Amplitude ΔB Research Articles

Frequent Flare Events on the Short-period M-type Eclipsing Binary BX Tri

We present long-term, multicolor photometric monitoring and spectroscopic observations of the short-period M-type eclipsing binary BX Tri. Six flare events were recorded over four years from 2014 to 2017. Three of them were detected on one night within an orbital cycle. The strongest one was identified on 2014 December 23. With the amplitudes ΔB = 0.48 mag, ΔV = 0.28 mag, ΔR = 0.10 mag, and ΔI = 0.02 mag, the total energy due to the flare event was measured to be 4.08 (±0.24) × 1034 erg, exceeding the superflare level (1034). Based on the observations, the evolutionary status of the binary system and the long-term orbital period changes were analyzed. It reveals that BX Tri is probably a semidetached system with the primary component filling its Roche lobe. The extremely high occurrence of flare events in the binary could be related to rapid mass transfer between the components.

Particle acceleration and Alfvén wave generation by an interplanetary shock

Based on the event observed by ISEE 3 near the Earth’s orbit at 01:21 UT on April 5, 1979, we investigate the diffusive shock acceleration of ions and the generation of Alfven waves by accelerated particles near the quasi-parallel parts of interplanetary shock fronts within a quasi-linear approach. The theory is shown to give an excessively high level of Alfven wave generation by accelerated particles at significant deflection angles of the interplanetary magnetic field from the normal to the shock front. At the Earth’s orbit, the Alfve´ n waves produced by accelerated ions are confined within the frequency range 5 × 10−2−0.5 Hz, and their spectral peak with a wave amplitude δB ≤ B corresponds to a frequency ν = (1−2)×10−2 Hz. The high-frequency part of the wave spectrum (ν ≥ 0.5 Hz) is subjected to damping on thermal protons. The calculated spectra of the accelerated ions and Alfven waves generated by them reproduce the main features observed in experiments.

Abell-35 Phenomena in Symbiotic Stars: Discovery of 1.2 and 6.4 Day Periods in VV8 (V471 Per)

Abstract We have collected high precision optical photometry of VV8, so far 782 individual observing runs uniformly distributed over the period 2005 - 2011. This dataset allows us to refine the known long periodicity of VV8 to P = 16.8 yr, with peak-to-valley amplitudes of ΔB = 0.18 and ΔV = 0.14 mag. In addition, we have discovered two new periodicities: 6.431 d (total amplitude ΔB = ΔV = ΔI = 0.05 mag) and 1.185 d (ΔB = 0.022, ΔV = 0.018, ΔI = 0.014 mag). These two short periods are reminiscent of the Abell-35 phenomena displayed by binary nuclei of planetary nebulae that have gone through a common envelope phase. Twice the 6.431 d period would nicely correspond to the double-peaked light-curve that the G5 III star in VV8 would display if its Roche lobe would be ellipsoidally distorted.

Accelerated ions and self-excited Alfvén waves at the Earth's bow shock

[1] The diffuse energetic ion event and related Alfvén waves upstream of the Earth's bow shock, measured by AMPTE/IRM satellite on 29 September 1984, 06:42–07:22 UT, was studied using a self-consistent quasi-linear theory of ion diffusive shock acceleration and associated Alfvén wave generation. The wave energy density satisfies a wave kinetic equation, and the ion distribution function satisfies the diffusive transport equation. These coupled equations are solved numerically, and calculated ion and wave spectra are compared with observations. It is shown that calculated steady state ion and Alfvén wave spectra are established during the time period of about 1000 s. Alfvén waves excited by accelerated ions are confined within the frequency range (10−2 to 1) Hz, and their spectral peak with the wave amplitude δB ≈ B comparable to the interplanetary magnetic field value B corresponds to the frequency 2 × 10−2 Hz. The high-frequency part of the wave spectrum undergoes absorption by thermal protons. It is shown that the observed ion spectra and the associated Alfvén wave spectra are consistent with the theoretical prediction.

The ongoing 2008���09 outburst of CI Cyg

In this paper, we discuss the early phases of the ongoing outburst that CI Cyg, a prototype symbiotic star, is currently undergoing after 30-year quiescence. We have tightly monitored CI Cyg in B V R c I c bands, starting a whole year before the onset of the outburst, and in addition we obtained numerous Echelle high- and low-resolution absolutely flux-calibrated spectra. The outburst started while the accreting white dwarf (WD) was being eclipsed by the Roche lobe filling M giant companion, and it was discovered during the egress phase on the second half of 2008 August. The system reached peak V-band brightness in early 2008 October and has been characterized by amplitudes ΔB = 1.9, ΔV = 1.5, ΔR C = 0.9, ΔI C = 0.4 mag. At maximum V-band brightness, the outbursting WD had expanded to closely resemble an F3 II/Ib star, with M v = -3.5, T eff ∼ 6900 K and R = 28 R ☉ . The high-ionization emission lines ([Ne v], [Fe VII], He II) disappeared and only lower ionization lines were visible. Balmer and He I emission lines declined in equivalent width but increased in absolute flux. The output radiated by the hot component during the outburst corresponds to nuclear burning proceeding at a 2 x 10 -8 M ☉ yr -1 rate.

Effects of nonlinear Alfvén wave interaction on particle diffusive shock acceleration. The Earth’s bow shock

We investigate the role of nonlinear Alfven-wave interaction in the diffusive shock acceleration of solar-wind ions at the Earth’s bow shock. Allowance for the nonlinear wave interaction through induced scattering and two-quanta absorption at plasma parameters β≲0.1 is shown to limit the Alfven-wave amplitude δB to δB≲B, whereas the quasi-linear approach predicts the generation of waves with amplitudes much larger than the diffusive shock magnetic field strength B. The nonlinear interaction results in spectral wave energy transfer to lower frequencies, which yields a significant increase in the particle acceleration rate.

Two‐dimensional simulations of magnetic pulsations upstream of the Earth's bow shock

The development of turbulence upstream of the quasi‐parallel portion of the Earth's bow shock is investigated using two‐dimensional hybrid simulations involving the injection of a very hot ion beam against a cold incident ion flow. Initially, waves are produced in the right‐hand resonant ion beam mode and with wave vectors mainly parallel to the ambient magnetic field B0 as expected in linear theory. The waves attempt to propagate upstream but are convected back toward the shock by the incident flow and strongly grow in amplitude as they encounter larger beam densities. Wave growth is associated with reduction of both incident and beam ion bulk velocities. Differential slowing of the incident flow between the different wave fronts and, when the angle θBn between B0 and the shock normal n is non zero, along the fronts themselves, leads to wave front refraction parallel to the shock and fragmentation into smaller structures. Simultaneously, strong scattering by the waves generates beam ion clumps containing a significant fraction of ions with velocities antiparallel to the beam bulk velocity, which enables the destabilization of the left‐hand resonant ion beam mode. The beam ions ultimately form a diffuse distribution whose density ratio relative to the solar wind is a few percents in average, but increases up to about 20% in the immediate vicinity of the shock. These processes result in the formation of magnetic pulsations whose extension parallel and perpendicular to n is typically 15 and a few tens of ion inertial lengths, respectively. These structures can reach total amplitudes δB of 3 to 4 B0, and exhibit most of the time a left‐handed polarization in the plasma rest frame, in agreement with spacecraft observations upstream of the Earth's bow shock. The simulations show that pulsations induce slowing and moderate heating of the incident flow and play an active role in the quasi‐parallel shock transition.

Model Images of Radio Halos Around Supernova Remnants

AbstractI present model calculations of profiles and two-dimensional images of the radio synchrotron emission of young supernova remnants, concentrating on observable effects of relativistic electrons diffusing upstream of the shock wave. If the preshock electron scattering mean free path is sufficiently long, observable synchrotron halos outside the bulk of the radio emission can potentially result; their absence can constrain the mean free path from above. If scattering is primarily due, as expected, to Alfvén waves with amplitude δB, the halo is expected to extend a distance of order rg c(δB/B)−2 /vs beyond the shock, where rg is the gyroradius of the electrons emitting at the observed frequency, B is the upstream magnetic field strength, vs is the shock velocity, and the amplitude δB refers to waves with wavelength comparable to rg , of order 1013 cm for typical supernova-remnant parameters. However, the detailed geometry of the halo varies with the assumptions about particle acceleration in the shock wave. I present an atlas of model profiles and images as a function of preshock diffusion length, of aspect angle between the magnetic field and the line of sight, and of other relevant parameters.Subject headings: radiation mechanisms: miscellaneous — shock waves — supernova remnants

Diffuse ions produced by electromagnetic ion beam instabilities

The evolution of the elecromagnetic ion beam instability driven by the reflected ion component backstreaming away from the earth's bow shock into the foreshock region is studied by means of computer simulation. The linear and quasi‐linear stages of the instability are found to be in good agreement with known results for the resonant mode propagating parallel to the beam along the magnetic field and with theory developed in this paper for the nonresonant mode, which propagates antiparallel to the beam direction. The quasi‐linear stage, which produces large amplitude δB ∼ B, sinusoidal transverse waves and “intermediate” ion distributions, is terminated by a nonlinear phase in which strongly nonlinear, compressive waves and “diffuse” ion distributions are produced. Additional processes by which the diffuse ions are accelerated to observed high energies are not addressed. The results are discussed in terms of the ion distributions and hydromagnetic waves observed in the foreshock of the earth's bow shock and of interplanetary shocks.

The X-Ray Sources Sco X-1 and Cyg X-2 as Binaries

The analysis of photometric observations of the X-ray source Sco X-1 leads to the conclusion of the existence of a periodic component in the light variations of this source. For 1966–74, the results can be presented as The photoelectric observations of some authors are shown in Figure 1, using the period. Figure 2 shows the mean light-curve of Sco X-1. The amplitude ΔB is about .