wyart et al 2008), Tb iii and Dy iii (Ryabtsev, private communication), hereafter referred to as "ISAN data". For the latter two ions transition probability calculations were based on the extended term analysis.…”

Section: Ree Line Lists For Model Atmosphere Calculationmentioning

confidence: 99%

Realistic model atmosphere and revised abundances of the coolest Ap star HD 101065

Shulyak

Ryabchikova

Kildiyarova

et al. 2010

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Aims. Among the known Ap stars, HD 101065 is probably one of the most interesting objects, demonstrating very rich spectra of rareearth elements (REE). Strongly peculiar photometric parameters of this star can not be fully reproduced by any modern theoretical calculations, even those accounting for realistic chemistry of its atmosphere. In this study we investigate a role of missing REE line opacity and construct a self-consistent atmospheric model based on accurate abundance and chemical stratification analysis. Methods. We employed the LLmodels stellar model atmosphere code together with DDAFit and Synthmag software packages to derive homogeneous and stratified abundances for 52 chemical elements and to construct a self-consistent model of HD 101065 atmosphere. The opacity in REE lines is accounted for in details, by using up-to-date extensive theoretical calculations. Results. We show that REE elements play a key role in the radiative energy balance in the atmosphere of HD 101065, leading to the strong suppression of the Balmer jump and energy redistribution very different from that of normal stars. Introducing new line lists of REEs allowed us to reproduce, for the first time, spectral energy distribution of HD 101065 and achieve a better agreement between the unusually small observed Strömgren c 1 index and the model predictions. Using combined photometric and spectroscopic approaches and based on the iterative procedure of abundance and stratification analysis we find effective temperature of HD 101065 to be T eff = 6400 K.

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NLTE ionization equilibrium of Nd II and Nd III in cool A and Ap stars

Cited by 77 publications

References 19 publications

Abundances determined using Si ii and Si iii in B-type stars: evidence for stratification

Abundances determined using Si ii and Si iii in B-type stars: evidence for stratification

Fundamental parameters of bright Ap stars from wide-range energy distributions and advanced atmospheric models

Realistic model atmosphere and revised abundances of the coolest Ap star HD 101065

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