Catalogue of averaged stellar effective magnetic fields

Бычков, В. Д.; Бычкова, Л. В.; Madej, J.

doi:10.1051/0004-6361:20030741

Cited by 85 publications

(120 citation statements)

References 155 publications

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“…Another possibility might be that HD 202850 is a Si star, though its magnetic field does not seem particularly strong (but exceptions are still known, e.g. V 828 Her B9sp, EE Dra B9, Bychkov et al 2003). A detailed abundance analysis may help to solve this puzzling feature.…”

Section: Micro-turbulent Velocities and Si Abundancesmentioning

confidence: 99%

Bright OB stars in the Galaxy

Маркова¹,

Puls²

2007

A&A

185

264

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Context. B-type supergiants represent an important phase in the evolution of massive stars. Reliable estimates of their stellar and wind parameters, however, are scarce, especially at mid and late spectral subtypes. Aims. We apply the NLTE atmosphere code FASTWIND to perform a spectroscopic study of a small sample of Galactic B-supergiants from B0 to B9. By means of the resulting data and incorporating additional datasets from alternative studies, we investigate the properties of OB-supergiants and compare our findings with theoretical predictions. Methods. Stellar and wind parameters of our sample stars are determined by line profile fitting, based on synthetic profiles, a Fourier technique to investigate the individual contributions of stellar rotation and "macro-turbulence" and an adequate approach to determine the Si abundances in parallel with micro-turbulent velocities. Results. Due to the combined effects of line-and wind-blanketing, the temperature scale of Galactic B-supergiants needs to be revised downward, by 10 to 20%, the latter value being appropriate for stronger winds. Compared to theoretical predictions, the wind properties of OB-supergiants indicate a number of discrepancies. In fair accordance with recent results, our sample indicates a gradual decrease in v ∞ over the bi-stability region, where the limits of this region are located at lower T eff than those predicted. Introducing a distance-independent quantity Q related to wind-strength, we show that this quantity is a well defined, monotonically increasing function of T eff outside this region. Inside and from hot to cool,Ṁ changes by a factor (in between 0.4 and 2.5) which is much smaller than the predicted factor of 5. Conclusions. The decrease in v ∞ over the bi-stability region is not over-compensated by an increase ofṀ , as frequently argued, provided that wind-clumping properties on both sides of this region do not differ substantially.

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Section: Micro-turbulent Velocities and Si Abundancesmentioning

confidence: 99%

Bright OB stars in the Galaxy

Маркова¹,

Puls²

2007

A&A

185

264

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“…Indeed, IQ Aur is extreme for an A0p star; as a main-sequence star it would be of spectral type mid-B with its B − V = −0.16. The adopted basic stellar data for IQ Aur and α 2 CVn as compiled from Bohlender et al (1993), Bychkov et al (2003), Kochukhov & Bagnulo (2006) and Kochukhov & Wade (2010) are summarized in Table 1.…”

Section: The Targets α 2 Cvn and Iq Aurmentioning

confidence: 99%

“…The comparison sample is specified in Table 4; some of these objects have already been presented, albeit with a different focus in Stelzer et al (2006); Czesla & Schmitt (2007). Most stars are Si-stars, but some of the hotter ones are also classified as He-weak, moreover all stars have detected magnetic fields of a few hundred G up to several kG (Bychkov et al 2003). The used stellar data are again taken from Kochukhov & Bagnulo (2006), additional values are from Landstreet et al (2007).…”

Section: X-rays From Similar Ap/bp Starsmentioning

confidence: 99%

New X-ray observations of IQ Aurigae andα² Canum Venaticorum

Robrade

Schmitt

2011

A&A

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Aims. We re-examine the scenario of X-ray emission from magnetically confined/channeled wind shocks (MCWS) for Ap/Bp stars, a model originally developed to explain the ROSAT detection of the A0p star IQ Aur. Methods. We present new X-ray observations of the A0p stars α 2 CVn (Chandra) and IQ Aur (XMM-Newton) and discuss our findings in the context of X-ray generating mechanisms of magnetic, chemically peculiar intermediate mass stars. Results. The X-ray luminosities of IQ Aur with log L X = 29.6 erg s −1 and α 2 CVn with log L X 26.0 erg s −1 differ by at least three orders of magnitude, although both are A0p stars. By studying a sample of comparison stars, we find that X-ray emission is preferably generated by more massive objects such as IQ Aur. Besides a strong, cool plasma component, significant amounts of hot (>10 MK) plasma are present during the quasi-quiescent phase of IQ Aur; moreover, diagnostics of the UV sensitive f /i line ratio in He-like O vii triplet point to X-ray emitting regions well above the stellar surface of IQ Aur. In addition we detect a large flare from IQ Aur with temperatures up to ∼100 MK and a peak X-ray luminosity of log L X ≈ 31.5 erg s −1 . The flare, showing a fast rise and e-folding decay time of less than half an hour, originates in a fairly compact structure and is accompanied by a significant metallicity increase. The X-ray properties of IQ Aur cannot be described by wind shocks only and require the presence of magnetic reconnection. This is most evident in the, to our knowledge, first X-ray flare reported from an A0p star. Conclusions. Our study indicates that the occurrence the of X-ray emission in A0p stars generated by magnetically channeled wind shocks depends on stellar properties such as luminosity, which promote a high mass loss rate, whereas magnetic field configuration and transient phenomena refine their appearance. While we cannot rule out unknown close companions, the X-ray emission from IQ Aur can be described consistently in the MCWS scenario, in which the very strong magnetic confinement of the stellar wind has led to the build-up of a rigidly rotating disk around the star, where magnetic reconnection and centrifugal breakout events occur.

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“…Adelman et al (2004) analysed the lines of very heavy elements (Pt, Au, Hg, Tl, and Bi) in the UV spectra of 21 Aql. Bychkov et al (2003) classified this star as a chemically peculiar silicon star. Ryabchikova (2005) considered the temperature behaviour of elemental abundances in the atmosphere of magnetic peculiar stars, including 21 Aql.…”

Section: Also Foundmentioning

confidence: 99%

Abundance analysis of prime B-type targets for asteroseismology

Niemczura¹,

Morel²,

Aerts

2009

A&A

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Aims. The main goal of the ground-based seismology support program for the CoRoT mission was to obtain photometric and spectroscopic data for stars in the fields monitored by the satellite. These ground-based observations were collected in the GAUDI archive. High-resolution spectra of more than 200 B-type stars are available in this database, and about 45% of them is analysed here. Methods. To derive the effective temperature of the stars, we used photometric indices. Surface gravities were obtained by comparing observed and theoretical Balmer line profiles. To determine the chemical abundances and rotational velocities, we used a spectrum synthesis method, which consisted of comparing the observed spectrum with theoretical ones based on the assumption of LTE. Results. Atmospheric parameters, chemical abundances, and rotational velocities were determined for 89 late-B stars. The dominant species in their spectra are iron-peak elements. The average Fe abundance is 7.24 ± 0.45 dex. The average rotational velocity is 126 km s −1 , but there are 13 and 20 stars with low and moderate V sin i values, respectively. The analysis of this sample of 89 late B-type stars reveals many chemically peculiar (CP) stars. Some of them were previously known, but at least 9 new CP candidates, among which at least two HgMn stars, are identified in our study. These CP stars as a group exhibit V sin i values lower than the stars with normal surface chemical composition.

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Catalogue of averaged stellar effective magnetic fields

Cited by 85 publications

References 155 publications

Bright OB stars in the Galaxy

Bright OB stars in the Galaxy

New X-ray observations of IQ Aurigae andα² Canum Venaticorum

Abundance analysis of prime B-type targets for asteroseismology

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Catalogue of averaged stellar effective magnetic fields

Cited by 85 publications

References 155 publications

Bright OB stars in the Galaxy

Bright OB stars in the Galaxy

New X-ray observations of IQ Aurigae andα2 Canum Venaticorum

Abundance analysis of prime B-type targets for asteroseismology

Contact Info

Product

Resources

About

New X-ray observations of IQ Aurigae andα² Canum Venaticorum