4.3.5 Stellar winds

Baschek, B.; Butler, K.; Scholz, M.; Ulmschneider, P.; Wehrsě, R.

doi:10.1007/10057805_15

Cited by 15 publications

(20 citation statements)

References 38 publications

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“…In the case of oxygen the O I triplet near λ7770 Å is fit using an abundance that is essentially solar, while O II lines from multiplets 64, 72 and 99 (Wiese et al multiplet numbering scheme) are well fit by a much lower abundance. These abundances, derived under the assumptions of LTE, are similar to those mentioned by Baschek et al (1977), who discuss the abundance in terms of non-LTE corrections.…”

Section: Synthetic Spectrum Analysissupporting

confidence: 74%

Emission lines in the optical spectrum of 3 Cen A

Wahlgren

Hubrig²

2004

A&A

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Abstract. Previously, weak emission lines had been detected at red wavelengths in the spectra of a limited sample of mid to late B type main sequence stars. A fuller description of the occurrence and origins of these lines has yet to be forwarded, in part due to the lack of observations detailing the spectral transitions involved. To address this deficiency, we present a line list of weak emission features found in the optical and near infrared spectral region of the chemically peculiar He-weak star 3 Cen A (HD 120709). Nearly 350 features, mostly associated with allowed transitions from high-excitation states of first ions, are catalogued along with identifications. Prominent among the emission lines are the spectra P II, Mn II, Fe II, Ni II and Cu II. Emission lines from Ca II, Si II and Hg II are also evident. Abundances are determined for several elements from synthetic spectrum fitting, with anomalies detected for the ions O I/II, P II/III and Si II/III. The LTE synthetic spectrum fitting also revealed that the low excitation 4s−4p transitions of Fe II predict an abundance that is greater than that determined from higher excitation 4d−4f transitions. Several of these latter transitions have upper energy levels that are found to be associated with emission lines. We also present empirical considerations for the excitation processes leading to the weak emission lines.

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Section: Synthetic Spectrum Analysissupporting

confidence: 74%

Emission lines in the optical spectrum of 3 Cen A

Wahlgren

Hubrig²

2004

A&A

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“…This same result was already found by Lambert et al 1982, whose measured equivalent widths agree with my own to within 2 to 3%. Lambert et al noted that this problem is caused by strong non-LTE effects in the multiplet (1) lines, as discussed by Baschek et al 1977. Since my analysis is restricted to LTE, I disregard the result from the multiplet (1) lines.…”

Section: Oxygen Z =mentioning

confidence: 97%

Abundances of the elements He to Ni in the atmosphere of Sirius A

Landstreet

2011

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Context. The abundances of elements in the atmosphere of an individual star provide a very broad range of extremely important information about the formation and evolution history of that star. Specifically, during the main sequence phase, the abundance pattern observed can provide valuable constraints on a range of hydrodynamical processes occurring beneath the visible atmosphere. Aims. Among middle main sequence (A and B) stars, it is unusual to have abundance determinations for more than about a dozen of the 30 lightest chemical elements, largely because many elements do not have usefully strong spectral lines in the visible wavelength window usually used for abundance analysis. Exceptionally, for the bright, sharp-lined hot Am star Sirius A = HD 48915, high resolution, high signal-to-noise ratio observations of the spectrum are available from 1265 Å to about 1 μm. The aim of this project is to determine generally how useful the UV part of the spectrum is for "generic" abundance determination in A stars, and which abundances of light and iron peak elements can be determined or improved for Sirius A using this nearly unique data set. Methods. The UV and visible spectrum of Sirius A has been searched for useful spectral lines of all elements up to nickel (2 ≤ Z ≤ 28), as well as the heavy elements Sr, Y, Zr and Ba. Using the spectrum synthesis code ZEEMAN, abundances or upper limits are derived. Results. Abundances relative to H have been determined for a total of 20 elements, and upper limits are found for 4 others. Useful measurements or limits are possible from these data for all but three of the elements through Ni. In particular, it is found that the light element B is underabundant relative to the Sun by a factor of at least 30. Conclusions. Recent computations have led to predictions of the abundance pattern of almost all the elements having Z ≤ 28 expected in the atmosphere of Sirius as a result of competition between (1) gravitationally and radiatively driven diffusion and either (2) turbulent mixing or (3) homogeneous mass loss. Comparison of these predictions with observations has been hampered by the limited number of elements for which accurate abundance determinations are available. The work presented here increases the number of elements for which reasonably well-determined abundances are available, and establishes more clearly the uncertainty of the abundance values for most of the elements up to Ni. The new data provide useful tests of the theoretical predictions of the consequences of atomic diffusion in slowly rotating A stars, and in some cases contradict them. These data may also provide some fresh insight into the evolution of the Sirius system. It appears that the new abundance values may be qualitatively consistent with the possibility that significant mass transfer has occurred between the two components of the system during its evolution.

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“…The maximum intensity of this pattern is reached for late A-type stars of the main sequence. The high sensitivity to the log g parameter does not alter the bell-shaped behaviour, which is enhanced at lower gravities even when the NLTE effect is included (Baschek et al 1977). In the second paper the NI 870.3 and 862.9 nm are analyzed in A-F supergiants.…”

Section: Cno Line Intensity Variation With T Effmentioning

confidence: 97%

C, N, O in $\mathsf{\lambda}$ Boo stars and in composite spectra

Faraggiana

Bonifacio

2005

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Abstract. The selective abundance of C, N, O (almost solar) with respect to that of other elements (underabundant) in λ Boo stars has been interpreted as a characteristic peculiarity of these objects, when considered as single stars. We show here that a similar selective abundance is predicted from the composite spectra resulting from two unresolved stars in the same temperature range as the λ Boo stars.

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4.3.5 Stellar winds

Cited by 15 publications

References 38 publications

Emission lines in the optical spectrum of 3 Cen A

Emission lines in the optical spectrum of 3 Cen A

Abundances of the elements He to Ni in the atmosphere of Sirius A

C, N, O in $\mathsf{\lambda}$ Boo stars and in composite spectra

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