Atomic data for opacity calculations. XIV. The beryllium sequence

Tully, J. A.; Seaton, M. J.; Berrington, K A

doi:10.1088/0953-4075/23/21/016

Cited by 145 publications

(104 citation statements)

References 49 publications

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“…Photoionization cross-sections were taken from calculations by Tully et al (1990), via TOPbase 5 , the OPACITY Project online database (Cunto & Mendoza 1992). For excited levels without available OPACITY Project data (5g 1 G, 5g 3 G, 6s 1 S, and 6g 3 G, see Table A.2), resonance-free cross-sections were used, provided in terms of the Seaton (1958) approximation with parameters from the wm-basic database.…”

Section: The Nitrogen Model Atommentioning

confidence: 99%

Nitrogen line spectroscopy of O-stars

González

Puls

Najarro

et al. 2012

A&A

101

107

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Context. Nitrogen is a key element for testing the impact of rotational mixing on evolutionary models of massive stars. Recent studies of the nitrogen surface abundance in B-type stars within the VLT-FLAMES survey of massive stars have challenged part of the corresponding predictions. To obtain a more complete picture of massive star evolution, and to allow for additional constraints, these studies need to be extended to O-stars. Aims. This is the second paper in a series aiming at the analysis of nitrogen abundances in O-type stars, to establish tighter constraints on the early evolution of massive stars. In this paper, we investigate the N ivλ4058 emission line formation, provide nitrogen abundances for a substantial O-star sample in the Large Magellanic Cloud, and compare our (preliminary) findings with recent predictions from stellar evolutionary models. Methods. Stellar and wind parameters of our sample stars were determined by line profile fitting of hydrogen, helium and nitrogen lines, exploiting the corresponding ionization equilibria. Synthetic spectra were calculated by means of the NLTE atmosphere/spectrum synthesis code fastwind, using a new nitrogen model atom. We derived nitrogen abundances for 20 O-and 5 B-stars by analyzing all nitrogen lines (from different ionization stages) present in the available optical spectra. Results. The dominating process responsible for emission at N ivλ4058 in O-stars is the strong depopulation of the lower level of the transition, which increases as a function ofṀ. Unlike the N iii triplet emission, resonance lines do not play a role for typical mass-loss rates and below. We find (almost) no problem in fitting the nitrogen lines, in particular the "f" features. Only for some objects, where lines from N iii/N iv/N v are visible in parallel, we need to opt for a compromise solution. For five objects in the early B-/late O-star domain that have been previously analyzed by different methods and model atmospheres, we derive consistent nitrogen abundances. The bulk of our sample O-stars seems to be strongly nitrogen-enriched, and a clear correlation of nitrogen and helium enrichment is found. By comparing the nitrogen abundances as a function of v sin i ("Hunter-plot") with tailored evolutionary calculations, we identify a considerable number of highly enriched objects at low rotation. Conclusions. Our findings seem to support the basic outcome of previous B-star studies within the VLT-FLAMES survey. Owing to the low initial abundance, the detection of strong nitrogen enrichment in the bulk of O-stars indicates that efficient mixing takes place already during the very early phases of stellar evolution of LMC O-stars. For tighter constraints, however, upcoming results from the VLT-FLAMES Tarantula survey need to be waited for, which will comprise a much higher number of O-stars that will be analyzed based on similar methods as presented here.

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Section: The Nitrogen Model Atommentioning

confidence: 99%

Nitrogen line spectroscopy of O-stars

González

Puls

Najarro

et al. 2012

A&A

101

107

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“…Results for the singlet ground level and, for the first time, also for the lowest lying, metastable triplet level were presented. A substantial extension of the early theoretical studies was accomplished by the work of Tully et al [11] using the non-relativistic R-matrix technique to calculate photoionization cross sections in LS -coupling for the beryllium isoelectronic sequence starting with Be and reaching up to Fe 22+ . The data obtained for different ions and especially for the beryllium sequence are available from the Opacity Project [12] and can be retrieved from the TOPBASE database (http://rxte.gsfc.nasa.gov/topbase/).…”

Section: Introductionmentioning

confidence: 99%

State-resolved valence shell photoionization of Be-like ions: experiment and theory

Müller¹,

Schippers²,

Phaneuf³

et al. 2010

J. Phys. B: At. Mol. Opt. Phys.

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Abstract. High-resolution photoionization experiments were carried out using beams of Be-like C 2+ , N 3+ , and O 4+ ions with roughly equal populations of the 1 S ground-state and the 3 P o manifold of metastable components. The energy scales of the experiments are calibrated with uncertainties of 1 to 10 meV depending on photon energy. Resolving powers beyond 20,000 were reached allowing for the separation of contributions from the individual metastable 3 P o 0 , 3 P o 1 , and 3 P o 2 states. The measured data compare favourably with semi-relativistic Breit-Pauli R-matrix calculations.

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“…The opacity calculated using the OP cross-sections for C i (Luo & Pradhan 1989), C ii (Yan & Seaton 1987) and C iii (Tully et al 1990) is greater at smaller wavelengths than the opacity computed using the old cross-sections. For C i the result is an increase in opacity of up to a factor of 10 for λ < 3300 Å.…”

Section: A2 Free-free Absorptionmentioning

confidence: 78%

LTE model atmospheres with new opacities

Behara

Jeffery

2006

A&A

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We describe an opacity sampled version of the LTE model atmosphere code sterne with revised continuous opacities. In particular, we examine the results of replacing the existing treatment of the continuous opacities which followed the method of Kurucz (1970, SAOSR, No. 309) and Peach (1970, MNRAS, 73, 1), with photoionization cross-sections from the Opacity Project and the IRON Project, and the effects of substituting an opacity distribution function method for treating the line opacities with an opacity sampling method. In studying the application of these new models to atmospheres with hydrogen-rich and extreme chemical compositions, we find the new opacity treatment increases the temperature in the line forming region by up to 3000 K for extremely hydrogen-poor stars and up to 1250 K for hydrogen-rich stars with T eff = 30 000 K and log g = 3.00. This translates into systematically cooler effective temperature measurements for these types of stars.

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Atomic data for opacity calculations. XIV. The beryllium sequence

Cited by 145 publications

References 49 publications

Nitrogen line spectroscopy of O-stars

Nitrogen line spectroscopy of O-stars

State-resolved valence shell photoionization of Be-like ions: experiment and theory

LTE model atmospheres with new opacities

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