Abundance analysis of late B stars

Hempel, M.; Holweger, H.

doi:10.1051/0004-6361:20030889

Cited by 39 publications

(47 citation statements)

References 28 publications

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“…This can be the result of a purely LTE analysis. As discussed by Hempel & Holweger (2003), the non-LTE abundances of Si in this temperature range are higher than the LTE values. The non-LTE corrections amount to about 0.2 dex, while the average Si abundance determined here is lower than the solar value by about 0.25 dex.…”

Section: Results Of Abundance Analysismentioning

confidence: 68%

“…For this reason, we did not use the O i 7771−5 Å triplet for the determination of the oxygen abundance (Paunzen et al 1999). The non-LTE effects for B-type stars are discussed in detail by Hempel & Holweger (2003). They analysed the abundances of several light elements (He, C, O, Ne, Mg, Si, Ca), Fe, and two heavy elements (Sr, Ba) in 27 bright B5−B9 main-sequence stars.…”

Section: Discussion Of Errorsmentioning

confidence: 99%

“…In these conditions, diffusion can easily occur. A significant number of late-B stars exhibit spectroscopic signatures of these microscopic transport processes (e.g., Hempel & Holweger 2003;Folsom et al 2007). The investigation of late-B star atmospheres will help us to understand these physical phenomena.…”

Section: Article Published By Edp Sciencesmentioning

confidence: 99%

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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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Section: Results Of Abundance Analysismentioning

confidence: 68%

Section: Discussion Of Errorsmentioning

confidence: 99%

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Abundance analysis of prime B-type targets for asteroseismology

Niemczura¹,

Morel²,

Aerts

2009

A&A

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“…Even for the case of the superficially "normal" stars, the elemental abundances of late-B to F stars show a range of possible abundances (Adelman & Unsuree 2007;Hempel & Holweger 2003). Adelman & Unsuree (2007) found that the abundance distribution in normal A stars overlap with those of the Am stars.…”

Section: Abundances Of Sn Stars Vs Cp Starsmentioning

confidence: 99%

“…In our sample of sn stars, three objects display abundances within this approximate range (HD 21071, HD 162586, and HD 162678). Hempel & Holweger (2003) studied 27 B stars classified as normal and detected anomalous rather than solar abundances in different elements (O, Mg, Ca, Fe, Sr, Ba). They show that the anomalies do not occur to the same extent in all stars but instead show star-to-star variations.…”

Section: Abundances Of Sn Stars Vs Cp Starsmentioning

confidence: 99%

On the nature of sn stars

Saffe

Levato

2014

A&A

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The sn stars were first discoved by Abt & Levato when studying the spectral types in different open clusters. These stars present sharp Balmer lines, sharp metallic lines (C II, Si II, Ca II, Ti II, Fe II), and broad coreless He I lines. Some of the sn stars seem to be related to CP stars. Initially Abt & Levato proposed a shell-like nature to explain the sn stars, although this scenario was subsequently questioned. There is no general agreement about their origin. We aim to derive abundances for a sample of 9 stars, including sn and non-sn stars, to determine the possible relation between sn and CP stars and compare their chemical abundances. That most sn stars belong to open clusters allows us to search for a possible relation with fundamental parameters, including the age and rotation. We also study the possible contribution of different effects to the broad He I lines observed in these stars, such as Stark broadening and the possible He-stratification. Effective temperature and gravity were estimated by Strömgren photometry and then refined by requiring ionization and excitation equilibrium of Fe lines. We derived the abundances by fitting the observed spectra with synthetic spectra using an iterative procedure with the SYNTHE and ATLAS9 codes. We derived metallic abundances of 23 different chemical elements for 9 stars and obtained low projected rotational velocities for the sn stars in our sample (v sin i up to 69 km s −1 ). We also compared 5 stars that belong to the same cluster (NGC 6475) and show that the sn characteristics appear in the 3 stars with the lower rotational velocity. However, the apparent preference of sn stars for objects with the lower v sin i values should be taken with caution due to the small number of objects studied here. We analysed the photospheric chemical composition of sn stars and show that approximately ∼40% of them display chemical peculiarities (such as He-weak and HgMn stars) within a range of temperature of 10 300 K−14 500 K. However, there are also sn stars with solar or nearly-solar (i.e. non-CP) chemical composition. We have studied the possible contribution of different processes to the broad He I lines present in the sn stars. Although NLTE effects could not be completely ruled out, it seems that NLTE is not directly related to the broad He I profiles observed in the sn stars. The broad-line He I 4026 Å is the clearest example of the sn characteristics in our sample. We succesfully fit this line in 4 out of 7 sn stars by using the appropriate Stark broadening tables, while small differences appear in the other 3 stars. Studying the plots of abundance vs. depth for the He I lines resulted in some sn stars probably being stratified in He. However, a further study of variability in the He I lines would help for determining whether a possible non-uniform He superficial distribution could also play a role in these sn stars. We conclude that the broad He I lines that characterize the sn class could be modelled (at least in some of these stars) by the usual radiati...

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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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Abundance analysis of late B stars

Cited by 39 publications

References 28 publications

Abundance analysis of prime B-type targets for asteroseismology

Abundance analysis of prime B-type targets for asteroseismology

On the nature of sn stars

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

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