We present a three-dimensional (3D) study of common envelope events (CEEs) to provide a foundation for future one-dimensional (1D) methods to model the self-regulated phase of a CEE. The considered ...CEEs with a low-mass red giant end with one of three different outcomes – merger, slow spiral-in, or prompt formation of a binary. To understand which physical processes determine different outcomes, and to evaluate how well 1D simulations model the self-regulated phase of a CEE, we introduce tools that map our 3D models to 1D profiles. We discuss the differences in the angular momentum and energy redistribution in 1D and 3D codes. We identified four types of ejection processes: the pre-plunge-in ejection, the outflow during the plunge-in, the outflow driven by recombination, and the ejection triggered by a contraction of the circum-binary envelope. Significant mass is lost in all cases, including the mergers. Therefore, a self-regulated spiral-in can start only with a strongly reduced envelope mass. We derive the condition to start a recombination outflow, which can proceed either as a runaway or a stationary outflow. We show that the way the energy of the inspiralling companion is added to the envelope in 1D studies intensifies the envelope's entropy increase, alters the start of the recombination outflow, and leads to different outcomes in 1D and 3D studies. The steady recombination outflow may dispel most of the envelope in all slow spiral-in cases, making the existence of a long-term self-regulated phase debatable, at least for low-mass giant donors.
Common envelope events are important interactions between two binary stars that lead to the formation of close binary systems. We present here a systematic three-dimensional study in which we model ...common envelope events with low-mass giant donors. The results allow us to revise the energy formalism that is usually used to determine common envelope event outcomes. We show that the energy budget for this type of system should include the recombination energy, and that it also must take into account that a significant fraction of the released orbital energy is taken away by the ejecta. We provide three ways in which our results can be used by binary population synthesis studies: a relation that links the observed post-common envelope binary with the initial binary parameters, a fitting formula for the αceλ parameter of the standard energy formalism, and a revised energy formalism that takes into account both the recombination energy and the energy that is taken away by the ejecta.
In this Letter, we investigate the role of recombination energy during a common envelope event. We confirm that taking this energy into account helps to avoid the formation of the circumbinary ...envelope commonly found in previous studies. For the first time, we can model a complete common envelope event, with a clean compact double white dwarf binary system formed at the end. The resulting binary orbit is almost perfectly circular. In addition to considering recombination energy, we also show that between 1/4 and 1/2 of the released orbital energy is taken away by the ejected material. We apply this new method to the case of the double white dwarf system WD 1101+364, and we find that the progenitor system at the start of the common envelope event consisted of an ∼1.5 M⊙ red giant star in an ∼30 d orbit with a white dwarf companion.
V1309 Sco—UNDERSTANDING A MERGER NANDEZ, J L A; Ivanova, N; LOMBARDI, J C
Astrophysical journal/The Astrophysical journal,
05/2014, Letnik:
786, Številka:
1
Journal Article
Recenzirano
Odprti dostop
One of the two outcomes of a common envelope (CE) event is a merger of the two stars. To date, the best known case of a binary merger is the V1309 Sco outburst, where the orbital period was known and ...observed to decay up to the outburst. Using the hydrodynamical code StarSmasher, we study in detail which characteristics of the progenitor binary affect the outburst and produce the best match with observations. We have developed a set of tools in order to quantify any CE event. We consider binaries consisting of a 1.52 M sub(middot in circle) giant and a 0.16 M sub(middot in circle) companion with P sub(orb) ~ 1.4 days, varying the nature of the companion and its synchronization. We show that all considered progenitor binaries evolve toward the merger primarily because of Darwin instability. The merger is accompanied by mass ejection that proceeds in several separate mass outbursts and takes away a few percent of the donor mass. This very small mass, nonetheless, is important as it is not only sufficient to explain the observed light curve, but it also carries away up to one-third of both the initial total angular momentum and initial orbital energy. We find that all synchronized systems experience L sub(2) mass loss that operates during just a few days prior to the merger and produces ring-shaped ejecta. The formed star is always a strongly heated radiative star that differentially rotates. We conclude that the case of a synchronized binary with a main-sequence companion gives the best match with observations of V1309 Sco.
We synthesised a new type of photochromic tungsten oxide nanoparticles, analysed their photocatalytic activity and carried out a thorough analysis of their effect on prokaryotic and eukaryotic ...organisms. Ultrasmall hydrated tungsten oxide nanoparticles were prepared by means of hydrothermal treatment of tungstic acid in the presence of polyvinylpyrrolidone as a template, stabiliser and growth regulator. Tungstic acid was synthesised through an ion-exchange method using sodium tungstate solution and a strongly acidic cation exchange resin.
Upon illumination, photochromic nanoparticles of WO3 were shown to increase greatly their toxicity against both bacterial (both gram-positive and gram-negative – P. aeruginosa, E. coli and S. aureus) and mammalian cells (primary mouse embryonic fibroblasts); under the same conditions, fungi (C. albicans) were less sensitive to the action of tungsten oxide nanoparticles. UV irradiation of primary mouse fibroblasts in the presence of WO3 nanoparticles demonstrated a time- and dose-dependent toxic effect, the latter leading to a significant decrease in dehydrogenase activity and an increase in the number of dead cells. WO3 nanoparticles were photocatalytically active under both UV light and even diffused daylight filtered through a window glass, leading to indigo carmine organic dye discolouration.
The obtained experimental data not only show good prospects for biomedical applications of tungsten trioxide, but also demonstrate the need for clear control of biosafety when it is used in various household materials and appliances.
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•Photochromic WO3 nanoparticles were synthesised using ion-exchange method.•UV increased toxicity of WO3 nanoparticles against bacterial and mammalian cells.•WO3 nanoparticles were photocatalytically active under UV-illumination.
Cesium-promoted cobalt spinel is promising as a catalyst for the low-temperature decomposition of nitrous oxide for use in the second stage of a single-reactor unit for the combined removal of ...nitrogen oxides. This work studied the effect of the conditions for the preparation of granular and block bulk catalysts based on Co
3
O
4
by extrusion molding.
The production of nitric acid is one of the main industrial sources of nitrous oxide entering the atmosphere, which is an ozone-depleting gas with a potential 310 times higher than that of CO
2
. The ...review considers the catalytic systems and high- and low-temperature one-pot methods to reduce nitrous oxide emissions in the production of nitric acid. The existing catalysts provide 80–90% decomposition of nitrous oxide. For further increase in the degree of decomposition, it is required to develop more active and stable catalysts.
A scintillation experiment is a part of the TAIGA astrophysical complex located in the Tunka Valley, 50 km from Lake Baikal. It consists of the Tunka-Grande and TAIGA-Muon arrays. Its scientific ...program is devoted to the study of cosmic rays (CRs) and search for astrophysical gamma rays by detecting charged particles (electrons and muons) of extensive air showers (EASs). We present the current status of the scintillation experiment, methods of EAS and CR parameters’ reconstruction, the main results obtained by the Tunka-Grande array and our scientific program for the future.
•Efficient Cu-Ni catalysts supported on activated carbon for the water gas shift reaction.•Suppressed methanation activity due to the presence of Cu.•Cu–Ni alloy as a key factor of the catalytic ...design.•Good stability and tolerance towards start/stop situations.
The water-gas shift (WGS) reaction over structured Cu, Ni, and bimetallic Cu-Ni supported on active carbon (AC) catalysts was investigated. The structured catalysts were prepared in pellets form and applied in the medium range WGS reaction. A good activity in the 180–350°C temperature range was registered being the bimetallic Cu-Ni:2-1/AC catalyst the best catalyst. The presence of Cu mitigates the methanation activity of Ni favoring the shift process. In addition the active carbon gasification reaction was not observed for the Cu-containing catalyst converting the active carbon in a very convenient support for the WGS reaction. The stability of the bimetallic Cu-Ni:2-1/AC catalyst under continuous operation conditions, as well as its tolerance towards start/stop cycles was also evaluated.
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