Melampyrum Moravicum H. Braun. n. sp.

Braun, Heinrich

doi:10.1007/bf01643167

Cited by 43 publications

(63 citation statements)

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“…We computed the evolution of massive close binary systems using a computer code generated by Braun (1997) on the basis of an implicit hydrodynamic stellar evolution code for single stars (cf. Langer 1991Langer , 1998.…”

Section: Methodsmentioning

confidence: 99%

“…Thus, we derive the mass transfer rate implicitly using an iterative scheme (combined Secant/Bisection-method; cf. Press et al 1988), which is numerically more stable (Braun 1997). However, for each iteration a complete stellar model needs to be computed.…”

Section: Methodsmentioning

confidence: 99%

“…A time-dependent treatment of thermohaline mixing is important for identifying the borderline between contact and contact-free close binary systems as it occurs on the thermal time scale of the accreting star, which -at the borderline of contact-free systems -is just equal to the mass transfer time scale. I.e., a time dependent treatment is required to reproduce the radius evolution of the accreting star during the mass transfer phase correctly as soon as helium-enriched material is being transferred (cf., Braun 1997). …”

Section: Methodsmentioning

confidence: 99%

“…Numerically, we treat thermohaline mixing through a diffusion scheme (Braun 1997). The corresponding diffusion coefficient is based on the work of Stern (1960), Ulrich (1972), and Kippenhahn et al (1980); it reads…”

Section: Methodsmentioning

confidence: 99%

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Formation of contact in massive close binaries

Wellstein

Langer

Braun

2001

A&A

396

666

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Abstract. We present evolutionary calculations for 74 close binaries systems with initial primary masses in the range 12...25 M , and initial secondary masses between 6 and 24 M . The initial periods were chosen such that mass overflow starts during the core hydrogen burning phase of the primary (Case A), or shortly thereafter (Case B). We use a newly developed binary code with up-to-date physics input. Of particular relevance is the use of OPAL opacities, and the time-dependent treatment of semiconvective and thermohaline mixing. We assume conservative evolution for contact-free systems, i.e., no mass or angular momentum loss from those system except due to stellar winds. We investigate the borderline between contact-free evolution and contact, as a function of the initial system parameters. The fraction of the parameter space where binaries may evolve while avoiding contact -which we found already small for the least massive systems considered -becomes even smaller for larger initial primary masses. At the upper end of the considered mass range, no contact-free Case B systems exist. While for primary masses of 16 M and higher the Case A systems dominate the contact-free range, at primary masses of 12 M contact-free systems are more frequent for Case B. We identify the drop of the exponent x in the main sequence mass-luminosity relation of the form L ∝ M x as the main cause for this behaviour. For systems which evolve into contact, we find that this can occur for distinctively different reasons. While Case A systems are prone to contact due to reverse mass transfer during or after the primary's main sequence phase, all systems obtain contact for initial mass ratios below ∼ 0.65, with a merger as the likely outcome. We also investigate the effect of the treatment of convection, and found it relevant for contact and supernova order in Case A systems, particularly for the highest considered masses. For Case B systems we find contact for initial periods above ∼ 10 d. However, in that case (and for not too large periods) contact occurs only after the mass ratio has been reversed, due to the increased fraction of the donor's convective envelope. As most of the mass transfer occurs conservatively before contact is established, this delayed contact is estimated to yield to the ejection of only a fraction of the donor star's envelope. Our models yield the value of β, i.e., the fraction of the primaries envelope which is accreted by the secondary. We derive the observable properties of our systems after the major mass transfer event, where the mass gainer is a main sequence or supergiant O or early B type star, and the mass loser is a helium star. We point out that the assumption of conservative evolution for contact-free systems could be tested by finding helium star companions to O stars. Those are also predicted by non-conservative models, but with different periods and mass ratios. We describe strategies for increasing the probability to find helium star companions in observational search programs.

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Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

See 2 more Smart Citations

Formation of contact in massive close binaries

Wellstein

Langer

Braun

2001

A&A

396

666

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“…We are using a binary evolutionary code which was originally developed by Braun (1998) on the basis of an implicit hydrodynamic stellar evolution code for single stars (Langer 1991(Langer , 1998. It calculates simultaneous evolution of the two stellar components of a binary system in a circular orbit and the mass transfer within the Roche approximation (Kopal 1978).…”

Section: Numerical Code and Physical Assumptionsmentioning

confidence: 99%

Constraining the mass transfer in massive binaries through progenitor evolution models of Wolf-Rayet+O binaries

Petrović

Langer²,

Hucht

2005

A&A

180

250

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Abstract. Since close WR+O binaries are the result of a strong interaction of both stars in massive close binary systems, they can be used to constrain the highly uncertain mass and angular momentum budget during the major mass transfer phase. We explore the progenitor evolution of the three best suited WR+O binaries HD 90657, HD 186943 and HD 211853, which are characterized by a WR/O mass ratio of ∼0.5 and periods of 6...10 days. We are doing so at three different levels of approximation: predicting the massive binary evolution through simple mass loss and angular momentum loss estimates, through full binary evolution models with parametrized mass transfer efficiency, and through binary evolution models including rotation of both components and a physical model which allows to compute mass and angular momentum loss from the binary system as function of time during the mass transfer process. All three methods give consistently the same answers. Our results show that, if these systems formed through stable mass transfer, their initial periods were smaller than their current ones, which implies that mass transfer has started during the core hydrogen burning phase of the initially more massive star. Furthermore, the mass transfer in all three cases must have been highly non-conservative, with on average only ∼10% of the transferred mass being retained by the mass receiving star. This result gives support to our system mass and angular momentum loss model, which predicts that, in the considered systems, about 90% of the overflowing matter is expelled by the rapid rotation of the mass receiver close to the Ω-limit, which is reached through the accretion of the remaining 10%.

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The Analysis of Digitoxin Tablets

Banes

Carol

1953

Journal of the American Pharmaceutical Association (Scientific

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Melampyrum Moravicum H. Braun. n. sp.

Cited by 43 publications

References 0 publications

Formation of contact in massive close binaries

Formation of contact in massive close binaries

Constraining the mass transfer in massive binaries through progenitor evolution models of Wolf-Rayet+O binaries

The Analysis of Digitoxin Tablets

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