Emission lines in the optical spectrum of 3 Cen A

Wahlgren, G. M.; Hubrig, S.

doi:10.1051/0004-6361:20034257

Cited by 33 publications

(59 citation statements)

References 11 publications

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“…Strong isotopic anomalies were detected for the chemical elements Ca, Pt, and Hg with patterns changing from one star to the next (Hubrig et al 1999a;Dolk et al 2003;Castelli & Hubrig 2004b;Cowley et al 2008). The presence of weak emission lines of various elements was for the first time reported by Wahlgren & Hubrig (2000). Observationally, these stars are characterized by low rotational velocities ( v sin i ≤ 29 km s −1 , Abt et al 1972).…”

Section: Introductionmentioning

confidence: 82%

Spectroscopic variability and magnetic fields of HgMn stars

et al. 2011

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The discovery of exotic abundances, chemical inhomogeneities, and weak magnetic fields on the surface of late B-type primaries in spectroscopic binaries has important implications not only for our understanding of the formation mechanisms of stars with Hg and Mn peculiarities themselves, but also for the general understanding of B-type star formation in binary systems. The origin of the abundance anomalies observed in late B-type stars with HgMn peculiarity is still poorly understood. The connection between HgMn peculiarity and membership in binary and multiple systems is supported by our observations during the last decade. The important result achieved in our studies of a large sample of HgMn stars is the finding that most HgMn stars exhibit spectral variability of various chemical elements, proving that the presence of an inhomogeneous distribution on the surface of these stars is a rather common characteristic and not a rare phenomenon. Further, in the studied systems, we found that all components are chemically peculiar with different abundance patterns. Generally, He and Si variable Bp stars possess large-scale organised magnetic fields that in many cases appear to occur essentially in the form of a single large dipole located close to the centre of the star. The presence of magnetic fields in the atmospheres of HgMn stars has been demonstrated in several studies. In addition to the measurements of longitudinal and quadratic magnetic fields, this work also showed evidence for a relative magnetic intensification of Fe II lines produced by different magnetic desaturations induced by different Zeeman-split components.

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Section: Introductionmentioning

confidence: 82%

Spectroscopic variability and magnetic fields of HgMn stars

et al. 2011

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“…They have strong magnetic fields (as the CP2 group) which produce elemental surface inhomogeneities together with photometric variations. Several objects also show emission in the optical spectral range and signs of mass loss (Wahlgren & Hubrig 2004). The percentage of detection (94%) at +10 mmag is even higher than that of the CP2 group leading to the conclusion that almost all magnetic chemically peculiar stars can be detected with the ∆a photometric system.…”

Section: Cp4 Starsmentioning

confidence: 96%

On the detection of chemically peculiar stars using $\mathsf{\Delta}$a photometry

Paunzen

Stütz

Maitzen

2005

A&A

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Abstract.We have summarized all ∆a measurements for galactic field stars (1474 objects) from the literature published over more than two decades. These measurements were, for the first time, compiled and homogeneously analyzed. The ∆a intermediate band photometric system samples the depth of the 5200 Å flux depression by comparing the flux at the center with the adjacent regions with bandwidths of 110 Å to 230 Å. Because it was slightly modified over the last three decades, we checked for systematic trends for the different measurements but found no correlations whatsoever. The ∆a photometric system is most suitable to detecting magnetic chemically peculiar (CP) stars with high efficiency, but is also capable of detecting a small percentage of non-magnetic CP objects. Furthermore, the groups of (metal-weak) λ Bootis, as well as classical Be/shell stars, can be successfully investigated. In addition, we also analyzed the behaviour of supergiants (luminosity class I and II). On the basis of apparent normal type objects, the correlation of the 3σ significance limit and the percentage of positive detection for all groups was derived. We compared the capability of the ∆a photometric system with the ∆(V1 − G) and Z indices of the Geneva 7-color system to detect peculiar objects. Both photometric systems show the same efficiency for the detection of CP and λ Bootis stars, while the indices in the Geneva system are even more efficient at detecting Be/shell objects. On the basis of this statistical analysis it is possible to derive the incidence of CP stars in galactic open cluster and extragalactic systems including the former unknown bias of undetected objects. This is especially important in order to make a sound statistical analysis of the correlation between the occurrence of these objects and astrophysical parameters such as the age, metallicity, and strength of global, as well as local, magnetic fields.

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“…Presently, explanations of this phenomenon have been put forward in the context of the non-LTE line formation (Sigut 2001) and possible fluorescence mechanisms (Wahlgren & Hubrig 2000). No obvious correlations have been noted for emission in terms of stellar parameters of studied B-type stars.…”

Section: Emissionsmentioning

confidence: 99%

A high-resolution study of isotopic composition and chemical abundances of blue horizontal branch stars in the globular clusters NGC 6397 and NGC 6752

Hubrig

Castelli

Silva

et al. 2009

A&A

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Aims. Large abundance anomalies have been previously detected in Horizontal Branch B-type stars. It has been suggested that at T eff > 11 000 K the stellar atmospheres become susceptible to diffusion effects and thus develop surface abundances similar to those that appear in the main-sequence, chemically peculiar group of A and B-type stars. We present the first high-resolution study of isotopic anomalies and chemical abundances in six Horizontal Branch B-type stars in globular clusters NGC 6397 and NGC 6752 and compare them to those observed in HgMn stars. Methods. We obtained high-resolution (up to R ∼ 115 000) UVES spectra of a representative sample of six B-type stars (T183, T191, T193, B652, B2151, B2206) with sharp spectral lines (v sin i ≤ 10 km s −1 ). The stars T183 and B2151 were observed on two consecutive nights to examine potential spectrum variability. A detailed spectrum analysis was done relying on Kurucz ATLAS9 and ATLAS12 models. The spectra were analysed using the SYNTHE code to generate synthetic spectra. Results. It is the first time an abundance analysis is performed for all elements for which spectral lines were detected in UVES spectra of Horizontal Branch B-type stars. Our study of these stars revealed no signs of He isotopic anomalies, which would produce a 3 He/ 4 He ratio different from the solar one. The isotopic anomaly of Ca is detected in all six studied stars. The chemical abundance analysis reveals an overabundance over the solar values of P, Ti, Mn, Fe, and Y and an overabundance over the cluster metallicity of Mg, Ca, and Cr. This behaviour is very similar in all six stars of both clusters with a few exceptions: the Na abundance is larger by more than 1.4 dex than the cluster metallicity in B652, and by more than 0.8 dex greater than the cluster metallicity in B2206; the Co abundance is 1.0 dex over the solar abundance for T191, while Zr is overabundant over the solar abundance by 0.4 dex in B2206. No lines of Hg or other heavy elements were observed in the spectra. Weak emission lines of Ti ii, similar to those frequently observed in HgMn stars have been discovered in one Horizontal Branch B-type star T191. Furthermore, we detected a radial velocity change of 0.9 km s −1 from one night to the next for T183 and 0.4 km s −1 for B2151. Further high-resolution observations are needed to examine whether both stars are spectroscopic binaries.

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Emission lines in the optical spectrum of 3 Cen A

Cited by 33 publications

References 11 publications

Spectroscopic variability and magnetic fields of HgMn stars

Spectroscopic variability and magnetic fields of HgMn stars

On the detection of chemically peculiar stars using $\mathsf{\Delta}$a photometry

A high-resolution study of isotopic composition and chemical abundances of blue horizontal branch stars in the globular clusters NGC 6397 and NGC 6752

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