The calcium isotopic anomaly in magnetic CP stars

Cowley, C. R.; Hubrig, S.

doi:10.1051/0004-6361:200500013

Cited by 19 publications

(22 citation statements)

References 18 publications

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“…Castelli & Hubrig (2004) first announced detection of 48 Ca in several HgMn (CP3) stars. Cowley & Hubrig (2005) subsequently found a similar effect in magnetic Ap (CP2) stars. The shifts appear to vary from those indicating nearly pure 48 Ca to a virtual terrestrial mix (nearly pure 40 Ca).…”

Section: Introductionmentioning

confidence: 64%

Heavy calcium in CP stars

Cowley

Hubrig

Castelli

et al. 2007

Monthly Notices of the Royal Astronomical Society

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Large wavelength shifts of infrared triplet lines of Ca ii have been observed in the spectra of HgMn and magnetic Ap stars. They have been attributed to the heavy calcium isotopes, including 48Ca. One member of the triplet, λ8542, had been either unavailable, or of poor quality in earlier spectra. The present material shows conclusively that the stellar λ8542 shifts are consistent with an interpretation in terms of 48Ca. We find no relation between isotopic shifts of the Ca ii triplet lines, and those of Hg iiλ3984. There is a marginal indication that the shifts are anticorrelated with the surface field strengths of the magnetic stars. We see sparse evidence for 48Ca in other chemically peculiar stars, for example, Am stars, metal‐poor stars or chemically peculiar red giants. However, the sample is still very small, and the wavelengths of all three triplet lines, including those in the Sun, show slight positive shifts with respect to terrestrial positions. Some profiles of the Ca ii infrared triplet in the magnetic stars show extensive wings beyond a well‐defined core. We can obtain reasonable fits to these profiles using a stratified calcium abundance similar to that used by previous workers. There is no indication that either the stratification or the Zeeman effect significantly disturbs the measurement of isotope shifts.

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Section: Introductionmentioning

confidence: 64%

Heavy calcium in CP stars

Cowley

Hubrig

Castelli

et al. 2007

Monthly Notices of the Royal Astronomical Society

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“…One immediately notices that while the line wings are explained by our calculations, the line core cannot be fitted with the terrestrial Ca isotopic mixture. Cowley & Hubrig (2005) showed that the red-shift of the Ca IR line core arises due to the heavy Ca isotopes and claimed that "in extreme cases the dominant isotope is the exotic 48 Ca".…”

Section: The Ca Isotopic Anomalymentioning

confidence: 99%

“…In addition to remarkable diffusion signatures, recently another Ca anomaly was detected, first in the spectra of the Hg-Mn stars by Castelli & Hubrig (2004) and then in Ap stars by Cowley & Hubrig (2005).…”

Section: Introductionmentioning

confidence: 99%

Isotopic anomaly and stratification of Ca in magnetic Ap stars

Ryabchikova

Kochukhov

Bagnulo

2008

A&A

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Aims. We have completed an accurate investigation of the Ca isotopic composition and stratification in the atmospheres of 23 magnetic chemically peculiar (Ap) stars of different temperature and magnetic field strength. Methods. With the UVES spectrograph at the 8 m ESO VLT, we have obtained high-resolution spectra of Ap stars in the wavelength range 3000-10 000 Å. Using a detailed spectrum synthesis calculations, we have reproduced a variety of Ca lines in the optical and ultraviolet spectral regions, inferring the overall vertical distribution of Ca abundance, and have deduced the relative isotopic composition and its dependence on height using the profile of the IR-triplet Ca ii line at λ8498 Å.Results. In 22 out of 23 studied stars, we found that Ca is strongly stratified, being usually overabundant by 1.0-1.5 dex below log τ 5000 ≈ −1, and strongly depleted above log τ 5000 = −1.5. The IR-triplet Ca ii line at λ8498 Å reveals a significant contribution of the heavy isotopes 46 Ca and 48 Ca, which represent less than 1 % of the terrestrial Ca isotopic mixture. We confirm our previous finding that the presence of heavy Ca isotopes is generally anticorrelated with the magnetic field strength. Moreover, we discover that in Ap stars with relatively small surface magnetic fields (≤4-5 kG), the light isotope 40 Ca is concentrated close to the photosphere, while the heavy isotopes are dominant in the outer atmospheric layers. This vertical isotopic separation, observed for the first time for any metal in a stellar atmosphere, disappears in stars with magnetic field strength above 6-7 kG. Conclusions. We suggest that the overall Ca stratification and depth-dependent isotopic anomaly observed in Ap stars may be attributed to a combined action of the radiatively-driven diffusion and light-induced drift.

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“…Calcium is an element of considerable interest for many of the cases mentioned above. For example the isotope shift information in the 3d 2 D J → 4p 2 P J infrared triplet [11] led to the discovery of an anomalous isotopic composition in mercury-manganese (HgMn) stars, in which the isotopic Ca ratio in the stellar atmosphere is dominated by 48 Ca [12,13]. Isotope shifts in other calcium transitions have been studied, e.g., to extract nuclear charge radii along the long chain of isotopes [14,15,16,17] or to perform ultra-trace analysis using isotope selective resonance ionization [18].…”

Section: Introductionmentioning

confidence: 99%

Unexpectedly large difference of the electron density at the nucleus in the $$ 4p\, ^2{\mathrm {P}}_{{1}/{2},{3}/{2}}$$ 4 p 2 P 1 / 2 , 3 / 2 fine-structure doublet of Ca $$^+$$ +

et al. 2016

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We measured the isotope shift in the 2 S1 /2 → 2 P3 /2 (D2) transition in singly-ionized calcium ions using photon recoil spectroscopy. The high accuracy of the technique enables us to resolve the difference between the isotope shifts of this transition to the previously measured isotopic shifts of the 2 S1 /2 → 2 P1 /2 (D1) line. This so-called splitting isotope shift is extracted and exhibits a clear signature of field shift contributions. From the data we were able to extract the small difference of the field shift coefficient and mass shifts between the two transitions with high accuracy. This J-dependence is of relativistic origin and can be used to benchmark atomic structure calculations. As a first step, we use several ab initio atomic structure calculation methods to provide more accurate values for the field shift constants and their ratio. Remarkably, the high-accuracy value for the ratio of the field shift constants extracted from the experimental data is larger than all available theoretical predictions.

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The calcium isotopic anomaly in magnetic CP stars

Cited by 19 publications

References 18 publications

Heavy calcium in CP stars

Heavy calcium in CP stars

Isotopic anomaly and stratification of Ca in magnetic Ap stars

Unexpectedly large difference of the electron density at the nucleus in the $$ 4p\, ^2{\mathrm {P}}_{{1}/{2},{3}/{2}}$$ 4 p 2 P 1 / 2 , 3 / 2 fine-structure doublet of Ca $$^+$$ +

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