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, S.; Castelli, F.; Silva, G. De; González, J. F.; Momany, Y.; Netopil, M.; Moehler, S.

doi:10.1051/0004-6361/200911721

Cited by 21 publications

(19 citation statements)

References 48 publications

(65 reference statements)

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“…1 Borra et al (1983). It is however possible that Feige 86 exhibits more similarity with HgMn stars than with sdB stars, as it shows He and Hg isotopic anomalies (Hubrig et al 2009). …”

Section: Observations and Magnetic Field Measurementsmentioning

confidence: 99%

A search for magnetic fields in cool sdB stars

et al. 2012

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Hot cluster Horizontal Branch (HB) stars and field subdwarf B (sdB) stars are core helium burning stars that exhibit abundance anomalies that are believed to be due to atomic diffusion. Diffusion can be effective in these stars because they are slowly rotating. In particular, the slow rotation of the hot HB stars (T_eff > 11000K), which show abundance anomalies, contrasts with the fast rotation of the cool HB stars, where the observed abundances are consistent with those of red giants belonging to the same cluster. The reason why sdB stars and hot HB stars are rotating slowly is unknown. In order to assess the possible role of magnetic fields on abundances and rotation, we investigated the occurrence of such fields in sdB stars with T_eff < 30000K, whose temperatures overlap with those of the hot HB stars. We conclude that large-scale organised magnetic fields of kG order are not generally present in these stars but at the achieved accuracy, the possibility that they have fields of a few hundred Gauss remains open. We report the marginal detection of such a field in SB 290; further observations are needed to confirm it.Comment: 4 pages, 2 figures, 1 table, to appear in Astronomische Nachrichten, Proceedings of the 7th Potsdam Thinkshop on "Magnetic Fields in Stars and Exoplanets

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“…1 Borra et al (1983). It is however possible that Feige 86 exhibits more similarity with HgMn stars than with sdB stars, as it shows He and Hg isotopic anomalies (Hubrig et al 2009). …”

Section: Observations and Magnetic Field Measurementsmentioning

confidence: 99%

A search for magnetic fields in cool sdB stars

et al. 2012

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“…They detected vertical Fe stratification in five (and possibly seven) of these BHB stars. Isotopic anomalies have also been recently detected in BHB stars (Hubrig et al 2009).…”

Section: Introductionmentioning

confidence: 95%

Stratification of the elements in the atmospheres of blue horizontal-branch stars

Leblanc

Hui-Bon-Hoa

Khalack

2010

Monthly Notices of the Royal Astronomical Society

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Blue horizontal‐branch (BHB) stars with Teff approximately larger than 11 500 K show several observational anomalies. In globular clusters, they exhibit low rotational velocities, abundance anomalies (as compared to cluster abundances), photometric jumps and gaps and spectroscopic gravities lower than predicted by canonical models. It is commonly believed that the low rotational velocities of these stars permit atomic diffusion to be efficient in their atmosphere thereby causing the observed anomalies. Recent detections of vertical stratification of iron (and some other chemical elements) in several BHB stars concur with this framework. In this paper, improved model atmospheres that include the vertical stratification of the elements are applied to BHB stars to verify if they can explain their observational anomalies. The results from theoretical model atmospheres are consistent with the photometric jumps and gaps observed for BHB stars in globular clusters. It is found that iron stratification in the theoretical models and that obtained from observations have similar tendencies. Our results also show that the spectroscopic gravities obtained while using chemically homogeneous model atmospheres to fit observations are underestimated. These results significantly strengthen the belief that atomic diffusion is responsible for these BHB‐star anomalies.

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“…Vertical stratification of iron abundance was also detected by Khalack et al (2008) in the atmosphere of two BHB stars in the globular cluster M15 and for one star in the globular cluster M13. Furthermore, more recently, Hubrig et al (2009) have found isotopic anomalies of calcium in six BHB stars.…”

Section: Introductionmentioning

confidence: 95%

Vertical stratification of iron in atmospheres of blue horizontal-branch stars

Khalack

Leblanc

Behr

2010

Monthly Notices of the Royal Astronomical Society

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The aim of this study is to search for observational evidence of vertical iron stratification in the atmosphere of 14 blue horizontal-branch (BHB) stars. We have found from our numerical simulations that five BHB stars: B22, B186 in the globular cluster NGC 288, WF 2−820, WF 2−2692 in M13 and B203 in M15 show clear signatures of the vertical stratification of iron whose abundance increases toward the lower atmosphere. Two other BHB stars (B334 in M15 and B176 in M92) also show possible iron stratification in their atmosphere. A dependence of the slope of iron stratification on the effective temperature was also discovered. It is found that the vertical stratification of iron is strongest in BHB stars with T eff around 11 500 K. The slope of iron abundance decreases as T eff increases and becomes negligible for the BHB stars with T eff ≈ 14 000 K. These results support the hypothesis regarding the efficiency of atomic diffusion in the stellar atmospheres of BHB stars with T eff 11 500 K.

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

Cited by 21 publications

References 48 publications

A search for magnetic fields in cool sdB stars

A search for magnetic fields in cool sdB stars

Stratification of the elements in the atmospheres of blue horizontal-branch stars

Vertical stratification of iron in atmospheres of blue horizontal-branch stars

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