Effective temperatures of magnetic chemically peculiar stars from full spectral energy distributions

Lipski, Ł.; Stępień, K.

doi:10.1111/j.1365-2966.2008.12856.x

Cited by 18 publications

(38 citation statements)

References 41 publications

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“…The most recent effective temperature estimate for HD 125248, T eff = 9500 K, was obtained by Lipski & Stȩpień (2008) from a fit of metal-enhanced model atmospheres to the observed spectral energy distributions (SED) in the ultraviolet (UV) and optical regions. However, the authors assumed a surface gravity log g = 4.0 and an increased metallicity by 0.5 dex relative to the Sun, which raises some concern about the accuracy of the study because the phase averaged mean spectrum shows metal lines that are significantly stronger than what was assumed by Lipski & Stȩpień (2008).…”

Section: Fundamental Parameters Of Hd 125248mentioning

confidence: 99%

Magnetic Doppler imaging of the chemically peculiar star HD 125248

Rusomarov

Kochukhov

Ryabchikova

et al. 2016

A&A

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Context. Intermediate-mass, chemically peculiar stars with strong magnetic fields provide an excellent opportunity to study the topology of their surface magnetic fields and the interplay between magnetic geometries and abundance inhomogeneities in the atmospheres of these stars. Aims. We reconstruct detailed maps of the surface magnetic field and abundance distributions for the magnetic Ap star HD 125248. Methods. We performed the analysis based on phase-resolved, four Stokes parameter spectropolarimetric observations obtained with the HARPSpol instrument. These data were interpreted with the help of magnetic Doppler imaging techniques and model atmospheres taking the effects of strong magnetic fields and nonsolar chemical composition into account. Results. We improved the atmospheric parameters of the star, T eff = 9850 ± 250 K and log g = 4.05 ± 0.10. We performed detailed abundance analysis, which confirmed that HD 125248 has abundances typical of other Ap stars, and discovered significant vertical stratification effects for the Fe ii and Cr ii ions. We computed LSD Stokes profiles using several line masks corresponding to Fepeak and rare earth elements, and studied their behavior with rotational phase. Combining previous longitudinal field measurements with our own observations, we improved the rotational period of the star P rot = 9.29558 ± 0.00006 d. Magnetic Doppler imaging of HD 125248 showed that its magnetic field is mostly poloidal and quasi-dipolar with two large spots of different polarity and field strength. The chemical maps of Fe, Cr, Ce, Nd, Gd, and Ti show abundance contrasts of 0.9-3.5 dex. Among these elements, the Fe abundance map does not show high-contrast features. Cr is overabundant around the negative magnetic pole and has 3.5 dex abundance range. The rare earth elements and Ti are overabundant near the positive magnetic pole. Conclusions. The magnetic field of HD 125248 has strong deviations from the classical oblique dipole field geometry. A comparison of the magnetic field topology of HD 125248 with the results derived for other stars using four Stokes magnetic Doppler imaging suggests evidence that the field topology becomes simpler with increasing age. The abundance maps show weak correlation with magnetic field geometry, but they do not agree with the theoretical atomic diffusion calculations, which predict element accumulation in the horizontal field regions.

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Section: Fundamental Parameters Of Hd 125248mentioning

confidence: 99%

Magnetic Doppler imaging of the chemically peculiar star HD 125248

Rusomarov

Kochukhov

Ryabchikova

et al. 2016

A&A

View full text Add to dashboard Cite

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“…They showed that the UV data require T eff ≈ 10 750 K, which is about 1000 K cooler than T eff inferred from the optical spectrophotometry. The final T eff = 11 250 ± 500 K recommended by Lipski & Stȩpień (2008) is formally not different from the temperature adopted by , but has a much larger uncertainty reflecting the difficulty of fitting the stellar spectrum in a broad wavelength region.…”

Section: Physical Properties Of α 2 Cvnmentioning

confidence: 99%

“…For the temperature T eff = 11 600 ± 500 K and the bolometric correction BC = −0.42 measured by Lipski & Stȩpień (2008) we obtain L = 101 ± 12 L and R = 2.49 ± 0.26 R assuming M bol = 4.75 for the Sun (Bessell 2000) and using an uncertainty of 0.1 for the bolometric correction of α 2 CVn. Then, employing this stellar luminosity and temperature we can determine the evolutionary state of α 2 CVn by comparing its observed position in the H-R diagram with the predictions of the theoretical evolutionary tracks by Schaller et al (1992) and Schaerer et al (1993).…”

Section: Physical Properties Of α 2 Cvnmentioning

confidence: 99%

“…We found that the atlas9 models computed with 10 times solar metal abundance provide a satisfactory fit to observations for T eff = 11 600 ± 150 K and log g = 3.9 ± 0.1. Subsequently Lipski & Stȩpień (2008) used the same model atmosphere code to fit the optical spectral energy distribution simultaneously with the UV fluxes recorded by the IUE satellite. They showed that the UV data require T eff ≈ 10 750 K, which is about 1000 K cooler than T eff inferred from the optical spectrophotometry.…”

Section: Physical Properties Of α 2 Cvnmentioning

confidence: 99%

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Magnetic Doppler imaging ofα²Canum Venaticorum in all four Stokes parameters

Kochukhov¹,

Wade

2010

A&A

114

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Context. Strong organized magnetic fields have been studied in the upper main sequence chemically peculiar stars for more than half a century. However, only recently have observational methods and numerical techniques become sufficiently mature to allow us to record and interpret high-resolution four Stokes parameter spectra, leading to the first assumption-free magnetic field models of these stars. Aims. Here we present a detailed magnetic Doppler imaging analysis of the spectropolarimetric observations of the prototypical magnetic Ap star α 2 CVn. This is the second star for which the magnetic field topology and horizontal chemical abundance inhomogeneities have been inferred directly from phase-resolved observations of line profiles in all four Stokes parameters, free from the traditional assumption of a low-order multipolar field geometry.Methods. We interpret the rotational modulation of the circular and linear polarization profiles of the strong Fe ii and Cr ii lines in the spectra of α 2 CVn recorded with the MuSiCoS spectropolarimeter. The surface abundance distributions of the two chemical elements and a full vector map of the stellar magnetic field are reconstructed in a self-consistent inversion using our state-of-the-art magnetic Doppler imaging code Invers10. Results. We succeeded in reproducing most of the details of the available spectropolarimetric observations of α 2 CVn with a magnetic map which combines a global dipolar-like field topology with localized spots of higher field intensity. We demonstrate that these small-scale magnetic structures are inevitably required to fit the linear polarization spectra; however, their presence cannot be inferred from the Stokes I and V observations alone. We also found high-contrast surface distributions of Fe and Cr, with both elements showing abundance minima in the region of weaker and topologically simpler magnetic field. Conclusions. Our magnetic Doppler imaging analysis of α 2 CVn and previous results for 53 Cam support the view that the upper main sequence stars can harbour fairly complex surface magnetic fields which resemble oblique dipoles only at the largest spatial scales. Spectra in all four Stokes parameters are absolutely essential to unveil and meaningfully characterize this field complexity in Ap stars. We therefore suggest that understanding magnetism of stars in other parts of the H-R diagram is similarly incomplete without investigation of their linear polarization spectra.

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“…Previous attempts to model the spectrophotometry of magnetic Ap stars (Adelman & Rayle 2000;Lipski & Stȩpień 2008) could utilize only the information about the shape of the energy distribution because observations were often given in relative flux units. Furthermore, the stellar angular diameters were generally unknown for Ap stars and had to be treated as free parameters.…”

Section: Spectral Energy Distribution and Photometrymentioning

confidence: 99%

A self-consistent empirical model atmosphere, abundance and stratification analysis of the benchmark roAp starα Circini

Kochukhov¹,

Shulyak

Ryabchikova

2009

A&A

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Context. Chemically peculiar (CP) stars are unique natural laboratories for the investigation of the microscopic diffusion processes of chemical elements. The element segregation under the influence of gravity and radiation pressure leads to the appearance of strong abundance gradients in the atmospheres of CP stars. Consequently, the atmospheric temperature-pressure structure of these objects could deviate significantly from the atmospheres of normal stars with homogeneous abundances. Aims. In this study we performed a self-consistent, empirical model atmosphere study of the brightest rapidly oscillating Ap star α Cir. We account for chemical stratification in the model atmosphere calculations and assess the importance of non-uniform vertical element distribution on the model structure, energy distribution and hydrogen line profiles.Methods. For the chemical stratification analysis we use the ddafit minimization tool in combination with a magnetic spectrum synthesis code. The model atmospheres with inhomogeneous vertical distributions of elements are calculated with the llmodels stellar model atmosphere code. Results. Based on an iterative procedure of the chemical abundance analysis of 52 ions of 35 elements, stratification modeling of 4 elements (Si, Ca, Cr and Fe) and subsequent re-calculations of the atmospheric structure, we derived a new model atmosphere of α Cir which is consistent with the inferred atmospheric chemistry of the star. We find T eff = 7500 K, log g = 4.1, and demonstrate that chemical stratification has a noticeable impact on the model structure and modifies the formation of the hydrogen Balmer lines. At the same time, the energy distribution appears to be less sensitive to the presence of large abundance gradients. Conclusions. Our spectroscopically determined T eff of α Cir agrees with the fundamental effective temperature of this star. This shows that temperatures inferred in detailed spectroscopic analyses of cool magnetic CP stars are not affected by a large systematic bias.

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Effective temperatures of magnetic chemically peculiar stars from full spectral energy distributions

Cited by 18 publications

References 41 publications

Magnetic Doppler imaging of the chemically peculiar star HD 125248

Magnetic Doppler imaging of the chemically peculiar star HD 125248

Magnetic Doppler imaging ofα²Canum Venaticorum in all four Stokes parameters

A self-consistent empirical model atmosphere, abundance and stratification analysis of the benchmark roAp starα Circini

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Effective temperatures of magnetic chemically peculiar stars from full spectral energy distributions

Cited by 18 publications

References 41 publications

Magnetic Doppler imaging of the chemically peculiar star HD 125248

Magnetic Doppler imaging of the chemically peculiar star HD 125248

Magnetic Doppler imaging ofα2Canum Venaticorum in all four Stokes parameters

A self-consistent empirical model atmosphere, abundance and stratification analysis of the benchmark roAp starα Circini

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Resources

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Magnetic Doppler imaging ofα²Canum Venaticorum in all four Stokes parameters