Heavy calcium in CP stars

Cowley, Charles R.; Hubrig, S.; Castelli, F.; González, J. F.; Wolff, B.

doi:10.1111/j.1365-2966.2007.11719.x

Cited by 16 publications

(17 citation statements)

References 31 publications

(39 reference statements)

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“…The absence of P overabundance is unusual, but is known for several other HgMn stars with T eff similar to 66 Eri A (Adelman et al 2001), while a significant Ga overabundance is mostly inferred from the optical spectra of HgMn stars much hotter than 66 Eri A (Ryabchikova et al 1996). Thus, 66 Eri A is undoubtedly an HgMn star and was treated as such in many modern studies (Cowley et al 2007;Catanzaro & Leto 2004;Rottler & Young 2002;Woolf & Lambert 1999;Hubrig 1998). 66 Eri is also classified as "Hg" in the updated "Catalogue of Ap, HgMn and Am stars" (Renson & Manfroid 2009).…”

Section: Summary and Discussionmentioning

confidence: 99%

Chemical spots in the absence of magnetic field in the binary HgMn star 66 Eridani

Makaganiuk

Kochukhov

Piskunov

et al. 2011

A&A

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Context. According to our current understanding, a subclass of the upper main-sequence chemically peculiar stars, called mercurymanganese (HgMn), is non-magnetic. Nevertheless, chemical inhomogeneities were recently discovered on their surfaces. At the same time, no global magnetic fields stronger than 1-100 G are detected by systematic studies. Aims. The goals of our study are to search for a magnetic field in the HgMn binary system 66 Eri and to investigate chemical spots on the stellar surfaces of both components. Methods. Our analysis is based on high-quality spectropolarimetric time-series observations obtained during 10 consecutive nights with the HARPSpol instrument at the ESO 3.6-m telescope. To increase the sensitivity of the magnetic field search we employed a least-squares deconvolution (LSD). We used spectral disentangling to measure radial velocities and study the line profile variability. Chemical spot geometry was reconstructed using multi-line Doppler imaging. Results. We report a non-detection of magnetic field in 66 Eri, with error bars 10-24 G for the longitudinal field. Circular polarization profiles also do not indicate any signatures of complex surface magnetic fields. For a simple dipolar field configuration we estimated an upper limit of the polar field strength to be 60-70 G. For the HgMn component we found variability in spectral lines of Ti, Ba, Y, and Sr with the rotational period equal to the orbital one. The surface maps of these elements reconstructed with the Doppler imaging technique show a relative underabundance on the hemisphere facing the secondary component. The contrast of chemical inhomogeneities ranges from 0.4 for Ti to 0.8 for Ba.

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Section: Summary and Discussionmentioning

confidence: 99%

Chemical spots in the absence of magnetic field in the binary HgMn star 66 Eridani

Makaganiuk

Kochukhov

Piskunov

et al. 2011

A&A

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“…A vertical abundance inhomogeneous distribution was found in HgMn and in other subgroups of CP stars. The Ca stratification and isotope separation in several chemically peculiar stars has recently been investigated by Cowley et al (2007Cowley et al ( , 2009) and by Ryabchikova et al (2008) who show that heavy Ca isotopes in a few stars are most likely concentrated towards the higher atmospheric layers. No sign of an elemental vertical inhomogeneous distribution was found in any spectrum of the studied stars.…”

Section: Discussionmentioning

confidence: 99%

“…7 we present Ca isotopic shifts for Ca ii triplet lines (λ 8498, λ 8542 and λ 8662) for each BHB star versus T eff and log g. We see no indication that Ca isotopic anomalies are related to the atmospheric parameters of our stars. Recently, Cowley et al (2007) have studied a potential temperature correlation of the Ca isotopic anomaly in magnetic Ap stars and HgMn stars. They notice that there may be a weak correlation with temperature for HgMn stars in the sense that hotter stars show larger isotopic shifts.…”

Section: Isotopesmentioning

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

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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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“…The wavelength red-shift of the infrared triplet observed in several CP stars (Cowley et al 2007) was interpreted by Castelli & Hubrig (2004a) as due to a Ca isotopic composition different from the terrestrial one.…”

Section: Isotopic Anomaliesmentioning

confidence: 99%

A refined analysis of the remarkable Bp star HR 6000

Castelli

Hubrig

2007

A&A

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Aims. UVES spectra of the very young ( ∼ 10 7 years) peculiar B-type star HR 6000 were analyzed in the near-UV and visual spectral regions (3050-9460 Å) with the aim to extend to other spectral ranges the study made previously in the UV using IUE spectra. Methods. Stellar parameters T eff =12850 K, log g=4.10, and ξ=0 km s −1 , as determined from H β , H γ , H δ Balmer profiles and from the Fe i, Fe ii ionization equilibrium, were used to compute an individual abundances ATLAS12 model. We identified spectral peculiarities and obtained final stellar abundances by comparing observed and computed equivalent widths and line profiles.Results. The adopted model fails to reproduce the (b-y) and c color indices. The spectral analysis has revealed: the presence of emission lines for Mn ii, Cr ii, and Fe ii; isotopic anomalies for Hg , Ca ; the presence of interstellar lines of Na i at λλ 3302.3, 3302.9, 5890, 5896 Å, and of K i at 7665, 7699 Å; the presence of a huge quantity of unidentified lines, which we presume to be mostly due to Fe ii transitions owing to the large Fe overabundance amounting to [+0.7]. The main chemical peculiarities are an extreme overabundance of Xe, followed by those of Hg, P, Y, Mn, Fe, Be, and Ti. The most underabundant element is Si, followed by C, N, Al, S, Mg, V, Sr, Co, Cl, Sc, and Ni. The silicon underabundance [−2.9] is the lowest value for Si ever observed in any HgMn star. The observed lines of He i can not be reproduced by a single value of the He abundance, but they require values ranging from [−0.8] to [−1.6]. Furthermore, when the observed and computed wings of He i lines are fitted, the observed line cores are much weaker than the computed ones. From the present analysis we infer the presence of vertical abundance stratification for He, Mn, and possibly also P.

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Heavy calcium in CP stars

Cited by 16 publications

References 31 publications

Chemical spots in the absence of magnetic field in the binary HgMn star 66 Eridani

Chemical spots in the absence of magnetic field in the binary HgMn star 66 Eridani

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

A refined analysis of the remarkable Bp star HR 6000

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