Dynamical tides in exoplanetary systems containing hot Jupiters: Confronting theory and observations

We study the effect of dynamical tides associated with the excitation of gravity waves in an interior radiative region of the central star on orbital evolution in observed systems containing hot Jupiters. We consider WASP-43, OGLE-TR-113, WASP-12 and WASP-18 that contain stars on the main sequence (MS). For these systems there are observational estimates regarding the rate of change of the orbital period.We also investigate Kepler-91 that contains an evolved giant star.We adopt the formalism of Ivanov et al. for calculating the orbital evolution. For the MS stars we determine expected rates of orbital evolution under different assumptions about the amount of dissipation acting on the tides, estimate the effect of stellar rotation for the two most rapidly rotating stars and compare results with observations. All cases apart from possibly WASP-43 are consistent with a regime in which gravity waves are damped during their propagation over the star. However, at present this is not definitive as observational errors are large. We find that although it is expected to apply to Kepler-91, linear radiative damping cannot explain this dissipation regime applying to MS stars. Thus, a non-linear mechanism may be needed. Kepler-91 is found to be such that the time-scale for evolution of the star is comparable to that for the orbit. This implies that significant orbital circularization may have occurred through tides acting on the star. Quasi-static tides, stellar winds, hydrodynamic drag and tides acting on the planet have likely played a minor role.We are grateful to G. I. Ogilvie for his important remarks and suggestions. SVC and PBI were supported in part by RFBR grants 15-02-08476 and 16-02-01043, by programme 7 of the Presidium of Russian Academy of Sciences and also by Grant of the President of the Russian Federation for Support of the Leading Scientific Schools NSh-6595.2016.2

On the formation of a quasi-stationary twisted disc after a tidal disruption event

We investigate misaligned accretion discs formed after tidal disruption events that occur when a star encounters a supermassive black hole. We employ the linear theory of warped accretion discs to find the shape of a disc for which the stream arising from the disrupted star provides a source of angular momentum that is misaligned with that of the black hole. For quasi-steady configurations we find that when the warp diffusion or propagation time is large compared to the local mass accretion time and/or the natural disc alignment radius is small, misalignment is favoured. These results have been verified using SPH simulations. We also simulated 1D model discs including gas and radiation pressure. As accretion rates initially exceed the Eddington limit the disc is initially advection dominated. Assuming the $\alpha$ model for the disc, where it can be thermally unstable it subsequently undergoes cyclic transitions between high and low states. During these transitions the aspect ratio varies from $\sim 1$ to $\sim 10^{-3}$ which is reflected in changes in the degree of disc misalignment at the stream impact location. For maximal black hole rotation and sufficiently large values of viscosity parameter $\alpha > \sim 0.01-0.1$ the ratio of the disc inclination to that of the initial stellar orbit is estimated to be $0.1-0.2$ in the advection dominated state, while reaching of order unity in the low state. Misalignment descreases with decrease of $\alpha$, but increases as the black hole rotation parameter decreases. Thus, it is always significant when the latter is small.MXG acknowledges support through Leopoldina fellowship programme (fellowship number LPDS 2009-50). Simulations were performed using the Darwin Supercomputer of the University of Cambridge High Performance Computing Service, provided by Dell Inc. using Strategic Research Infrastructure Funding from the Higher Education Funding Council for England and funding from the Science and Technology Facilities Council. MXG also acknowledges the computing time granted (NIC project number 8163) on the supercomputer JUROPA at Jülich Supercomputing Centre (JSC). PBI was supported in part by RFBR grants 15-02-08476 and 16-02-01043 and also by Grant of the President of the Russian Federation for Support of the Leading Scientific Schools NSh-6595.2016.2.This is the final version of the article. It first appeared from Oxford University Pressvia https://doi.org/10.1093/mnras/stw213

The evolution of a supermassive retrograde binary embedded in an accretion disk

In this note we discuss the main results of a study of a massive binary with unequal mass ratio, q, embedded in an accretion disk, with its orbital rotation being opposed to that of the disk. When the mass ratio is sufficiently large, a gap opens in the disk, but the mechanism of gap formation is very different from the prograde case. Inward migration occurs on a timescale of t_ev ~ M_p/(dot M), where M_p is the mass of the less massive component (the perturber), and dot M is the accretion rate. When q<< 1, the accretion takes place mostly onto the more massive component, with the accretion rate onto the perturber being smaller than, or of order of, q^(1/3)M. However, this rate increases when supermassive binary black holes are considered and gravitational wave emission is important. We estimate a typical duration of time for which the accretion onto the perturber and gravitational waves could be detected

The Secular Evolution of a Uniform Density Star Cluster Immersed in a Compressible Galactic Tidal Field

Abstract Nuclear stellar clusters are common in the center of galaxies. We consider the possibility that their progenitors assumed to be globular clusters may have formed elsewhere, migrated to, and assembled near their present location. The main challenge for this scenario is whether globular clusters can withstand the tidal field of their host galaxies. Our analysis suggests that provided the mass-density distribution of background potential is relatively shallow, as in some galaxies with relatively flat surface brightness profiles, the tidal field near the center of galaxies may be shown to be able to compress rather than disrupt a globular cluster at a distance from the center much smaller than the conventionally defined “tidal disruption radius” r t . To do so, we adopt a previously constructed formalism and consider the secular evolution of star clusters with a homogeneous mass-density distribution. We analytically solve the secular equations in the limit that the mass density of stars in the galactic center approaches a uniform distribution. Our model indicates that a star cluster could travel to distances much smaller than r t without disruption, thus potentially contributing to the formation of the nuclear cluster. However, appropriate numerical N-body simulations are needed to confirm our analytic findings.</jats:p

High-harmonic generation: taking control of polarization

The ability to control the polarization of short-wavelength radiation generated by high-harmonic generation is useful not only for applications but also for testing conservation laws in physics

Degradation of structure and properties of rail surface layer at long-term operation

The microstructure evolution and properties variation of the surface layer of rail steel after passed 500 and 1000 million tons of gross weight (MTGW) have been investigated. The wear rate increases to 3 and 3.4 times after passed 500 and 1000 MTGW, respectively. The corresponding friction coefficient decreases by 1.4 and 1.1 times. The cementite plates were destroyed and formed the cementite particles of around 10-50 nm in size after passed 500 MTGW. The early stage dynamical recrystallization was observed after passed 1000 MTGW. The mechanisms for these have been suggested. The large number of bend extinction contours is revealed in the surface layer. The internal stress field is evaluated

To respond or not to respond - a personal perspective of intestinal tolerance

For many years, the intestine was one of the poor relations of the immunology world, being a realm inhabited mostly by specialists and those interested in unusual phenomena. However, this has changed dramatically in recent years with the realization of how important the microbiota is in shaping immune function throughout the body, and almost every major immunology institution now includes the intestine as an area of interest. One of the most important aspects of the intestinal immune system is how it discriminates carefully between harmless and harmful antigens, in particular, its ability to generate active tolerance to materials such as commensal bacteria and food proteins. This phenomenon has been recognized for more than 100 years, and it is essential for preventing inflammatory disease in the intestine, but its basis remains enigmatic. Here, I discuss the progress that has been made in understanding oral tolerance during my 40 years in the field and highlight the topics that will be the focus of future research

Baryogenesis through split Higgsogenesis

We study the cosmological evolution of asymmetries in the two-Higgs doublet extension of the Standard Model, prior to the electroweak phase transition. If Higgs flavour-exchanging interactions are sufficiently slow, then a relative asymmetry among the Higgs doublets corresponds to an effectively conserved quantum number. Since the magnitude of the Higgs couplings depends on the choice of basis in the :Higgs doublet space, we attempt to formulate basis-independent out-of-equilibrium conditions. We show that an initial asymmetry between the fliggs scalars, which could be generated by GP violation in the :Higgs sector, will be transformed into a baryon asymmetry by the sphalerons, without the need of B ¿ L violation. This novel mechanism of baryogenesis through (split) Higgsogenesis is exemplified with simple scenarios based on the out-of-equilibrium decay of heavy singlet scalar fields into the illiggs doublets

Histone H3 Localizes to the Centromeric DNA in Budding Yeast

During cell division, segregation of sister chromatids to daughter cells is achieved by the poleward pulling force of microtubules, which attach to the chromatids by means of a multiprotein complex, the kinetochore. Kinetochores assemble at the centromeric DNA organized by specialized centromeric nucleosomes. In contrast to other eukaryotes, which typically have large repetitive centromeric regions, budding yeast CEN DNA is defined by a 125 bp sequence and assembles a single centromeric nucleosome. In budding yeast, as well as in other eukaryotes, the Cse4 histone variant (known in vertebrates as CENP-A) is believed to substitute for histone H3 at the centromeric nucleosome. However, the exact composition of the CEN nucleosome remains a subject of debate. We report the use of a novel ChIP approach to reveal the composition of the centromeric nucleosome and its localization on CEN DNA in budding yeast. Surprisingly, we observed a strong interaction of H3, as well as Cse4, H4, H2A, and H2B, but not histone chaperone Scm3 (HJURP in human) with the centromeric DNA. H3 localizes to centromeric DNA at all stages of the cell cycle. Using a sequential ChIP approach, we could demonstrate the co-occupancy of H3 and Cse4 at the CEN DNA. Our results favor a H3-Cse4 heterotypic octamer at the budding yeast centromere. Whether or not our model is correct, any future model will have to account for the stable association of histone H3 with the centromeric DNA

Theory of disk accretion onto supermassive black holes

Accretion onto supermassive black holes produces both the dramatic phenomena associated with active galactic nuclei and the underwhelming displays seen in the Galactic Center and most other nearby galaxies. I review selected aspects of the current theoretical understanding of black hole accretion, emphasizing the role of magnetohydrodynamic turbulence and gravitational instabilities in driving the actual accretion and the importance of the efficacy of cooling in determining the structure and observational appearance of the accretion flow. Ongoing investigations into the dynamics of the plunging region, the origin of variability in the accretion process, and the evolution of warped, twisted, or eccentric disks are summarized.Comment: Mostly introductory review, to appear in "Supermassive black holes in the distant Universe", ed. A.J. Barger, Kluwer Academic Publishers, in pres