Theoretical Lifetimes and Oscillator Strengths in Ce II. Application to the Chemical Composition of the Sun

We have derived abundances of 33 elements and upper limits for 6 additional elements for the metal-poor ([Fe/H] = −2.42) turn-off star HE 0338−3945 from high-quality VLT-UVES spectra. The star is heavily enriched, by about a factor of 100 relative to iron and the Sun, in the heavy s-elements (Ba, La, ...). It is also heavily enriched in Eu, which is generally considered an r-element, and in other similar elements. It is less enriched, by about a factor of 10, in the lighter s-elements (Sr, Y and Zr). C is also strongly enhanced and, to a somewhat lesser degree, N and O. These abundance estimates are subject to severe uncertainties due to NLTE and thermal inhomogeneities which are not taken into detailed consideration. However, an interesting result, which is most probably robust in spite of these uncertainties, emerges: the abundances derived for this star are very similar to those of other stars with an overall enhancement of all elements beyond the iron peak. We have defined criteria for this class of stars, r + s stars, and discuss nine different scenarios to explain their origin. None of these explanations is found to be entirely convincing. The most plausible hypotheses involve a binary system in which the primary component goes through its giant branch and asymptotic giant branch phases and produces CNO and s-elements which are dumped onto the observed star. Whether the r-element Eu is produced by supernovae before the star was formed (perhaps triggering the formation of a low-mass binary), by a companion as it explodes as a supernova (possibly triggered by mass transfer), or whether it is possibly produced in a high-neutron-density version of the s-process is still unclear. Several suggestions are made on how to clarify this situation.Key words. stars: population ii -stars: fundamental parameters -stars: abundances -Galaxy: halo -Galaxy: abundances -Galaxy: evolution IntroductionElements with atomic numbers Z > 30 are believed to be almost exclusively synthesized in neutron-capture (n-capture) reactions. In the most metal-poor stars the overall abundance of these elements varies from star to star, by more than a factor of 100 at a given metallicity (McWilliam et al. 1995;Ryan et al. 1996). Also, the different abundance ratios vary, e.g. the Ba/Eu ratio tends to decline with decreasing [Fe/H]

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“…The f -values were gathered from various sources, Palmeri et al (2000), Sneden et al (1996), Gratton & Sneden (1994), and VALD.…”

Section: Continuedmentioning

confidence: 99%

The Hamburg/ESO R-process enhanced star survey (HERES)

Jonsell¹,

Barklem²,

Gustafsson³

et al. 2006

A&A

163

277

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“…In a few cases, however, oscillator strengths were corrected as is described by Bikmaev et al (2002). One important aspect of the present abundance analysis was the Pr-Nd anomaly and we therefore used the latest data on rare-earth elements published by Palmeri et al (2000) for Ce , Bord (2000) for Nd , and Bord (private communication) for Pr .…”

Section: Abundance Determinationmentioning

confidence: 99%

The spectroscopic signature of roAp stars

Ryabchikova¹,

Nesvacil

Weiß³

et al. 2004

A&A

116

162

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Abstract.To reliably determine the spectroscopic signature of rapidly oscillating chemically peculiar (roAp) stars it is also necessary to investigate a sample of non pulsating chemically peculiar (noAp) as well as presumably "normal" stars. We describe in this study the sample of spectroscopically investigated stars and comment on the techniques used for the analysis. In particular we discuss ionization disequilibria of rare earths in roAp stars that distinguish them from noAp stars. In the light of the recently discovered pulsation of β CrB we see arguments that all magnetic CP2 stars up to a transition temperature of about 8100 K may be pulsating.

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“…New experimental oscillator strengths and hfs constants were used for La ii (Lawler et al 2001a), Ce ii (Palmeri et al 2000;Zhang et al 2001), and Eu ii lines (Lawler et al 2001b). Two weak lines of Nd iii λλ 5102, 5295, which are the strongest lines in the Nd iii spectrum, were identified in HD 32115.…”

Section: La To Eumentioning

confidence: 99%

Abundance analysis of two late A-type stars HD 32115 and HD 37594

Bikmaev

Ryabchikova

Bruntt

et al. 2002

A&A

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Abstract.We have performed abundance analysis of two slowly rotating, late A-type stars, HD 32115 (HR 1613) and HD 37594 (HR 1940), based on obtained echelle spectra covering the spectral range 4000-9850Å. These spectra allowed us to identify an extensive line list for 31 chemical elements, the most complete to date for A-type stars. Two approaches to abundance analysis were used, namely a "manual" (interactive) and a semi-automatic procedure for comparison of synthetic and observed spectra and equivalent widths. For some elements non-LTE (NLTE) calculations were carried out and the corresponding corrections have been applied. The abundance pattern of HD 32115 was found to be very close to the solar abundance pattern, and thus may be used as an abundance standard for chemical composition studies in middle and late A stars. Further, its Hα line profile shows no coreto-wing anomaly like that found for cool Ap stars and therefore also may be used as a standard in comparative studies of the atmospheric structures of cool, slowly rotating Ap stars. HD 37594 shows a metal deficiency at the level of −0.3 dex for most elements and triangle-like cores of spectral lines. This star most probably belongs to the δ Sct group.

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Theoretical Lifetimes and Oscillator Strengths in Ce II. Application to the Chemical Composition of the Sun

Cited by 71 publications

References 32 publications

The Hamburg/ESO R-process enhanced star survey (HERES)

The Hamburg/ESO R-process enhanced star survey (HERES)

The spectroscopic signature of roAp stars

Abundance analysis of two late A-type stars HD 32115 and HD 37594

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