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The contact binary AW UMa has an extreme mass ratio, with the more massive component (the current primary) close to the main sequence, while the low mass star at q ~ 0.1 (the current secondary) has a much larger radius than a main sequence star of a comparable mass. We propose that the current secondary has almost exhausted hydrogen in its center and is much more advanced in its evolution, as suggested by Stepien. Presumably the current secondary lost most of its mass during its evolution with part of it transferred to the current primary. After losing a large fraction of its angular momentum, the binary may evolve into a system of FK Com type.
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High resolution spectroscopic observations of AW UMa, obtained on three consecutive nights with the median time resolution of 2.1 minutes, have been analyzed using the Broadening Functions method in the spectral window Doppler images of the system reveal the presence of vigorous mass motions within the binary system; their presence puts into question the solid-body rotation assumption of the contact binary model. AW UMa appears to be a very tight, semi-detached binary; the mass transfer takes place from the more massive to the less massive component. The primary, a fast-rotating star with V sin i = 181.4+-2.5 km s^-1, is covered by inhomogeneities: very slowly drifting spots and a dense network of ripples more closely participating in its rotation. The spectral lines of the primary show an additional broadening component (called the pedestal) which originates either in the equatorial regions which rotate faster than the rest of the star by about 50 km s^-1 or in an external disk-like structure. The secondary component appears to be smaller than predicted by the contact model. The radial velocity field around the secondary is dominated by accretion of matter transferred from (and possibly partly returned to) the primary component. The parameters of the binary are: A sin i = 2.73 +/- 0.11 R_odot and M_1 sin^3 i = 1.29 +/- 0.15 M_odot, M_2 sin^3 i = 0.128 +/- 0.016 M_odot. The mass ratio q_rm sp = M_2/M_1 = 0.099 +/- 0.003, while still the most uncertain among the spectroscopic elements, is substantially different from the previous numerous and mutually consistent photometric investigations which were based on the contact model. It should be studied why photometry and spectroscopy give so very discrepant results and whether AW UMa is an unusual object or that only very high-quality spectroscopy can reveal the true nature of W UMa-type binaries.
Based on results of Harding, Heunen, Lindenhovius and Navara, (2019), we give a connection between the category of AW*-algebras and their normal Jordan homomorphisms and a category COG of orthogemetries, which are structures that are somewhat similar to projective geometries, consisting of a set of points and a set of lines, where each line contains exactly 3 points. They are constructed from the commutative AW*-subalgebras of an AW*-algebra that have at most an 8-element Boolean algebra of projections. Morphisms between orthogemetries are partial functions between their sets of points as in projective geometry. The functor from the category of AW*-algebras with normal Jordan homomorphism to COG we create is injective on non-trivial objects, and full and faithful with respect to morphisms that do not involve type $I_2$ factors.
ER UMa stars are a recently recognized small subgroup of SU UMa-type dwarf novae, which are characterized by the extremely high outburst frequency and short (19--48 d) supercycles. From the current thermal-tidal disk instability scheme, they are considered to be high mass-transfer SU UMa-type dwarf novae, and comprise a link to permanent superhumpers below the period gap. They do not only provide an opportunity to test the applicability of thermal-tidal instability model but also pose problems on the origin of high mass-transfer in short orbital-period cataclysmic variables. A historical review of this subgroup and recent topics of ER UMa stars, the unique pattern of superhump evolution and the helium ER UMa analog (CR Boo), are also discussed.
It was recently demonstrated that contact binaries occur in globular clusters (GCs) only immediately below turn-off point and in the region of blue straggler stars (BSs). In addition, observations indicate that at least a significant fraction of BSs in these clusters was formed by the binary mass-transfer mechanism. The aim of our present investigation is to obtain and analyze a set of evolutionary models of cool, close detached binaries with a low metal abundance, which are characteristic of GC. We computed the evolution of 975 models of initially detached, cool close binaries with different initial parameters. The models include mass exchange between components as well as mass and angular momentum loss due to the magnetized winds for very low-metallicity binaries with Z = 0.001. The models are interpreted in the context of existing data on contact binary and blue straggler members of GCs. The model parameters agree well with the observed positions of the GC contact binaries in the Hertzsprung-Russell diagram. Contact binaries in the lower part of the cluster main sequence are absent because there are no binaries with initial orbital periods shorter than 1.5 d. Contact binaries end their evolution as mergers that appear in the BS region. Binary-formed BSs populate the whole observed BS region in a GC, but a gap is visible between low-mass mergers that are concentrated along the zero-age main sequence and binary BSs occupying the red part of the BS region. Very few binary mergers are expected to rotate rapidly and/or possess chemical peculiarities resulting from the exposure of the layers processed by CNO nuclear reactions. All other binary mergers are indistinguishable from the collisionally formed mergers. The results show that binary-formed BSs may constitute at least a substantial fraction of all BSs in a GC.
In this paper, we derive second order hydrodynamic traffic models from kinetic-controlled equations for driver-assist vehicles. At the vehicle level we take into account two main control strategies synthesising the action of adaptive cruise controls and cooperative adaptive cruise controls. The resulting macroscopic dynamics fulfil the anisotropy condition introduced in the celebrated Aw-Rascle-Zhang model. Unlike other models based on heuristic arguments, our approach unveils the main physical aspects behind frequently used hydrodynamic traffic models and justifies the structure of the resulting macroscopic equations incorporating driver-assist vehicles. Numerical insights show that the presence of driver-assist vehicles produces an aggregate homogenisation of the mean flow speed, which may also be steered towards a suitable desired speed in such a way that optimal flows and traffic stabilisation are reached.
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