Complicated Light Curves Research Articles

Dual-component plasma lens models

In contrast to the converging, achromatic behaviour of axisymmetric gravitational lenses, diverging frequency-dependent lensing occurs from refraction due to a distribution of over-dense axisymmetric plasma along an observer's line of sight. Such plasma lenses are particularly interesting from the point of view of astronomical observations because they can both magnify and dim the appearance of background sources as a function of frequency. Plasma lensing is believed to be involved in a number of separate phenomena involving the scintillation of radio pulsars, extreme scattering events of background radio sources and may also play a role in the generation of fast radio bursts. These lensing phenomena are believed to occur in dense environments, in which there may be many density perturbations between an observer and background source. In this work we generalize individual plasma lens models to produce dual component lenses using families of plasma lens models previously studied in the literature, namely the exponential and softened power-law lenses. Similar to binary gravitational lens models, these dual component plasma lenses feature a rich and complex critical and caustic morphology, as well as generate more complicated light curves. We map the number of criticals formed for a given component separation and angular size, and highlight a relevant degeneracy between two particular models. This work provides an argument in favor of close monitoring of extreme scattering events in progress in order to break such model degeneracies.

Accretion Disks around Black Holes: Dynamical Evolution, Meridional Circulations, and Gamma‐Ray Bursts

We study the hydrodynamic evolution of massive accretion disks around black holes, formed when a neutron star is disrupted by a black hole in a binary system. The initial conditions are taken from three-dimensional calculations of coalescing binaries. By assuming azimuthal symmetry we are able to follow the time dependence of the disk structure for 0.2 s in cylindrical coordinates (r, z). We use an ideal gas equation of state and assume that all the dissipated energy is radiated away. The disks evolve because of viscous stresses, modeled with an α law. We study the disk structure and, in particular, the strong meridional circulations that are established and persist throughout our calculations. These consist of strong outflows along the equatorial plane that reverse direction close to the surface of the disk and converge on the accretor. In the context of gamma-ray bursts (GRBs), we estimate the energy released from the system in neutrinos and through magnetic-dominated mechanisms and find it can be as high as Eν ≈ 1052 ergs and EBZ ≈ 1051 ergs, respectively, during an estimated accretion timescale of 0.1-0.2 s. The ν annihilation is likely to produce bursts from only a short, impulsive energy input L ∝ t-5/2 and so would be unable to account for a large fraction of bursts that show complicated light curves. On the other hand, a gas mass ≈0.1-0.25 M☉ survives in the orbiting debris, which enables strong magnetic fields ≈1016 G to be anchored in the dense matter long enough to power short duration GRBs. We highlight the effects that the initial disk and black holes masses, viscosity, and binary mass ratio have on the evolution of the disk structure. Finally, we investigate the continuous energy injection that arises as the black hole slowly swallows the rest of the disk and discuss its consequences on the GRB afterglow emission.

Precessing jets interacting with interstellar material as the origin for the light curves of gamma-ray bursts

We present an internal shock model with external characteristics for explaining the complicated light curves of gamma-ray bursts. Shocks produce gamma-rays in the interaction between a precessing beam of relativistic particles and the interstellar medium. Each time the particle beam passes the same line of sight with the observer the interstellar medium is pushed outward. Subsequent interactions between the medium and the beam are delayed by the extra distance to be travelled for the particles before the shock can form. This results in a natural retardation and leads to an intrinsic asymmetry in the light curves produced for gamma-ray bursts. In addition, we account for the cooling of the electron–proton plasma in the shocked region, which gives rise to an exponential decay in the gamma-ray flux. The combination of these effects and the precessing jet of ultrarelativistic particles produces light curves that can be directly compared with observed gamma-ray burst light curves. We illustrate the model by fitting a number of observed gamma-ray bursts that are difficult to explain with only a precessing jet. We develop a genetic algorithm to fit several observed gamma-ray bursts with remarkable accuracy. We find that for different bursts the observed fluence, assuming isotropic emission, easily varies over four orders of magnitude from the energy generated intrinsically.

Classification of the light curves of Mira variables

Based on an analysis of light curves of 223 long-period variables of the Mira Ceti type, recorded using the HIPPARCOS space telescope, it is shown that all the light curves of these stars can be divided by outward form into two groups: stars exhibiting simple light curves of sinusoidal shape and stars with complicated light curves, with hump-shaped formations on the ascending branch of the curve. Some observational parameters of the investigated stars display a tendency to separation into groups of stars with complicated and simple light curves. Stars with complicated light curves have longer periods, they are brighter in absolute bolometric magnitude, and there is a greater probability of detecting polarization in their light.

On the observed complexity of chaotic stellar pulsation

The existence of some variable stars producing very complicated light curves is well known. Theoretical calculations suggest that the irregular behaviour of the pulsation models in the RV Tauri and W Virginis regime is low dimensional is the result of period-doubling or tangent bifurcations (see e.g. Buchler and Kovacs 1987,Kovacs and Buchler 1988,Tanaka and Takeuti 1988).

On the Observed Complexity of Chaotic Stellar Pulsation

The existence of some variable stars producing very complicated light curves is well known. Theoretical calculations suggest that the irregular behaviour of the pulsation models in the RV Tauri and W Virginis regime is low dimensional is the result of period-doubling or tangent bifurcations (see e.g. Buchler and Kovács 1987, Kovács and Buchler 1988, Tanaka and Takeuti 1988).The light variation of the RV Tauri star R Scuti covering 150 years was analyzed by Kolláth (1990). A striking similarity was found between the reconstructed attractor of the Rössler model and that of the light variation of R Scuti. This result confirms the theoretical prediction of the existence of chaos, but a discrepancy still exists between the theory and observation. We could not find evidence for low dimension (D = 2– 3). The analyses of other stars also show rather erratic behaviour (e.g. Cannizzo and Goodings 1988, Cannizzo et al. 1990). A possible answer for this discrepancy is the treatment of stochastic perturbations by convection (Perdang 1991).

Flares of Orion population variables in the association Taurus T3

Thirteen new flare stars that are irregular variables of the Orion population have been found in an investigation of the Taurus Dark Cloud region by the homogeneous photographic multiexposure method using wide-angle Schmidt telescopes of the Byurakan Astrophysical Observatory. About 750 h of effective observation time led to the discovery of 17 flares in these stars. Analysis of the complicated light curves of the flares of these stars indicates a variety and multiplicity of phenomena and different dynamics of the energy release processes during the flares. The existence of flare stars that simultaneously exhibit the properties of T Tau and UV Cet type indicates that there is an intimate relationship between these types of young nonstationary stars. The flare star population in the region of the Taurus Dark Cloud is in all probability as young as the analogous groups of stars in Orion and Monoceros.

Photometeric study of the Beta Lyrae binary UU Cancri

Complicated light curves of the very long-period eclipsing binary UU Cnc (K4III, P=96.7 days) are made with the data obtained in UBV since 1984 at the Yonsei University Observatory. The overall shape of the light curves is Beta Lyr-type which resembles the one given by Eggen (1973) but with a slight deformation. The broad and shallow secondary eclipse seems to have a totality which lasts for about 10 days and is redder in B-V compared to that of the outside eclipse. The characteristics of each component of UU Cnc are discussed.

What tides and flares do to RS Canum Venaticorum binaries

view Abstract Citations (55) References (25) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS What tides and flares do to RS Canum Venaticorum binaries. Decampli, W. M. ; Baliunas, S. L. Abstract The effects that anisotropic mass should have on the orbital and spin states of RS Canum Venaticorum binaries are discussed. In the absence of magnetic fields, orbital period changes reported for several RS Canum Venaticorum systems require dM/dt of about 0.000001 solar masses/yr. Magnetic braking can lower this required rate if the surface magnetic fields are not less than 1000 gauss. However, this requires a method much more powerful than tidal torques to convert spin angular momentum loss to orbital angular momentum loss. This possibility is important when interpreting the complicated light curves of these systems, and may contradict the Hall's 'drifting star spot' hypothesis. In addition, large mass-loss rates may result in significant self-absorption of quiescent soft X-rays observed from several of these binaries. Publication: The Astrophysical Journal Pub Date: June 1979 DOI: 10.1086/157140 Bibcode: 1979ApJ...230..815D Keywords: Eclipsing Binary Stars; Flare Stars; Stellar Mass Ejection; Tides; Angular Momentum; Light Curve; Stellar Magnetic Fields; X Ray Absorption; Astrophysics; Mass Loss:RS CVn Stars; Period Changes:RS CVn Stars; RS CVn Stars:Stellar Flares full text sources ADS | data products SIMBAD (7)