Carbon abundance and the N/C ratio in atmospheres of A-, F- and G-type supergiants and bright giants

Lyubimkov, L. S.; Lambert, David L.; Коротин, С. А.; Rachkovskaya, T. M.; Poklad, D. B.

doi:10.1093/mnras/stu2299

Cited by 32 publications

(37 citation statements)

References 31 publications

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“…For example all enhancements are less than those predicted for v o ≈ 400 km s −1 . Other recent studies such as those by Lyubimkov et al (2015) of A-, F-, and G-type supergiants in our Galaxy, have also shown good agreement with rotational stellar models with initial rotational velocities of 0−300 km s −1 .…”

Section: Nitrogen Abundances and Atmospheric Parameterssupporting

confidence: 86%

“…For example, an analysis of A-, F-, and G-type Galactic supergiants by Lyubimkov et al (2015) found both an underabundance of carbon together with an anticorrelation between the carbon and nitrogen abundances. These were consistent with mixing between the stellar core and surface during either a main sequence (MS) and/or the first dredge-up phase.…”

Section: Element Abundancesmentioning

confidence: 99%

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The VLT-FLAMES Tarantula Survey

McEvoy

Dufton

Evans

et al. 2015

A&A

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Context. Model atmosphere analyses have been previously undertaken for both Galactic and extragalactic B-type supergiants. By contrast, little attention has been given to a comparison of the properties of single supergiants and those that are members of multiple systems. Aims. Atmospheric parameters and nitrogen abundances have been estimated for all the B-type supergiants identified in the VLT-FLAMES Tarantula survey. These include both single targets and binary candidates. The results have been analysed to investigate the role of binarity in the evolutionary history of supergiants.Methods.  non-local thermodynamic equilibrium (LTE) model atmosphere calculations have been used to determine atmospheric parameters and nitrogen abundances for 34 single and 18 binary supergiants. Effective temperatures were deduced using the silicon balance technique, complemented by the helium ionisation in the hotter spectra. Surface gravities were estimated using Balmer line profiles and microturbulent velocities deduced using the silicon spectrum. Nitrogen abundances or upper limits were estimated from the N  spectrum. The effects of a flux contribution from an unseen secondary were considered for the binary sample. Results. We present the first systematic study of the incidence of binarity for a sample of B-type supergiants across the theoretical terminal age main sequence (TAMS). To account for the distribution of effective temperatures of the B-type supergiants it may be necessary to extend the TAMS to lower temperatures. This is also consistent with the derived distribution of mass discrepancies, projected rotational velocities and nitrogen abundances, provided that stars cooler than this temperature are post-red supergiant objects. For all the supergiants in the Tarantula and in a previous FLAMES survey, the majority have small projected rotational velocities. The distribution peaks at about 50 km s −1 with 65% in the range 30 km s −1 ≤ v e sin i ≤ 60 km s −1 . About ten per cent have larger v e sin i (≥100 km s −1 ), but surprisingly these show little or no nitrogen enhancement. All the cooler supergiants have low projected rotational velocities of ≤70 km s −1 and high nitrogen abundance estimates, implying that either bi-stability braking or evolution on a blue loop may be important. Additionally, there is a lack of cooler binaries, possibly reflecting the small sample sizes. Single-star evolutionary models, which include rotation, can account for all of the nitrogen enhancement in both the single and binary samples. The detailed distribution of nitrogen abundances in the single and binary samples may be different, possibly reflecting differences in their evolutionary history. Conclusions. The first comparative study of single and binary B-type supergiants has revealed that the main sequence may be significantly wider than previously assumed, extending to T eff = 20 000 K. Some marginal differences in single and binary atmospheric parameters and abundances have been identified, possibly implying non-stand...

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Section: Nitrogen Abundances and Atmospheric Parameterssupporting

confidence: 86%

Section: Element Abundancesmentioning

confidence: 99%

The VLT-FLAMES Tarantula Survey

McEvoy

Dufton

Evans

et al. 2015

A&A

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“…Hayek et al (2011) updated the Collet et al (2007) Thus, the discrepancy between the C I and CH-based abundances found by Tomkin et al (1992) in the classical 1D analysis is expected to be larger in 3D. The NLTE methods for C I were developed by Vernazza et al (1981), Shchukina & Shcherbina (1990), Stuerenburg & Holweger (1990), Takeda (1992), Przybilla et al (2001), Fabbian et al (2006), and Lyubimkov et al (2015). Stuerenburg & Holweger (1990) showed that NLTE removes a discrepancy between visible and near-IR lines of C I in the Sun, while the difference in LTE abundances between individual lines can be up to 0.37 dex, for example between C I 9111Å and 5380Å.…”

Section: Introductionmentioning

confidence: 99%

“…The Lyubimkov et al (2015) studied the NLTE effects for C I in the galactic A-, F-and G-type supergiants and bright giants.…”

Section: Introductionmentioning

confidence: 99%

Carbon abundances of reference late-type stars from 1D analysis of atomic C i and molecular CH lines

Alexeeva

Mashonkina

2015

Mon. Not. R. Astron. Soc.

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A comprehensive model atom was constructed for C I using the most up-to-date atomic data. We evaluated non-local thermodynamical equilibrium (NLTE) line formation for neutral carbon in classical 1D models representing atmospheres of late-type stars, where carbon abundance varies from solar value down to [C/H] = −3. NLTE leads to stronger C I lines compared with their LTE strength and negative NLTE abundance corrections, ∆ NLTE . The deviations from LTE are large for the strong lines in the infrared (IR), with ∆ NLTE = −0.10 dex to −0.45 dex depending on stellar parameters, and they are minor for the weak lines in the visible spectral range, with |∆ NLTE | 0.03 dex. The NLTE abundance corrections were found to be dependent of the carbon abundance in the model. As the first application of the treated model atom, carbon NLTE abundances were determined for the Sun and eight late-type stars with well-determined stellar parameters that cover the −2.56 [Fe/H] −1.02 metallicity range. Consistent abundances from the visible and IR lines were found for the Sun and the most metal-rich star of our sample, when applying a scaling factor of S H = 0.3 to the Drawinian rates of C+H collisions. Carbon abundances were also derived from the molecular CH lines and, for each star, they agree with that from the atomic C I lines. We present the NLTE abundance corrections for lines of C I in the grid of model atmospheres applicable to the carbon-enhanced (CEMP) stars.

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“…Is there such accordance in the case of AFG supergiants and bright giants? In order to answer this question, it would be useful to remember the above-mentioned N vs C anticorrelation in these stars obtained by Lyubimkov et al (2015) (see Fig.12 there). Like the present paper, a comparison between the observed and computed relations has been implemented there for the same two phases: post-MS and post-FDU.…”

Section: Discussionmentioning

confidence: 99%

Oxygen abundance and the N/C versus N/O relation for AFG supergiants and bright giants

Lyubimkov

Коротин

Lambert

2019

Monthly Notices of the Royal Astronomical Society

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Non-LTE analysis (LTE is local thermodynamic equilibrium) of the oxygen abundances for 51 Galactic A-, F-and G-type supergiants and bright giants is performed. In contrast with carbon and nitrogen, oxygen does not show any significant systematic anomalies in their abundances log ε(O). There is no marked difference from the initial oxygen abundance within errors of the log ε(O) determination across the T eff interval from 4500 to 8500 K and the log g interval from 1.2 to 2.9 dex. This result agrees well with theoretical predictions for stellar models with rotation. With our new data for oxygen and our earlier non-LTE determinations of the N and C abundances for stars from the same sample, we constructed the [N/C] vs [N/O] relation for 17 stars. This relation is known to be a sensitive indicator of stellar evolution. A pronounced correlation between [N/C] vs [N/O] is found; the observed [N/C] increase from 0 to 1.6 dex is accompanied by the [N/O] increase from 0 to 0.9 dex. When comparing the observed [N/C] vs [N/O] relation with the theoretical one, we show that this relation reflects a strong dependence of the evolutionary changes in CNO abundances on the initial rotation velocities of stars. Given that the initial rotational velocities of these stars are expected to satisfy V 0 <150 km/s, it is found that they are mostly the post first dredge-up (post-FDU) objects. It is important that just such initial velocities V 0 are typical for about 80 % of stars in question (i.e. for stars with masses 4-19 M ⊙ ). A constancy of the total C+N+O abundance during stellar evolution is confirmed. The mean value log ε(C+N+O)=8.97±0.08 found for AFG supergiants and bright giants seems to be very close to the initial value 8.92 (the Sun) or 8.94 (the unevolved B-type MS stars).

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Carbon abundance and the N/C ratio in atmospheres of A-, F- and G-type supergiants and bright giants

Cited by 32 publications

References 31 publications

The VLT-FLAMES Tarantula Survey

The VLT-FLAMES Tarantula Survey

Carbon abundances of reference late-type stars from 1D analysis of atomic C i and molecular CH lines

Oxygen abundance and the N/C versus N/O relation for AFG supergiants and bright giants

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