Orbital stability of S-type circumbinary planets

Nowadays, more than 4,000 exoplanets have been discovered, including a hundred of circumbinary planets. In the following work, the orbital variations of 67 S-type circumbinary planets have been studied. Their orbital evolutions for a thousand years are simulated using the REBOUND package. The published physical and orbital parameters of the systems are used to computed the systems’ orbital instability limits: Roche limit and Hill’s sphere. From 67 systems, there are two unstable circumbinary systems: Kepler-420 and GJ 86. Kepler-420 Ab orbit passes into the system’s Roche limit due to its high orbital eccentricity. For GJ 86 Ab, the planet orbits outside its Hill’s sphere. The instability of GJ 86 Ab might be caused by an inaccurate measurement of GJ 86 A physical parameters. Using the GJ 86 A mass obtained from Farihi et al., the planet orbits in the stable orbit zone.

A bound on chaos from stability

We explore the quantum chaos of the coadjoint orbit action of diffeomorphism group of S1. We study quantum fluctuation around a saddle point to evaluate the soft mode contribution to the out-of-time-ordered correlator. We show that the stability condition of the semi-classical analysis of the coadjoint orbit found in [1] leads to the upper bound on the Lyapunov exponent which is identical to the bound on chaos proven in [2]. The bound is saturated by the coadjoint orbit Diff(S1)/SL(2) while the other stable orbit Diff(S1)/U(1) where the SL(2, ℝ) is broken to U(1) has non-maximal Lyapunov exponent.

Strangeness of translational and rotational motion of the geosynchronous object 10294 according to optical observations

Представлены особенности изменения параметров движения геосинхронного объекта 10294 SIRIO-1 №1977-080A по результатам оптических наблюдений в обсерваториях в Звенигороде, на пике Терскол и на горе Санглох республики Таджикистан. Пассивный итальянский научный космический аппарат SIRIO-1 представляет интерес тем, что он описывает классическую восьмерку вокруг точки либрации 75 ◦ в.д. без дрейфа по долготе и всегда доступен наблюдениям с наших пунктов. Это дает возможность детально исследовать поступательно-вращательное движение объекта, используя только результаты своих измерений. SIRIO-1 наблюдался нами для проверки аппаратуры и программного обеспечения как тестовый объект с очень устойчивой орбитой. В 2018 г. у этого объекта были обнаружены изменения в движении и в кривых блеска, не свойственные космическому мусору. Были зафиксированы небольшое скачкообразное изменение орбиты между 7 и 11 марта 2018 г. и изменение коэффициента отношения площади миделевого сечения объекта к его массе; кроме того перестал надежно определяться период изменения блеска и появилось характерное изменение блеска на одном и том же участке траектории с периодом, примерно равным звездным суткам. The features of changes in the motion parameters of the geosynchronous object 10294 SIRIO-1 No.1977-080A based on the results of optical observations at the observatories in Zvenigorod, Terskol Peak and Sanglokh Mountain in the Republic of Tajikistan are presented. The passive Italian scientific spacecraft SIRIO-1 is of interest to us because it describes the classic eight around the libration point of 75 ◦ E without longitude drift and is always available to observations from our observation points. This makes it possible to study in detail the translational-rotational motion of the object, using only the results of their measurements. SIRIO-1 was observed by us to test the hardware and software as a test object with a very stable orbit. In 2018, this object was found to have changes in motion and in the light curves that are not characteristic to space debris. A small abrupt change in the orbit between March 7 and 11, 2018, and a change in the area-to-mass ratio of the object were recorded. In addition, the period of change in the brightness was no longer reliably determined, and a characteristic change in the brightness appeared on the same part of the trajectory with a period approximately equal to the sidereal day.

Particle orbiting motion in a confined microvortex

Particle motion in viscous fluids is a common and fascinating phenomenon. The hydrodynamics of a trapped finite-size particle recirculating along a stable orbit within a microvortex is still puzzling. Herein we report experimental observations of the orbiting motion of a finite-size particle in a vortex confined in a microcavity. The orbiting particle keeps crossing the streamlines with acute changes in velocity along the orbit, which can be divided into three stages: acceleration, swerving, and following. By examining the relationship between particle orbit and vortex streamlines, we uncover a particle slingshot effect and slip motion. Particle motion and vortex structure in three dimensions are also studied, revealing many new fascinating particle motion phenomena. The results provide new insights into the physics of particle motion in vortices.

Living on the edge: Rossby wave instability and HFQPOs in black hole binaries

Context. The Rossby wave instability (RWI) has been proposed to explain the origin of the high-frequency quasi-periodic oscillations observed in the X-ray emission of astrophysical systems harbouring black holes. Recent numerical computations have proven that the RWI does exist in a general relativistic context and that its presence is associated with a time-variable X-ray emission from the disc. Aims. Using our new Numerical Observatory of Violent Accreting system, NOVAs, we explore the way the RWI impacts an accretion disc orbiting a spinning black hole under realistic astrophysical conditions. Our aim is to study the impact of the presence of the RWI in the very inner part of the accretion disc on known observables and explore some possibly new ones. Methods. We present the first full general relativistic hydrodynamical simulations of the RWI occurring at the last stable orbit of an accretion disc orbiting around a Kerr black-hole. Those simulations, coupled with a full general relativistic ray-tracing, have allowed us to directly compare our simulations with the observables we obtained from the X-ray emission of the disc. Results. Our study shows, for the first time, that the RWI naturally arises near the inner edge of an accretion disc whenever it gets close to its last stable orbit, as predicted analytically. From there, we show that not only does the RWI create a visible timing feature but it also impacts the energy spectrum of the source, which exhibits a high energy extension due to the presence of hot vortices generated by the RWI in the disc. Our study also shows that systems with the RWI present at the inner edge of the disc only exhibit similar behavior to systems in which HFQPOs have been detected.

Orbit Determination of 2002 KM6

The premise of this research is to determine the orbit of the asteroid 99795 2002 KM6 and predict its trajectory far in the future. Asteroids’ orbits model ellipses and can thus be described by six orbital elements: the semi-major axis, eccentricity, inclination, the longitude of the ascending node, the argument of perihelion, and the mean anomaly. Using Python, our team programmed a series of orbital determination codes, implementing the Method of Gauss to generate the orbital elements with a reasonable level of error. This required gathering data over at least three observations. We then compared these elements to those generated by JPL Horizons to ensure they were reasonable.Our team used the numerical integration program Swift to determine long-term orbital patterns over the next 50 million years. Simulations of 60 different clones of 2002 KM6, randomly sampled from a Gaussian distribution, revealed that the majority of asteroid particles will either get too far or too close to the Sun after 50 million years. A small percentage of them, however, will maintain a stable orbit.

Analysis of the possibility of creating a stable satellite about the asteroid Apophis as a homogeneous triaxial ellipsoid

The task of creating a stable orbit of the Apophis asteroid satellite as a homogeneous triaxial ellipsoid is investigated. The simulation of the motion of the spacecraft around the asteroid was performed taking into account the main perturbations: from the attraction of celestial bodies, asteroids non-sphericity and solar radiation pressure, and taking into account the asteroids own rotation. It is shown that it is possible to create a stable orbit of an asteroid satellite. This orbit can be used for a detailed study of the characteristics of the asteroid and the refinement of its orbit using ground radio measurements of the motion of a satellite equipped with a radio beacon.

Nuclear γ-ray emission from very hot accretion flows

Optically thin accretion plasmas can reach ion temperatures Ti ≥ 1010 K and thus trigger nuclear reactions. Using a large nuclear interactions network, we studied the radial evolution of the chemical composition of the accretion flow toward the black hole and computed the emissivity in nuclear γ-ray lines. In the advection dominated accretion flow (ADAF) regime, CNO and heavier nuclei are destroyed before reaching the last stable orbit. The overall luminosity in the de-excitation lines for a solar composition of plasma can be as high as few times 10−5 the accretion luminosity (Ṁc2) and can be increased for heavier compositions up to 10−3. The efficiency of transformation of the kinetic energy of the outflow into high energy (≥100 MeV) γ-rays through the production and decay of π0-mesons can be higher, up to 10−2 of the accretion luminosity. We show that in the ADAF model up to 15% of the mass of accretion matter can “evaporate” in the form of neutrons.