V606 Cen: A Newly Formed Massive Contact Binary in a Hierarchical Triple System

V606 Centauri (V606 Cen) is an early B-type close binary with an orbital period of 1.4950935 days, and its complete light curves are very difficult to observe on the ground. By analyzing the continuous light curve obtained by TESS, we found that it is a marginal contact binary with a very low fill-out factor of about 2%. The O − C diagram of V606 Cen is constructed for the first time based on 118.8 yr of eclipse times. The O − C diagram has been found to show a downward parabolic change together with a cyclic oscillation with a semiamplitude of 0.0545 days and a period of 88.3 yr. The downward parabolic variation reveals a linear period decrease at a rate of dP/dt = −2.08 × 10−7 days yr−1 that can be explained by the mass transfer from the more massive component to the less massive one. Both the marginal contact configuration and the continuous period decrease suggest that V606 Cen is a newly formed contact binary via Case A mass transfer. The cyclic change in the O − C diagram can be explained by the light-travel time effect via the presence of a third body. The lowest mass of the tertiary companion is determined to be M 3 = 4.51 (±0.43) M ⊙ and the tertiary is orbiting around the central eclipsing binary in a nearly circular orbit (e = 0.33). All of the results indicate that V606 Cen is a newly formed massive contact binary in a hierarchical triple system.

Electron spectra for twisted electron collisions

Ionization collisions have important consequences in many physical phenomena, and the mechanism that leads to ionization is not universal. Double differential cross sections (DDCSs) are often used to identify ionization mechanisms because they exhibit features that distinguish close collisions from grazing collisions. In the angular DDCS, a sharp peak indicates ionization through a close binary collision, while a broad angular distribution points to a grazing collision. In the DDCS energy spectrum, electrons ejected through a binary encounter collision result in peak at an energy predicted from momentum conservation. These insights into ionization processes are well-established for plane wave projectiles. However, the recent development of sculpted particle wave packets reopens the question of how ionization occurs for these new particle wave forms. We present theoretical DDCSs for (e,2e) ionization of atomic hydrogen for electron vortex projectiles. Our results predict that the ionization mechanism for vortex projectiles is similar to that of non-vortex projectiles, but that the projectile’s momentum uncertainty causes noticeable changes to the shape and magnitude of the vortex DDCSs. Specifically, there is a broadening and splitting of the angular DDCS peak for vortex projectiles, and an increase in the cross section for high energy ejected electrons.

THE 3-D NUMERICAL SIMULATIONS OF THE SMALL RADIUS ACCRETION DISK FORMATION IN MICROQUASAR CYG X-1. THE CASE OF THE HIGH RESOLUTION GRID IN THE VERTICAL DIRECTION

The present paper is devoted to small radius accretion disk formation in microquasar CYG X-1. The results show that in the case of the strong wind action on a disk the disk radius is about of 20 ÷ 30 per sent of accretor’s Roche lobe radius (it is about of 0.08 of orbital separation) instead of the standard disk radius equal to 80 ÷ 85 per sent of accretor’s Roche lobe radius (the last magnitude is a disk radius equal to 0.22 of orbital separation). In the present paper we try to resolve the problem that is arising in the case of microquasars when we investigate the accretion disk formation in these objects. Indeed, since the microquasars are the massive close binary systems (MCBS) in which the donor is massive stars of O-B class the strong wind is blowing from these stars. In this case the problem is arising: what is the situation in which an accretion disk in microqausars is formed. By the other words, it means what are the processes and the matter that are responsible for an accretion disk formation in microquasars: is this matter from one-point stream only or a disk is formed from the donor’s wind in essential or one is formed from both processes simul- taneously. This question is not idle since one is strong affects on ON-OFF state generations in the precession mechanism model. Since this mechanism is strong depending from the magnitude of the disk centre density and all the parameters affecting on it are very important for calculations. The matter configuration in the vicinity of one-point is one of these parameters that strong affects on ON-OFF state production and disk structure and the central disk density. By this reason we have investigated in the present paper how the disk structure is depending from the wind configuration in the vicinity of one-point.

THE 3-D NUMERICAL SIMULATIONS OF THE DEPENDENCE OF THE DISK STRUCTURE FROM THE WIND CONFIGURATION IN ONE-POINT IN MICROQUASAR CYG X-1. THE CASE OF THE HIGH RESOLUTION GRID IN THE VERTICAL DIRECTION

The present paper is devoted to the investigation how the disk structure is depending from the one-point wind one in microquasar CYG X-1. The results show that when the region in which the wind is absent in the vicinity of one-point has the size less or equal to 0.07 the disk radius is very small, order of 0.08 in units of orbital separation. When this size is increased to 0.115 the disk radius becomes to be of standard size to be equal to 0.22 in units of orbital separation. By the other words these results show that the disk structure is strong depending from many factors including and the donor’s wind configuration in the vicinity of one-point. This configuration is inherent to microquasars only. Indeed, since microqausars are the massive close binary systems; the donor in these systems is massive star from which the strong radiation- driving wind is blowing. On the other hand, in microquasars accretion disks are present and it means that one-point stream is also present in microqausars. It in turn means that the matter configuration in the vicinity of one-point is very complicated since the high mass loss rate donor’s wind and one-point stream must be existing in the vicinity of one-point simultaneously. This situation maybe resolved when we suppose that the central source in an accretion disk will influence on the donor’s atmosphere structure in the vicinity of one-point and in turn will be result in the break of wind in the vicinity of one-point. This finally will be means that one-point stream will be existing in one-point without a wind and it, flowing in the accretor’s Roche lobe, will be result in an accretion disk forma- tion. Here one problem is arising: what is the configuration of wind in the extended vicinity of one-point and from what the parameters this configuration is depending and haw this configuration will be results to the disk structure change. We good understand that this situation is arising in the case of microquasars only and we try to resolve this problem in the present paper.

Stellar Chromospheric Variability

Cool stars with convective envelopes of spectral types F and later tend to exhibit magnetic activity throughout their atmospheres. The presence of strong and variable magnetic fields is evidenced by photospheric starspots, chromospheric plages and coronal flares, as well as by strong Ca ii H+K and Hα emission, combined with the presence of ultraviolet resonance lines. We review the drivers of stellar chromospheric activity and the resulting physical parameters implied by the observational diagnostics. At a basic level, we explore the importance of stellar dynamos and their activity cycles for a range of stellar types across the Hertzsprung–Russell diagram. We focus, in particular, on recent developments pertaining to stellar rotation properties, including the putative Vaughan–Preston gap. We also pay specific attention to magnetic variability associated with close binary systems, including RS Canum Venaticorum, BY Draconis, W Ursae Majoris and Algol binaries. At the present time, large-scale photometric and spectroscopic surveys are becoming generally available, thus leading to a resurgence of research into chromospheric activity. This opens up promising prospects to gain a much improved understanding of chromospheric physics and its wide-ranging impact.

Close Binary Stars in Planetary Nebulae through Gaia EDR3

The aim of this work is to search for evidence of close binary stars associated with planetary nebulae (ionized stellar envelopes in expansion) by mining the astronomical archive of Gaia EDR3. For this task, using big data techniques, we selected a sample of central stars of planetary nebulae from almost 2000 million sources in an EDR3 database. Then, we analysed some of their parameters, which could provide clues about the presence of close binary systems, and we ran a statistical test to verify the results. Using this method, we concluded that red stars tend to show more affinity with close binarity than blue ones.

Effect of tides on the orbital evolution of the redback system PSR 1723-2837

The standard model of stellar evolution in Close Binary Systems assumes that during mass transfer episodes the system is in a synchronised and circularised state. Remarkably, the redback system PSR J1723-2837 has an orbital period derivative $\dot{P}_{orb}$ too large to be explained by this model. Motivated by this fact, we investigate the action of tidal forces in between two consecutive mass transfer episodes for a system under irradiation feedback, which is a plausible progenitor for PSR J1723-2837. We base our analysis on Hut’s treatment of equilibrium tidal evolution, generalised by considering the donor as a two layers object that may not rotate as a rigid body. We also analyse three different relations for the viscosity with the tidal forcing frequency. We found that the large value measured for $\dot{P}_{orb}$ can be reached by systems where the donor star rotates slower (by few per cent) than the orbit just after mass transfer episodes. Van Staden & Antoniadis have observed this object and reported a lack of synchronism, opposite to that required by the Hut’s theory to account for the observed $\dot{P}_{orb}$. Motivated by this discrepancy, we analyse photometric data obtained by the spacecraft Kepler second mission K2, with the purpose of identifying the periods present in PSR J1723-2837. We notice several periods close to those of the orbit and the rotation. The obtained periods pattern reveals the presence of a more complex phenomenology, which would not be well described in the frame of the weak friction model of equilibrium tides.

Neutrino pair annihilation ($$\nu {\bar{\nu }}\rightarrow e^-e^+$$) in the presence of quintessence surrounding a black hole

Quintessence fields, introduced to explain the speed-up of the Universe, might affect the geometry of spacetime surrounding black holes, as compared to the standard Schwarzschild and Kerr geometries. In this framework, we study the neutrino pairs annihilation into electron-positron pairs ($$\nu {\bar{\nu }}\rightarrow e^-e^+$$ ν ν ¯ → e - e + ) near the surface of a neutron star, focusing, in particular, on the Schwarzschild-like geometry in presence of quintessence fields. The effect of the latter is to increase the photon-sphere radius ($$R_{ph}$$ R ph ), increasing in such a way the maximum energy deposition rate near to $$R_{ph}$$ R ph . The rate turns out to be several orders of magnitude greater than the rate computed in the framework of General Relativity. These results might provide a rising in the GRBs energy emitted from a close binary neutron star system and might be used to constraints the parameters of the quintessence model. Finally we theoretically study the effects of rotation on the neutrino energy deposition.