Abstract:Abstract. High-resolution UCLES/AAT spectra are presented for nine B-type supergiants in the SMC, chosen on the basis that they may show varying amounts of nuclear-synthetically processed material mixed to their surface. These spectra have been analysed using a new grid of approximately 12 000 non-LTE line blanketed model atmospheres to estimate atmospheric parameters and chemical composition. The abundance estimates for O, Mg and Si are in excellent agreement with those deduced from other studies, whil… Show more
“…Details of the methods adopted can be found in Hunter et al (2007), while a more detailed discussion of the grids can be found in Ryans et al (2003), Dufton et al (2005) 2 . Here only a brief summary will be given, with further details available as discussed above.…”
Section: Methodsmentioning
confidence: 99%
“…The validity of such an approach was investigated by Dufton et al (2005), who analysed the spectra of B-type Ia supergiants in the SMC using the current grid and also theoretical spectra generated by the code (Santolaya-Rey et al 1997;Puls et al 2005), that incorporates wind effects. Dufton et al (2005) found excellent agreement in the atmospheric parameters estimated from the two methods. Effective temperature estimates agreed to within typically 500 K, logarithmic gravities to 0.1 dex and microturbulent velocities to 2 km s −1 .…”
Section: Methodsmentioning
confidence: 99%
“…For nitrogen, the differences were less than 0.2 dex, although there did appear to be a systematic difference of 0.1 dex between the two approaches. Dufton et al (2005) investigated this in detail and suggested that this arose from differences in the adopted nitrogen model atoms and wind effects.…”
Section: Methodsmentioning
confidence: 99%
“…The Si triplet (4552, 4567, and 4574 Å) was adopted as it is observed in effectively all our spectra and as they arise from the same multiplet, the effects of errors in the absolute oscillator strengths and non-LTE effects should be minimised. This method has been used previously by, for example, Dufton et al (2005), Hunter et al (2007), and Fraser et al (2010), who noted that it is sensitive to errors in the equivalent width measurements of the Si lines. Therefore the microturbulence was also estimated from requiring that the silicon abundance was consistent with that found in the LMC.…”
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...
“…Details of the methods adopted can be found in Hunter et al (2007), while a more detailed discussion of the grids can be found in Ryans et al (2003), Dufton et al (2005) 2 . Here only a brief summary will be given, with further details available as discussed above.…”
Section: Methodsmentioning
confidence: 99%
“…The validity of such an approach was investigated by Dufton et al (2005), who analysed the spectra of B-type Ia supergiants in the SMC using the current grid and also theoretical spectra generated by the code (Santolaya-Rey et al 1997;Puls et al 2005), that incorporates wind effects. Dufton et al (2005) found excellent agreement in the atmospheric parameters estimated from the two methods. Effective temperature estimates agreed to within typically 500 K, logarithmic gravities to 0.1 dex and microturbulent velocities to 2 km s −1 .…”
Section: Methodsmentioning
confidence: 99%
“…For nitrogen, the differences were less than 0.2 dex, although there did appear to be a systematic difference of 0.1 dex between the two approaches. Dufton et al (2005) investigated this in detail and suggested that this arose from differences in the adopted nitrogen model atoms and wind effects.…”
Section: Methodsmentioning
confidence: 99%
“…The Si triplet (4552, 4567, and 4574 Å) was adopted as it is observed in effectively all our spectra and as they arise from the same multiplet, the effects of errors in the absolute oscillator strengths and non-LTE effects should be minimised. This method has been used previously by, for example, Dufton et al (2005), Hunter et al (2007), and Fraser et al (2010), who noted that it is sensitive to errors in the equivalent width measurements of the Si lines. Therefore the microturbulence was also estimated from requiring that the silicon abundance was consistent with that found in the LMC.…”
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...
“…Assuming that all elements with an ionization potential lower than that of hydrogen and oxygen are fully ionized delivers an upper limit of q Metals < 9.5×10 −5 . For this, we used an SMC metallicity of 20% solar (see, e.g., Dufton et al 2005), and solar abundance values for the metals from Grevesse & Sauval (1998). This very low value obtained from the metals means that if hydrogen is ionized by only 1%, it still provides the dominant quantity of free electrons.…”
Context. B[e] supergiants are surrounded by large amounts of hydrogen neutral material, traced by the emission in the optical [Oi] lines. This neutral material is most plausibly located within their dense, cool circumstellar disks, which are formed from the (probably non-spherically symmetric) wind material released by the star. Neither the formation mechanism nor the resulting structure and internal kinematics of these disks (or disk-like outflows) are well known. However, rapid rotation, lifting the material from the equatorial surface region, seems to play a fundamental role. Aims. The B[e] supergiant LHA 115-S 65 (in short: S 65) in the Small Magellanic Cloud is one of the two most rapidly rotating B[e] stars known. Its almost edge-on orientation allows a detailed kinematical study of its optically thin forbidden emission lines. With a focus on the rather strong [Oi] lines, we intend to test the two plausible disk scenarios: the outflowing and the Keplerian rotating disk. Methods. Based on high-and low-resolution optical spectra, we investigate the density and temperature structure in those disk regions that are traced by the [Oi] emission to constrain the disk sizes and mass fluxes needed to explain the observed [Oi] line luminosities. In addition, we compute the emerging line profiles expected for either an outflowing disk or a Keplerian rotating disk, which can directly be compared to the observed profiles. Results. Both disk scenarios deliver reasonably good fits to the line luminosities and profiles of the [Oi] lines. Nevertheless, the Keplerian disk model seems to be the more realistic one, because it also agrees with the kinematics derived from the large number of additional lines in the spectrum. As additional support for the presence of a high-density, gaseous disk, the spectrum shows two very intense and clearly double-peaked [Caii] lines. We discuss a possible disk-formation mechanism, and similarities between S 65 and the group of Luminous Blue Variables.
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