Nitrogen enrichment, boron depletion and magnetic  fields in slowly-rotating B-type dwarfs

Morel, Thierry; Hubrig, S.; Briquet, Maryline

doi:10.1051/0004-6361:20078999

Cited by 118 publications

(179 citation statements)

References 67 publications

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“…While ζ Cas was found to be nitrogen rich, the analysis of HD 85953 revealed a normal chemical composition. For the candidate SPB star HD 169467, with a measured longitudinal magnetic field B z hydr = −233±43 G, Zboril & North (1999) determined LTE abundance ratios of C, N, and O ([N/C] and [N/O]) that are typical of those found by Morel et al (2008) in their sample of magnetic slowly-rotating B-type dwarfs, indicating that this star is N-rich too. Boesgaard & Heacox (1978) used Copernicus observations to determine the boron abundance in a sample of B-type stars and found HD 169467 to be boron depleted, assigning the same boron abundance to this star as to the magnetic SPB star ζ Cas.…”

Section: Resultsmentioning

confidence: 94%

“…Recently, Morel et al (2006Morel et al ( , 2008 performed an NLTE abundance analysis of a sample of slowly rotating earlytype B dwarfs with detected weak magnetic fields. The studied sample included, among other stars, also a number of SPB and β Cephei stars for which we carried out a magnetic field survey in recent years.…”

Section: Resultsmentioning

confidence: 99%

“…The presence of a magnetic field in these stars might play an important role to explain these physical characteristics. To search for the presence of possible differences in fundamental parameters between pulsating and non-pulsating stars we also selected seven non-pulsating normal early to mid B-type stars including the nitrogen-rich B star HD 52089 recently studied by Morel et al (2008).…”

Section: The Sample Of Pulsating Starsmentioning

confidence: 99%

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New magnetic field measurements of β Cephei stars and slowly pulsating B stars

Hubrig¹,

Briquet²,

Cat³

et al. 2009

Astron Nachr

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We present the results of the continuation of our magnetic survey with FORS 1 at the VLT of a sample of B-type stars consisting of confirmed or candidate β Cephei stars and Slowly Pulsating B (hereafter SPB) stars, along with a small number of normal B-type stars. A weak mean longitudinal magnetic field of the order of a few hundred Gauss was detected in three β Cephei stars and two stars suspected to be β Cephei stars, in five SPB stars and eight stars suspected to be SPB stars. Additionally, a longitudinal magnetic field at a level larger than 3σ has been diagnosed in two normal B-type stars, the nitrogen-rich early B-type star HD 52089 and in the B5 IV star HD 153716. Roughly one third of β Cephei stars have detected magnetic fields: Out of 13 β Cephei stars studied to date with FORS 1, four stars possess weak magnetic fields, and out of the sample of six suspected β Cephei stars two show a weak magnetic field. The fraction of magnetic SPBs and candidate SPBs is found to be higher: Roughly half of the 34 SPB stars have been found to be magnetic and among the 16 candidate SPBs eight stars possess magnetic fields. In an attempt to understand why only a fraction of pulsating stars exhibit magnetic fields, we studied the position of magnetic and non-magnetic pulsating stars in the H-R diagram. We find that their domains in the H-R diagram largely overlap, and no clear picture emerges as to the possible evolution of the magnetic field across the main sequence. It is possible that stronger fields tend to be found in stars with lower pulsating frequencies and smaller pulsating amplitudes. A somewhat similar trend is found if we consider a correlation between the field strength and the v sin i-values, i.e. stronger magnetic fields tend to be found in more slowly rotating stars.

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Section: Resultsmentioning

confidence: 94%

Section: Resultsmentioning

confidence: 99%

Section: The Sample Of Pulsating Starsmentioning

confidence: 99%

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New magnetic field measurements of β Cephei stars and slowly pulsating B stars

Hubrig¹,

Briquet²,

Cat³

et al. 2009

Astron Nachr

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“…In this paper, we present results for main-sequence O stars. Our sample is smaller than those of Morel et al (2008) or Hunter et al (2008) but it allowed us to identify some trends, and extend their work to the most massive stars. Figure 6 shows the nitrogen surface abundance as a function of rotational velocity.…”

Section: Chemical Evolution and Rotationmentioning

confidence: 99%

A quantitative study of O stars in NGC 2244 and the Monoceros OB2 association

Martins

Mahy

Hillier

et al. 2012

A&A

103

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Aims. Our goal is to determine the stellar and wind properties of seven O stars in the cluster NGC 2244 and three O stars in the OB association Mon OB2. These properties give us insight into the mass loss rates of O stars. They allow us to both check the validity of rotational mixing in massive stars and to better understand the effects of the ionizing flux and wind mechanical energy release on the surrounding interstellar medium and its influence on triggered star formation. Methods. We collected optical and UV spectra of the target stars that we analyzed by means of atmosphere models computed with the code CMFGEN. The spectra of binary stars were disentangled and the components studied separately. Results. All stars have an evolutionary age less than 5 million years, with the most massive stars being among the youngest. Nitrogen surface abundances show no clear relation with projected rotational velocities. Binaries and single stars show the same range of enrichment. This is attributed to the youth and/or wide separation of the binary systems in which the components have not (yet) experienced strong interaction. A clear trend toward greater enrichment in higher luminosity objects is observed, consistent with what evolutionary models with rotation predict for a population of O stars at any given age. We confirm the weakness of winds in late O dwarfs. In general, mass loss rates derived from UV lines are lower than mass loss rates obtained from Hα. The UV mass loss rates are even lower than the single-line driving limit in the latest type dwarfs. These issues are discussed in the context of the structure of massive stars winds. The evolutionary and spectroscopic masses are in agreement above 25 M , but the uncertainties are large. Below this threshold, the few late-type O stars studied here indicate that the mass discrepancy still seems to hold.

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“…This study was based on Kurucz (1993) atmosphere models and non-LTE modelling techniques, as well as a time series analysis of high-quality spectroscopic data assembled for these stars primarily for spectroscopic mode identification. In a follow-up study, Morel et al (2008) increased the sample to 20 stars. These studies unexpectedly discovered a population of nitrogen-rich and boron-depleted, yet intrinsically slowly-rotating early-B stars (see also, e.g., Gies & Lambert 1992).…”

Section: Introductionmentioning

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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Nitrogen enrichment, boron depletion and magnetic fields in slowly-rotating B-type dwarfs

Cited by 118 publications

References 67 publications

New magnetic field measurements of β Cephei stars and slowly pulsating B stars

New magnetic field measurements of β Cephei stars and slowly pulsating B stars

A quantitative study of O stars in NGC 2244 and the Monoceros OB2 association

Abundance analysis of prime B-type targets for asteroseismology

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