Model atmospheres of chemically peculiar stars

Shulyak, D.; Ryabchikova, T. A.; Mashonkina, L.; Kochukhov, O.

doi:10.1051/0004-6361/200911623

Cited by 47 publications

(98 citation statements)

References 42 publications

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“…The limb-darkened angular diameters we derived from our interferometric measurements on one side (0.335 ± 0.009 mas), and from the SED fit on the other side (0.339 mas), agree closely. In addition, the limbdarkened angular diameter and the radius that we derived from our VEGA data are identical to those computed with the selfconsistent stratified model developed by Shulyak et al (2009). By fitting the spectral energy distribution of HD 24712 with their model, which is clearly better suited to these peculiar stars than a standard model such as that of Kurucz, the authors derived an Fig.…”

Section: Discussionsupporting

confidence: 71%

“…This can lead to vertical and horizontal microscopic diffusion of the chemical elements and abnormal surface layers (Stift & Alecian 2012), which might generate systematic errors in the determination of stellar luminosities and effective temperatures by spectrometric and/or photometric techniques (Matthews et al 1999). Moreover, Shulyak et al (2009) have shown that stratification of chemical elements implies significant changes in the structure of the atmosphere model. This means that it is mandatory to determine accurate fundamental parameters by a method as independent as possible of an atmosphere model to test non-adiabatic pulsation models.…”

Section: Introductionmentioning

confidence: 99%

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The fundamental parameters of the roAp star HD 24712

Perraut

Brandão

Cunha

et al. 2016

A&A

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Context. There is still a debate about the nature of the mechanism that causes the pulsation excitation of the rapidly oscillating Ap stars that oscillate above the highest theoretically acoustic frequency. HD 24712 is a good test case for such a study because it is bright, its parallax accurately determined, and its frequency spectrum is well known. Aims. Visible long-baseline interferometry is a unique technique for measuring accurate angular diameters of targets as small as the brightest roAp stars, and thus estimating accurate radii by a method as independent as possible of atmosphere models. Methods. We used the visible spectrograph VEGA at the CHARA long-baseline optical array to observe HD 24712, and we derived its limb-darkened diameter. We also estimated its bolometric flux from spectroscopic data in the literature and determined its radius, luminosity, and effective temperature. Results. We determined a limb-darkened angular diameter of 0.335 ± 0.009 mas for HD 24712 and derived a radius of R = 1.772 ± 0.057 R , a luminosity of L = 7.2 ± 1.8 L , and an effective temperature of T eff = 7235 ± 280 K, which is in very close agreement with the values provided by the self-consistent stratified model developed for this star. We used these fundamental parameters to set HD 24712 in the Hertzsprung-Russell diagram. Its position is marginally consistent with the region where high radial order modes are predicted to be excited by the κ-mechanism. Conclusions. We conclude that oscillations in this star are most likely not driven by the κ-mechanism.

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Section: Discussionsupporting

confidence: 71%

Section: Introductionmentioning

confidence: 99%

The fundamental parameters of the roAp star HD 24712

Perraut

Brandão

Cunha

et al. 2016

A&A

Self Cite

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“…Kochukhov et al 2006, 2009;Shulyak et al 2009;Pandey et al 2011). This group has developed refined methods of recovering the vertical distribution of several elements in a stellar atmosphere by simultaneous fits to a number of spectral lines of different strengths, excitation potentials, and ionisation states.…”

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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“…We can presently surmise that HgMn and magnetic Ap stars must be relatively quiet stars since their atmospheres seem to be stable enough to allow abundance stratifications to build up and survive for a considerable time. In addition to these rather qualitative/schematic predictions from theoretical models, observational evidence for such abundance inhomogeneities has are only available in electronic form at http://www.aanda.org accumulated over recent years (see Ryabchikova et al 2002;Ryabchikova 2005;Shulyak et al 2009). Zeeman Doppler mapping (Kochukhov et al 2004) provides simultaneous magnetic and abundance maps for several elements and indicates the richness of physical processes acting in these stars.…”

Section: Introductionmentioning

confidence: 99%

Bi-dimensional element stratifications computed for magnetic Ap star atmospheres

Alecian¹,

Stift

2010

A&A

104

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Context. Theoretical modelling of abundance stratifications and surface distributions of chemical elements in Ap stars constitutes a major challenge. The atomic diffusion model provides the most appropriate framework in which to understand these abundance anomalies.Aims. We present theoretical 2D stratifications of 16 metals in upper main sequence chemically peculiar stars, with and without magnetic fields to provide a reference point for further theoretical and observational studies. Methods. We used our code CaratStrat to compute a large grid of stratifications (equilibrium solutions in LTE) for plane-parallel T eff = 8500, 10 000, 12 000, and 14 000 K stellar atmospheres. By interpolation, we constructed bi-dimensional cuts through these stellar atmospheres, which are permeated by a dipolar magnetic field of strength 20 kG at the magnetic pole. We also provide vertical (1D) stratifications of metals in non-magnetic stars (HgMn).Results. We present a large number of 2D and 1D stratifications, mostly as online material. We discuss in detail the case of Fe for the T eff = 8500 K model in the printed version, and compare it with stratifications derived from observed spectra.

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Model atmospheres of chemically peculiar stars

Cited by 47 publications

References 42 publications

The fundamental parameters of the roAp star HD 24712

The fundamental parameters of the roAp star HD 24712

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

Bi-dimensional element stratifications computed for magnetic Ap star atmospheres

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