An Introduction To Close Binary Stars Hilditch Pdf Download
Miina Hyrkas
Preface; 1. Close binary stars - a historical review; 2. Two-body orbital motion; 3. The determination of orbits; 4. Perturbations, the Roche model, and mass exchange/loss; 5. Photometry and polarimetry - stellar sizes and shapes; 6. Masses and absolute dimensions for stars in binaries; 7. The imaging of stellar surfaces and accretion structures; Problems; Outline answers; Bibliography.
Since the discovery of the first Double Periodic Variable stars by Mennickent et al. (2003), in the Large Magellanic Cloud (LMC) and the Small Magellanic Cloud (SMC), we have learnt that there is a new kind of semidetached, mass-transferring binary star showing two closely linked photometric variations. These systems show an enigmatic long period on average 33 times longer than the orbital period (Poleski et al. 2010; Pawlak et al. 2013; Mennickent et al. 2016b; Mennickent 2017). But an interesting and remarkable property of the Double Periodic Variables (DPVs) is the constancy of their orbital periods, which usually does not occur in the algols undergoing Roche Lobe Overflow mass transfer (Garrido et al. 2013). To date, it is suspected that some interacting binary systems show variations of the wind generated in the stream-disk impact region (van Rensbergen et al. 2008; Mennickent et al. 2016a), e.g., the interacting binary V393 Scorpii studied by Mennickent et al. (2012) shows evidence of a cyclically variable bipolar wind. The prototype β Lyrae is also a DPV and shows evidence of a jet emanating from the the accretion disk in a process far to be well understood (Harmanec et al. 1996).
Since we have independently distinguished the absorption lines of each component using the CORALIE spectra, we performed an iterative method of spectral disentangling proposed by González & Levato (2006), which is quite effective in separating the absorption lines of the stellar components. This method alternately uses the spectrum of one component to calculate the spectrum of the other one, hence eliminating gradually the spectral features of one stellar component until the convergence is assured and the flux contribution of its companion virtually disappears. In the process we used the theoretical radial velocities obtained from the sinusoidal fits in the previous section as input parameters until the seventh iteration for both components, obtaining successfully clean average spectra for both stars. The disentangling process for the gainer star reveals a double emission line in Hα, confirming the presence of circumstellar matter around the hot component. Furthermore, as the emission is double, an accretion disk is in principle inferred, in agreement with a semidetached algol mass-transferring binary (Figure 4).
The theoretical model considers a hot spot located on the edge of the disk, in the place where the gas stream from the donor falls encountering the disk. This active region is described by the ratio of the hot spot temperature and the unperturbed local disk temperature and the angular dimension and longitude of the spot. An additional bright spot with similar parameters is also included in the outer disk edge, following the results of hydrodynamical simulations of gas interchanged among close binary systems (e.g., Heemskerk 1994; Kaigorodov et al. 2017). The disk is assumed in physical contact with the gainer and is characterized by its radius Rd, outer, and inner edge thicknesses and its temperature:
According to our modern understanding, these systems are most likely formed from the moderately close binaries (Chen et al. 2016) through either nuclear evolution of the most massive component in the detached phase or angular momentum evolution of the two component stars within a convective envelope (Hilditch et al. 1988; Tutukov et al. 2004; Yildiz & Doğan 2013).
Abstract:In earlier papers, we presented a binary evolutionary code for the purpose of reproducing the orbital parameters, masses, radii, and location in the Hertzsprung Russell diagram (abbreviated as HRD) of well-observed Algol systems. In subsequent versions, the effects of mass and angular momentum losses and tidal coupling were included in order to produce the observed distributions of orbital periods and mass ratios of Algol-type binaries. The mass loss includes stellar wind and possible liberal evolution, when the gainer star is not capable to absorb all of the matter during mass transfer from the donor star. We added magnetic braking to our code to better reproduce the observed equatorial velocities. Large equatorial velocities of mass-gaining stars are now lowered by tidal interaction and magnetic braking. Tides are mainly at work at short orbital periods, leaving magnetic braking alone at work during longer orbital periods. The observed values of the equatorial velocities of mass gainers in Algol-type binaries are mostly well reproduced by our code. According to our models, Algols have short periods with a strong magnetic field.Keywords: eclipsing binaries; binary evolution; stellar mass loss; magnetic braking
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