Periodic Reporting for period 3 - Cat-In-hAT (Catastrophic Interactions of Binary Stars and the Associated Transients)
Reporting period: 2022-01-01 to 2023-06-30
One of the crucial formation channels of compact object binaries composed of white dwarfs, neutron stars, and black holes, including sources of gravitational waves, critically depends on catastrophic binary interactions accompanied by the loss of mass, angular momentum, and energy (“common envelope” evolution - CEE). Despite its importance, CEE is perhaps the least understood major phase of binary star evolution and progress in this area is urgently needed to interpret observations from the new facilities (gravitational wave detectors, time-domain surveys). Recently, the dynamical phase of the CEE has been associated with a class of transient brightenings exhibiting slow expansion velocities and copious formation of dust and molecules - red transients. A number of features of red transients, especially the long timescale of mass loss, challenge the existing CEE paradigm.
Motivated by these transients, the project Cat-In-hAT aims to develop a new variant of magnetohydrodynamics to comprehensively examine the 3D evolution of CEE from the moment when the mass loss commences to the remnant phase. The objectives are to resolve the long timescales observed in the red transients, characterize binary stability in 3D with detailed microphysics, to illuminate the fundamental problem of how is orbital energy used to unbind the common envelope in a regime that was inaccessible before, and to break new ground on the amplification of magnetic fields during CEE. This project will establish red transients as an entirely new probe of the CEE physics by comparing detailed theoretical predictions of light curves from different viewing angles, spectra, line profiles, and polarimetric signatures with observations. The project will accomplish this by coupling multi-dimensional moving mesh hydrodynamics with radiation, dust formation, and chemical reactions. Finally, the project will examine the physical processes in the aftermath of red transients on timescales of years to centuries after the outburst, connect with the proposed merger products, and to identify them in time-domain surveys.
Motivated by these transients, the project Cat-In-hAT aims to develop a new variant of magnetohydrodynamics to comprehensively examine the 3D evolution of CEE from the moment when the mass loss commences to the remnant phase. The objectives are to resolve the long timescales observed in the red transients, characterize binary stability in 3D with detailed microphysics, to illuminate the fundamental problem of how is orbital energy used to unbind the common envelope in a regime that was inaccessible before, and to break new ground on the amplification of magnetic fields during CEE. This project will establish red transients as an entirely new probe of the CEE physics by comparing detailed theoretical predictions of light curves from different viewing angles, spectra, line profiles, and polarimetric signatures with observations. The project will accomplish this by coupling multi-dimensional moving mesh hydrodynamics with radiation, dust formation, and chemical reactions. Finally, the project will examine the physical processes in the aftermath of red transients on timescales of years to centuries after the outburst, connect with the proposed merger products, and to identify them in time-domain surveys.
In the first half of the project we have focused predominantly on the radiation hydrodynamics of Common Envelope Evolution preceding and immediately following the dynamical inspiral. So far, we have exhaustively characterized outflows from binary stars initiated with a range of initial positions and velocities. We found that outflows can achieve positive energy and leave to infinity if launched from specific positions and with a range of velocities, which are more complicated than previously thought. We also
argued that Sh 2-71 is the best known example of planetary nebula formed by Common Envelope ejection in a triple star system. We showed with high-quality space-based data that light curves of at least some classical novae are powered by shock interaction. Classical novae are in many aspects similar to common envelope events, and the connection between these two types of events is only starting to be fully explored. We performed hydrodynamical simulations of spherical explosion colliding with aspherical matter distribution with the aim of identifying which observable quantities can be used to discriminate between various environments. This is important, because different matter distributions point to different physical processes responsible for their creation. We comprehensively analyzed the progenitor and explosion of luminous red nova AT2018bwo with the help of observations, binary evolution models, and models for transient light curves. We also successfully combined multi-dimensional moving-mesh hydrodynamics and radiation transport. Our first application was for wind-reprocessed transients, but this is the tool we will use extensively to understand common envelope ejections.
argued that Sh 2-71 is the best known example of planetary nebula formed by Common Envelope ejection in a triple star system. We showed with high-quality space-based data that light curves of at least some classical novae are powered by shock interaction. Classical novae are in many aspects similar to common envelope events, and the connection between these two types of events is only starting to be fully explored. We performed hydrodynamical simulations of spherical explosion colliding with aspherical matter distribution with the aim of identifying which observable quantities can be used to discriminate between various environments. This is important, because different matter distributions point to different physical processes responsible for their creation. We comprehensively analyzed the progenitor and explosion of luminous red nova AT2018bwo with the help of observations, binary evolution models, and models for transient light curves. We also successfully combined multi-dimensional moving-mesh hydrodynamics and radiation transport. Our first application was for wind-reprocessed transients, but this is the tool we will use extensively to understand common envelope ejections.
There are two already achieved results beyond the state of the art. First, multi-dimensional radiation hydrodynamics on radially-moving mesh (Calderon et al. 2021) is a unique tool that allows to study various systems over many orders of magnitude in space and time. This achievement is a key point to reach the goals of the project related to common envelope transients, which we plan to address in the rest of the project. Second, in Blagorodnova et al. (2021) we for the first time combined archival observations of progenitor, detailed binary evolution modeling, and interpretation of the transients brightening and present a coherent picture of binary star merger.
We expect that until the end of the project we will apply our newly-developed moving-mesh radiation hydrodynamics tool to common-envelope transients to determine the mechanism that powers them. We also expect to perform (magneto)hydrodynamical simulation in the low-Mach regime relevant for certain stages of common envelope.
We expect that until the end of the project we will apply our newly-developed moving-mesh radiation hydrodynamics tool to common-envelope transients to determine the mechanism that powers them. We also expect to perform (magneto)hydrodynamical simulation in the low-Mach regime relevant for certain stages of common envelope.