Model Atmospheres and Radiative Transfer in Chemically Peculiar Stars: Interpretational Significance of Non-LTE

One of the main problems in studying chemically peculiar (CP) stars is the question of the extent to which the conceptual framework of the contemporary spectroscopic diagnostics is reliable. As the first step, it should be clarified whether the traditional assumption of local thermodynamic equilibrium (LTE) provides an adequate approximation to reality, or whether a more general non-LTE approach should be employed.The period of rapid development of computational methods and extensive calculations of NLTE model atmospheres is now past its culmination point. The importance of a relevant NLTE description is viewed as unquestionable for hot stars (B and earlier). Consequently, the hot stars attract the attention of most “NLTE theoreticians,” while considerably less attention is being devoted to later types (late B and A). Moreover, the abundance anomalies found in the CP stars are no longer expected to be a spurious result of an inadequate (LTE) analysis (Cowley 1981). It is not commonly accepted that other phenomena such as diffusion, magnetic field, inhomogeneous abundance distribution, etc., are quite essential ingredients of the general atmospheric pattern of CP stars. Therefore, a large part of the astronomers investigating the CP stars now consider the NLTE effects to be rather minor perturbations of the LTE predictions.

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First detection of bromine and antimony in hot stars

Astronomy and Astrophysics ◽

10.1051/0004-6361/201832723 ◽

2018 ◽

Vol 614 ◽

pp. A96 ◽

Cited By ~ 5

Author(s):

K. Werner ◽

T. Rauch ◽

M. Knörzer ◽

J. W. Kruk

Keyword(s):

Model Atmosphere ◽

Atomic Diffusion ◽

Laboratory Measurements ◽

Solar Abundance ◽

Hot Stars ◽

Chemically Peculiar ◽

Peculiar Stars ◽

Resonance Doublet ◽

Chemically Peculiar Stars ◽

Far Ultraviolet

Bromine (Z = 35) and antimony (Z = 51) are extremely difficult to detect in stars. In very few instances, weak and mostly uncertain identifications of Br I, Br II, and Sb II in relatively cool, chemically peculiar stars were successful. Adopted solar abundance values rely on meteoritic determinations. Here, we announce the first identification of these species in far-ultraviolet spectra of hot stars (with effective temperatures of 49 500–70 000 K), namely in helium-rich (spectral type DO) white dwarfs. We identify the Br VI resonance line at 945.96 Å. A previous claim of Br detection based on this line is incorrect because its wavelength position is inaccurate by about 7 Å in atomic databases. Taking advantage of precise laboratory measurements, we identify this line as well as two other, subordinate Br VI lines. Antimony is detected by the Sb V resonance doublet at 1104.23/1225.98 Å as well as two subordinate Sb VI lines. A model-atmosphere analysis reveals strongly oversolar Br and Sb abundances that are caused by radiative-levitation dominated atomic diffusion.

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Rotation and Properties of A- and B-Type Chemically Peculiar Stars

Symposium - International Astronomical Union ◽

10.1017/s0074180900195713 ◽

2004 ◽

Vol 215 ◽

pp. 270-279 ◽

Cited By ~ 10

Author(s):

G. Mathys

Keyword(s):

Magnetic Fields ◽

Observational Data ◽

Main Sequence ◽

Slow Rotation ◽

Chemically Peculiar ◽

Peculiar Stars ◽

Different Types ◽

Abundance Anomalies ◽

Chemically Peculiar Stars ◽

Stellar Magnetic Fields

Main-sequence chemically peculiar stars of spectral types A and B, which are characterised by photospheric abundance anomalies resulting from element segregation in the stellar outer layers, rotate slower than normal stars of similar temperatures. The mechanisms by which such slow rotation is achieved are not well understood yet; different processes may be involved for different types of chemical peculiarities, including stellar magnetic fields and multiplicity. Relevant existing observational data are reviewed.

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Chemical Inhomogeneities and Pulsation

International Astronomical Union Colloquium ◽

10.1017/s0252921100016201 ◽

2002 ◽

Vol 185 ◽

pp. 257-265

Author(s):

S. Turcotte

Keyword(s):

Surface Composition ◽

Stellar Structure ◽

Dynamic Processes ◽

B Stars ◽

The Past ◽

Chemically Peculiar ◽

Peculiar Stars ◽

New Models ◽

Abundance Anomalies ◽

Chemically Peculiar Stars

AbstractMajor improvements in models of chemically peculiar stars have been achieved in the past few years. With these new models it has been possible to test quantitatively some of the processes involved in the formation of abundance anomalies and their effect on stellar structure. The models of metallic A (Am) stars have shown that a much deeper mixing has to be present to account for observed abundance anomalies. This has implications on their variability, which these models also reproduce qualitatively. These models also have implications for other chemically inhomogeneous stars such as HgMn B stars which are not known to be variable and λ Boötis stars which can be. The study of the variability of chemically inhomogeneous stars can provide unique information on the dynamic processes occurring in many types of stars in addition to modeling of the evolution of their surface composition.

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On-line database of photometric observations of magnetic chemically peculiar stars

Astronomische Nachrichten ◽

10.1002/asna.200610705 ◽

2007 ◽

Vol 328 (1) ◽

pp. 10-15 ◽

Cited By ~ 16

Author(s):

Z. Mikulášek ◽

J. Janík ◽

J. Zverko ◽

J. Žižňovský ◽

M. Zejda ◽

...

Keyword(s):

Chemically Peculiar ◽

Photometric Observations ◽

Peculiar Stars ◽

On Line ◽

Chemically Peculiar Stars

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Advanced test of the model stellar atmospheres: the nature of the light variability of magnetic chemically peculiar stars

Proceedings of the International Astronomical Union ◽

10.1017/s1743921308023181 ◽

2008 ◽

Vol 4 (S252) ◽

pp. 347-348

Author(s):

J. Krtička ◽

Z. Mikulášek ◽

J. Zverko ◽

J. Žižňovský ◽

P. Zvěřina

Keyword(s):

Chemical Elements ◽

Horizontal Distribution ◽

Stellar Atmospheres ◽

Silicon Iron ◽

Surface Distribution ◽

Chemically Peculiar ◽

Peculiar Stars ◽

Distribution Of Elements ◽

Chemically Peculiar Stars ◽

Light Variability

AbstractThe magnetic chemically peculiar stars exhibit both inhomogeneous horizontal distribution of chemical elements on their surfaces and the light variability. We show that the observed light variability of these stars can be successfully simulated using models of their stellar atmospheres and adopting the observed surface distribution of elements. The most important elements that influence the light variability are silicon, iron, and helium.

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29. Stellar Spectra

Transactions of the International Astronomical Union ◽

10.1017/s0251107x00004739 ◽

1982 ◽

Vol 18 (1) ◽

pp. 343-360 ◽

Cited By ~ 1

Author(s):

W.K. Bonsack

Keyword(s):

Stellar Evolution ◽

Working Group ◽

Main Sequence ◽

Symbiotic Stars ◽

Be Stars ◽

Stellar Spectra ◽

Chemically Peculiar ◽

Peculiar Stars ◽

Chemically Peculiar Stars ◽

Ap Stars

During the interval covered by this report, Commission 29 has sponsored or cosponsored the following IAU meetings: Symposium 98 on “Be Stars,” Munich, FRG, April 1981; Colloquium 59, “Effects of Mass-Loss on Stellar Evolution,” Trieste, Italy, September 1980; and Colloquim 70, “The Nature of Symbiotic Stars,” Haute-Provence, France, August 1981. In addition, Commission 29, through its Working Group on Ap Stars, collaborated in the organization of the 23rd Liege International Astrophysical Symposium on Upper Main-Sequence Chemically Peculiar Stars. Several IAU symposia and colloquia proposed for 1982 and 1983 are also cosponsored by Commission 29.

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K2 space photometry reveals rotational modulation and stellar pulsations in chemically peculiar A and B stars

Astronomy and Astrophysics ◽

10.1051/0004-6361/201833037 ◽

2018 ◽

Vol 616 ◽

pp. A77 ◽

Cited By ~ 17

Author(s):

D. M. Bowman ◽

B. Buysschaert ◽

C. Neiner ◽

P. I. Pápics ◽

M. E. Oksala ◽

...

Keyword(s):

Magnetic Field ◽

Large Scale ◽

Intrinsic Variability ◽

B Stars ◽

Pulsating Stars ◽

Chemically Peculiar ◽

Large Scale Magnetic Field ◽

Peculiar Stars ◽

Show Evidence ◽

Chemically Peculiar Stars

Context. The physics of magnetic hot stars and how a large-scale magnetic field affects their interior properties is largely unknown. Few studies have combined high-quality observations and modelling of magnetic pulsating stars, known as magneto-asteroseismology, primarily because of the dearth of detected pulsations in stars with a confirmed and well-characterised large-scale magnetic field. Aims. We aim to characterise observational signatures of rotation and pulsation in chemically peculiar candidate magnetic stars using photometry from the K2 space mission. Thus, we identify the best candidate targets for ground-based, optical spectropolarimetric follow-up observations to confirm the presence of a large-scale magnetic field. Methods. We employed customised reduction and detrending tools to process the K2 photometry into optimised light curves for a variability analysis. We searched for the periodic photometric signatures of rotational modulation caused by surface abundance inhomogeneities in 56 chemically peculiar A and B stars. Furthermore, we searched for intrinsic variability caused by pulsations (coherent or otherwise) in the amplitude spectra of these stars. Results. The rotation periods of 38 chemically peculiar stars are determined, 16 of which are the first determination of the rotation period in the literature. We confirm the discovery of high-overtone roAp pulsation modes in HD 177765 and find an additional 3 Ap and Bp stars that show evidence of high-overtone pressure modes found in roAp stars in the form of possible Nyquist alias frequencies in their amplitude spectra. Furthermore, we find 6 chemically peculiar stars that show evidence of intrinsic variability caused by gravity or pressure pulsation modes. Conclusions. The discovery of pulsations in a non-negligible fraction of chemically peculiar stars make these stars high-priority targets for spectropolarimetric campaigns to confirm the presence of their expected large-scale magnetic field. The ultimate goal is to perform magneto-asteroseismology and probe the interior physics of magnetic pulsating stars.

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