The spectroscopic signature of roAp stars

Ryabchikova, T. A.; Nesvacil, N.; Weiß, W. W.; Kochukhov, Oleg; Stütz, Ch.

doi:10.1051/0004-6361:20041012

Cited by 116 publications

(186 citation statements)

References 45 publications

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“…An overabundance of almost 2 dex with respect to the solar abundance is found. This result is roughly consistent with the variations of abundance with T eff found in Ap stars by Ryabchikova et al (2004).…”

Section: Chromiumsupporting

confidence: 92%

Magnetic field and atmospheric chemical abundances of the magnetic Ap star HD 318107

Bailey

Landstreet

Bagnulo³

et al. 2011

A&A

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Context.A new generation of powerful and efficient spectropolarimeters has recently been used to provide the first sample of magnetic Ap stars of accurately known ages. Modelling of these data offer the possibility of significant new insights into the physics and main sequence evolution of these remarkable stars. Aims. New spectra have been obtained with the ESPaDOnS spectropolarimeter, and are supplemented with unpolarised spectra from the ESO UVES, UVES-FLAMES, and HARPS spectrographs, of the very peculiar large-field magnetic Ap star HD 318107, a member of the open cluster NGC 6405 and thus a star with a well-determined age. The available data provide sufficient material with which to re-analyse the first-order model of the magnetic field geometry and to derive chemical abundances of Si, Ti, Fe, Nd, Pr, Mg, Cr, Mn, O, and Ca. Methods. The models were obtained using ZEEMAN, a program which synthesises spectral line profiles for stars that have magnetic fields. The magnetic field structure was modelled with a low-order colinear multipole expansion, using coefficients derived from the observed variations of the field strength with rotation phase. The abundances of several elements were determined using spectral synthesis. After experiments with a very simple model of uniform abundance on each of three rings of equal width in co-latitude and symmetric about the assumed magnetic axis, we decided to model the spectra assuming uniform abundances of each element over the stellar surface. Results. The new magnetic field measurements allow us to refine the rotation period of HD 318107 to P = 9.7088 ± 0.0007 days. Appropriate magnetic field model parameters were found that very coarsely describe the (apparently rather complex) field moment variations. Spectrum synthesis leads to the derivation of mean abundances for the elements Mg, Si, Ca, Ti, Cr, Fe, Nd, and Pr. All of these elements except for Mg and Ca are strongly overabundant compared to the solar abundance ratios. There is considerable evidence of non-uniformity, for example in the different values of B z found using lines of different elements. Conclusions. The present data set, while limited, is nevertheless sufficient to provide a useful first-order assessment of both the magnetic and surface abundance properties of HD 318107, making it one of the very few magnetic Ap stars of well-known age for which both of these properties have been studied.

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Section: Chromiumsupporting

confidence: 92%

Magnetic field and atmospheric chemical abundances of the magnetic Ap star HD 318107

Bailey

Landstreet

Bagnulo³

et al. 2011

A&A

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“…This result falls well within the range of cerium abundances found for magnetic Ap stars (Ryabchikova et al 2004), and for some HgMn stars (Adelman et al 2001a,b).…”

Section: Ce IIIsupporting

confidence: 89%

Lanthanides and other spectral oddities in a Centauri

Cowley

Hubrig

González

2010

A&A

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Context. There is considerable interest in the helium variable a Cen as a bridge between helium-weak and helium-strong CP stars.Aims. We investigate Ce iii and other possible lanthanides in the spectrum the of hottest chemically peculiar (CP) star in which these elements have been found. A Kr ii line appears within a broad absorption which we suggest may be due to a high-level transition in C ii.Methods. Wavelengths and equivalent widths are measured on high-resolution UVES spectra, analyzed, and their phase-variations investigated.Results. New, robust identifications of Ce iii and Kr ii are demonstrated. Nd iii is likely present. A broad absorption near λ4619 is present at all phases of a Cen, and in some other early B stars. Conclusions. The presence of lanthanides in a Cen strengthens the view that this star is a significant link between the cooler CP stars and the hotter helium-peculiar stars. Broad absorptions in a Cen are not well explained.

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“…This significant discrepancy between the rare-earth LTE abundances derived from two ionization stages is typically found for the roAp and cool Ap stars (the REE anomaly, see Ryabchikova et al 2004).…”

Section: The Problem Of the Pr Abundance In Hd 24 712mentioning

confidence: 92%

“…For a sample of 26 stars, Ryabchikova et al (2004) highlighted a discrepancy between the abundances derived from the lines of singly ionized and doubly ionized atoms of neodymium and praseodymium, which typically exceeded 1.5 dex in roAp stars, but was substantially smaller, if present, in non-pulsating Ap stars (see also Kato 2003 andRyabchikova et al 2006, for hotter Ap stars HD 170 973 and HD 144 897). This excludes errors in the oscillator strengths as a possible reason for the abundance difference observed in roAp stars.…”

Section: Introductionmentioning

confidence: 97%

“…Classical LTE analysis finds a strong disparity between the second and the first ions of the rare-earth elements (REE) in rapidly oscillating chemically peculiar (roAp) stars (Cowley & Bord 1998;Cowley et al 2000;Gelbmann et al 2000;Ryabchikova et al 2001;Kochukhov 2003;Ryabchikova et al 2004). For a sample of 26 stars, Ryabchikova et al (2004) highlighted a discrepancy between the abundances derived from the lines of singly ionized and doubly ionized atoms of neodymium and praseodymium, which typically exceeded 1.5 dex in roAp stars, but was substantially smaller, if present, in non-pulsating Ap stars (see also Kato 2003 andRyabchikova et al 2006, for hotter Ap stars HD 170 973 and HD 144 897).…”

Section: Introductionmentioning

confidence: 99%

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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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The spectroscopic signature of roAp stars

Cited by 116 publications

References 45 publications

Magnetic field and atmospheric chemical abundances of the magnetic Ap star HD 318107

Magnetic field and atmospheric chemical abundances of the magnetic Ap star HD 318107

Lanthanides and other spectral oddities in a Centauri

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

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