The Ca II infrared triplet as indicator of anomalous Ca isotopic mixture in HgMn stars

González

et al. 2010

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Context. Recent attention has been directed to abundance variations among very young stars. Aims. We perform a detailed abundance study of the Herbig Ae star HD 101412, taking advantage of its unusually sharp spectral lines. Methods. High-resolution spectra are measured for accurate wavelengths and equivalent widths. Balmer-line fits and ionization equlibria give a relation between T eff , and log(g). Abundance anomalies and uncertain reddening preclude the use of spectral type or photometry to fix T eff . Excitation temperatures are used to break the degeneracy between T eff and log(g). Results. Strong lines are subject to an anomalous saturation that cannot be removed by assuming a low microturbulence. By restricting the analysis to weak (≤20 mÅ) lines, we find consistent results for neutral and ionized species, based on a model with T eff = 8300 K, and log(g) = 3.8. The photosphere is depleted in the most refractory elements, while volatiles are normal or, in the case of nitrogen, overabundant with respect to the sun. The anomalies are unlike those of Ap or Am stars. Conclusions. We suggest the anomalous saturation of strong lines arises from heating of the upper atmospheric layers by infalling material from a disk. The overall abundance pattern may be related to those found for the λ Boo stars, though the depletions of the refractory elements are milder, more like those of Vega. However, the intermediate volatile zinc is depleted, precluding a straightforward interpretation of the abundance pattern in terms of gas-grain separation.

Section: Model Atmospheres and Spectral Calculationsmentioning

confidence: 77%

Section: Spectramentioning

confidence: 99%

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Abundances in the Herbig Ae star HD 101412

Cowley

González

et al. 2010

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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

2007

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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.

“…Such a shift, observed in numerous HgMn stars and Ap stars (Cowley et al 2007) was discovered by Castelli & Hubrig (2004b), who interpret it as due to an anomalous calcium isotopic composition. To compute the Xe ii line spectrum we derived the xenon abundance in each star from the equivalent widths of a set of unblended Xe ii lines.…”

Section: Isotopic Anomaliesmentioning

confidence: 77%

Wavelengths and oscillator strengths of Xe II from the UVES spectra of four HgMn stars

Yüce

Castelli

2011

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Aims. In spite of large overabundances of Xe ii observed in numerous mercury-manganese (HgMn) stars, Xe ii oscillator strengths are only available for a very limited number of transitions. As a consequence, several unidentified lines in the spectra of HgMn stars could be due to Xe ii. In addition, some predicted Xe ii lines are redshifted by about 0.1 Å from stellar unidentified lines, raising the question about the wavelength accuracy of the Xe ii line data available in the literature. For these reasons we investigated the Xe ii lines lying in the 3900-4521 Å, 4769-7542 Å, and 7660-8000 Å spectral ranges of four well-studied HgMn stars. Methods. We compared the Xe ii wavelengths listed in the NIST database with the position of the lines observed in the high-resolution UVES spectrum of the xenon-overabundant, slowly rotating HgMn star HR 6000, and we modified them when needed. We derived astrophysical oscillator strengths for all the Xe ii observed lines and compared them with the literature values, when available. We checked the stellar atomic data derived from HR 6000 by using them to compute synthetic spectra for three other xenon-overabundant, slowly rotating HgMn stars, HD 71066, 46 Aql, and HD 175640. In this framework, we performed a complete abundance analysis of HD 71066, while we relied on our previous works for the other stars. Results. We find that all the lines with wavelengths related to the 6d and 7s energy levels have a corresponding unidentified spectral line, blueshifted by the same quantity of about 0.1 Å in all the four stars, so that we identified these lines as coming from Xe ii and modified their NIST wavelength value according to the observed stellar value. We find that the Xe ii stellar oscillator strengths may differ from one star to another from 0.0 dex to 0.3 dex. We adopted the average of the oscillator strengths derived from the four stars as final astrophysical oscillator strength.