Adiabatic Mass Loss and the Outcome of the Common Envelope Phase of Binary Evolution

We have developed a new method for calculating common envelope (CE) events based on explicit consideration of the donor star's structural response to adiabatic mass loss. In contrast to existing CE prescriptions, which specify a priori the donor's remnant mass, we determine this quantity self-consistently and find it depends on binary and CE parameters. This aspect of our model is particularly important to realistic modeling for upper main sequence star donors without strongly degenerate cores (and hence without a clear core/envelope boundary). We illustrate the central features of our method by considering CE events involving 10 solar mass donors on or before their red giant branch. For such donors, the remnant core mass can be as much as 30% larger than the star's He-core mass. Applied across a population of such binaries, our methodology results in a significantly broader remnant mass and final orbital separation distribution and a 20% increase in CE survival rates as compared to previous prescriptions for the CE phase.Comment: 4 pages, 3 figures; corrected typo in equation (1); updated reference dat

Towards Multiple-Star Population Synthesis

The multiplicities of stars, and some other properties, were collected recently by Eggleton & Tokovinin, for the set of 4559 stars with Hipparcos magnitude brighter than 6.0 (4558 excluding the Sun). In this paper I give a numerical recipe for constructing, by a Monte Carlo technique, a theoretical ensemble of multiple stars that resembles the observed sample. Only multiplicities up to 8 are allowed; the observed set contains only multiplicities up to 7. In addition, recipes are suggested for dealing with the selection effects and observational uncertainties that attend the determination of multiplicity. These recipes imply, for example, that to achieve the observed average multiplicity of 1.53, it would be necessary to suppose that the real population has an average multiplicity slightly over 2.0. This numerical model may be useful for (a) comparison with the results of star and star cluster formation theory, (b) population synthesis that does not ignore multiplicity above 2, and (c) initial conditions for dynamical cluster simulations

Evolution of the progenitor binary of V1309 Scorpii before merger

It was recently demonstrated that the eruption of V1309 Sco was a result of a merger of the components of a cool contact binary. We computed a set of evolutionary models of the detached binaries with different initial parameters to compare it with pre-burst observations of V1309 Sco. The models are based on our recently developed evolutionary model of the formation of cool contact binaries. The best agreement with observations was obtained for binaries with initial masses of 1.8-2.0 solar masses and initial periods of 2.5-3.1 d. The evolution of these binaries consists of three phases: at first the binary is detached and both components lose mass and angular momentum through a magnetized wind. This takes almost two thirds of the total evolutionary lifetime. The remaining third is spent in a semi-detached configuration of the Algol-type, following the Roche-lobe overflow by the initially more massive component. When the other component leaves the main sequence and moves toward the giant branch, a contact configuration is formed for a short time, followed by the coalescence of both components.Comment: 5 pages, 1 figure, Astronomy and Astrophysics, in prin

Acoustic confinement and Stimulated Brillouin Scattering in integrated optical waveguides

We examine the effect of acoustic mode confinement on Stimulated Brillouin Scattering in optical waveguides that consist of a guiding core embedded in a solid substrate. We find that SBS can arise due to coupling to acoustic modes in three different regimes. First, the acoustic modes may be guided by total internal reflection; in this case the SBS gain depends directly on the degree of confinement of the acoustic mode in the core, which is in turn determined by the acoustic V-parameter. Second, the acoustic modes may be leaky, but may nevertheless have a sufficiently long lifetime to have a large effect on the SBS gain; the lifetime of acoustic modes in this regime depends not only on the contrast in acoustic properties between the core and the cladding, but is also highly dependent on the waveguide dimensions. Finally SBS may occur due to coupling to free modes, which exist even in the absence of acoustic confinement; we find that the cumulative effect of coupling to these non-confined modes results in significant SBS gain. We show how the different acoustic properties of core and cladding lead to these different regimes, and discuss the feasibility of SBS experiments using different material systems

Low and intermediate-mass close binary evolution and the initial - final mass relation

Using Eggleton's stellar evolution code, we carry out 150 runs of Pop I binary evolution calculations, with the initial primary mass between 1 and 8 solar masses the initial mass ratio between 1.1 and 4, and the onset of Roche lobe overflow (RLOF) at an early, middle, or late Hertzsprung-gap stage. We assume that RLOF is conservative in the calculations, and find that the remnant mass of the primary may change by more than 40 per cent over the range of initial mass ratio or orbital period, for a given primary mass. This is contrary to the often-held belief that the remnant mass depends only on the progenitor mass if mass transfer begins in the Hertzsprung gap. We fit a formula, with an error less than 3.6 per cent, for the remnant (white dwarf) mass as a function of the initial mass of the primary, the initial mass ratio, and the radius of the primary at the onset of RLOF. We also find that a carbon-oxygen white dwarf with mass as low as 0.33 solar masses may be formed if the primary's initial mass is around 2.5 solar masses.Comment: 7 pages for main text, 11 pages for appendix (table A1), 12 figure

Optimizing optical Bragg scattering for single-photon frequency conversion

We develop a systematic theory for optimising single-photon frequency conversion using optical Bragg scattering. The efficiency and phase-matching conditions for the desired Bragg scattering conversion as well as spurious scattering and modulation instability are identified. We find that third-order dispersion can suppress unwanted processes, while dispersion above the fourth order limits the maximum conversion efficiency. We apply the optimisation conditions to frequency conversion in highly nonlinear fiber, silicon nitride waveguides and silicon nanowires. Efficient conversion is confirmed using full numerical simulations. These design rules will assist the development of efficient quantum frequency conversion between multicolour single photon sources for integration in complex quantum networks.Comment: 9 pages, 14 figure

Gap soliton formation by nonlinear supratransmission in Bragg media

A Bragg medium in the nonlinear Kerr regime, submitted to incident cw-radiation at a frequency in a band gap, switches from total reflection to transmission when the incident energy overcomes some threshold. We demonstrate that this is a result of nonlinear supratransmission, which allows to prove that i) the threshold incident amplitude is simply expressed in terms of the deviation from the Bragg resonance, ii) the process is not the result of a shift of the gap in the nonlinear dispersion relation, iii) the transmission does occur by means of gap soliton trains, as experimentally observed [D. Taverner et al., Opt Lett 23 (1998) 328], iv) the required energy tends to zero close to the band edge.Comment: 5 figures, submitted to EuroPhysics Letter

Pulse Evolution and Phase Sensitive Amplification in Silicon Waveguides

We for the first time provide an analytic solution for pulse propagation and phase sensitive amplification in the regime of high nonlinearity in silicon waveguides including two-photon absorption (TPA) and free carriers. Our analytic results clearly explain why and how the TPA and free carriers affect the signal gain. These observation are confirmed with numerical modelling and experimental results.Comment: We added the detailed derivation of the this pape

Modelling the formation of double white dwarfs

We investigate the formation of the ten double-lined double white dwarfs that have been observed so far. A detailed stellar evolution code is used to calculate grids of single-star and binary models and we use these to reconstruct possible evolutionary scenarios. We apply various criteria to select the acceptable solutions from these scenarios. We confirm the conclusion of Nelemans et al. (2000) that formation via conservative mass transfer and a common envelope with spiral-in based on energy balance or via two such spiralins cannot explain the formation of all observed systems. We investigate three different prescriptions of envelope ejection due to dynamical mass loss with angular-momentum balance and show that they can explain the observed masses and orbital periods well. Next, we demand that the age difference of our model is comparable to the observed cooling-age difference and show that this puts a strong constraint on the model solutions. However, the scenario in which the primary loses its envelope in an isotropic wind and the secondary transfers its envelope, which is then re-emitted isotropically, can explain the observed age differences as well. One of these solutions explains the DB-nature of the oldest white dwarf in PG1115+116 along the evolutionary scenario proposed by Maxted et al. (2002a), in which the helium core of the primary becomes exposed due to envelope ejection, evolves into a giant phase and loses its hydrogen-rich outer layers.Comment: 20 pages, 17 figures, 6 tables, accepted for publication in Astronomy and Astrophysics. See http://www.astro.uu.nl/~sluys/publications/ for high-resolution versions of Figs. 15 and 1