A study of rare earth elements in the atmospheres of chemically peculiar stars. Pr III and Nd III lines

Ryabchikova, T. A.; Саванов, И. С.; Malanushenko, V. P.; Kudryavtsev, D. O.

doi:10.1134/1.1369801

Cited by 41 publications

(54 citation statements)

References 16 publications

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“…Ryabchikova et al 2000, HD 122970 and 10 Aql). Moreover, the same ions can be observed in non-oscillating Ap stars and do not show the same anomaly (Ryabchikova et al 2001;Weiss et al 2000).…”

Section: Discussionmentioning

confidence: 60%

The core-wing anomaly of cool Ap stars

Cowley

Hubrig²,

Ryabchikova³

et al. 2001

A&A

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Abstract. The profiles of Hα in a number of cool Ap stars are anomalous. Broad wings, indicative of temperatures in the range 7000-8000 K end abruptly in narrow cores. The widths of these cores are compatible with those of dwarfs with temperatures of 6000 K or lower. This profile has been known for Przybylski's star, but it is seen in other cool Ap stars. The Hβ profile in several of these stars shows a similar core-wing anomaly (CWA). In Przybylski's star, the CWA is probably present at higher Balmer members. We are unable to account for these profiles within the context of LTE and normal dwarf atmospheres. We conclude that the atmospheres of these stars are not "normal". This is contrary to a notion that has long been held.

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Section: Discussionmentioning

confidence: 60%

The core-wing anomaly of cool Ap stars

Cowley

Hubrig²,

Ryabchikova³

et al. 2001

A&A

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“…Rather strong lines of iron-peak elements with low RV amplitudes in these bands decrease the net value of the RV amplitude derived by cross-correlation analysis of low resolution spectra. Weiss et al (2000) and Ryabchikova et al (2001) analysed Pr iii and Nd iii lines in the spectra of a dozen roAp and non-pulsating Ap stars and found that for roAp stars elemental abundances obtained from Pr iii and Nd iii lines are up to two orders of magnitude higher than abundances derived from the lines of singly ionized Pr and Nd. In nonpulsating Ap stars the same anomaly is marginal if present at all.…”

Section: Discussionmentioning

confidence: 99%

“…In nonpulsating Ap stars the same anomaly is marginal if present at all. Ryabchikova et al (2001) proposed that REE are concentrated in the uppermost atmospheric layers where a transition from singly to doubly ionized REE occurs due to a pressure drop. Unfortunately no quantitative diffusion calculations are available for the REE.…”

Section: Discussionmentioning

confidence: 99%

Time-resolved spectroscopy of the roAp starγEqu

Kochukhov¹,

Ryabchikova

2001

A&A

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Abstract.We report results of the spectroscopic monitoring of the roAp star γ Equ with the ESO 3.6-m telescope. During 1.5 hours of observations a series of very high-resolution and high S/N spectra was obtained for this star in the 6138-6165Å spectral region. Short exposure times allowed us to resolve changes of γ Equ line profiles due to the rapid pulsations and to follow profile variations over 5 oscillation cycles. From this unique observational material information on amplitudes and phase shifts of radial velocity (RV) variations was extracted for 29 lines of 17 individual ions. We confirmed that spectral lines of rare-earth elements (REE) have the largest pulsation amplitudes, reaching up to 0.8 km s −1 . Moreover, we detected a phase shift between RV variations of singly and doubly ionized REE, discovered significant RV shifts of weak Na i lines and analysed line profile variations of Pr iii and Nd iii spectral features. This rich observational material opens a possibility to obtain a detailed picture of the vertical stratification of chemical elements and extract the main characteristics of the pulsational mode(s). In our observations we did not find support for the existence of the unique dependence of RV amplitude on line strength suggested in earlier spectroscopic studies of roAp stars. Instead, we argue that the individuality of the variations of all ions is a result of the complex interplay between inhomogeneous vertical and horizontal distributions of chemical elements and individual pulsation modes of γ Equ. We show that the extra line broadening observed in γ Equ spectrum is most likely caused by pulsations. A detailed analysis of Pr iii and Nd iii line profile variations resulted in the estimate of = 2 or 3, m = − or − + 1 and vp ≈ 10 km s −1 for the p-mode of the main pulsation frequency.

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“…In addition to this, Wade et al (2001b) argued that most magnetic stars exhibit vertical abundance variations (chemical stratification), an idea first explored by Babel (1992). The phenomenon was further studied by Ryabchikova et al (2001), who compared the chemical abundances derived from the singlyand doubly-ionised forms of Pr and Nd in magnetic and nonmagnetic A-type stars. In pulsating ("roAp") magnetic stars, abundances derived from the second ions were found to be 1−1.7 dex larger than abundances from the first ions.…”

Section: Introductionmentioning

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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A study of rare earth elements in the atmospheres of chemically peculiar stars. Pr III and Nd III lines

Cited by 41 publications

References 16 publications

The core-wing anomaly of cool Ap stars

The core-wing anomaly of cool Ap stars

Time-resolved spectroscopy of the roAp starγEqu

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

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