Context. This is the third of a series of papers on simulating the mechanisms acting currently on the Oort cloud and producing the observed long-period comets. Aims. In this paper we investigate the influence of current stellar perturbers on the Oort cloud of comets under the simultaneous galactic disk tide. We also analyse the past motion of the observed long-period comets under the same dynamical model to verify the widely used definition of dynamically new comets. Methods. The action of nearby stars and the galactic disk tide on the Oort cloud was simulated. The original orbital elements of all 386 longperiod comets of quality classes 1 and 2 were calculated, and their motion was followed numerically for one orbital revolution into the past, down to the previous perihelion. We also simulated the output of the close future pass of GJ 710 through the Oort cloud. Results. The simulated flux of the observable comets resulting from the current stellar and galactic perturbations, as well as the distribution of perihelion direction, was obtained. The same data are presented for the future passage of GJ 710. A detailed description is given of the past evolution of aphelion and perihelion distances of the observed long-period comets. Conclusions. We obtained no fingerprints of the stellar perturbations in the simulated flux and its directional structure. The mechanisms producing observable comets are highly dominated by galactic disk tide because all current stellar perturbers are too weak. Also the effect of the close passage of the star GJ 710 is very difficult to recognise on the background of the Galactic-driven observable comets. For the observed comets we found only 45 to be really dynamically "new" according to our definition based on the previous perihelion distance value.
The discovery of the first interstellar object (ISO) passing through the Solar System, 1I/2017 U1 ('Oumuamua), provoked intense and continuing interest from the scientific community and the general public. The faintness of 'Oumuamua, together with the limited time window within which observations were possible, constrained the information available on its dynamics and physical state. Some
The aim of this paper is to demonstrate the accuracy of our knowledge of close stellar passage distances in the pre-GAIA era. We used the most precise astrometric and kinematic data available at the moment and prepared a list of 40 stars nominally passing (in the past or future) closer than 2 pc from the Sun. We used a full gravitational potential of the Galaxy to calculate the motion of the Sun and a star from their current positions to the proximity epoch. For this calculations we used a numerical integration in rectangular, Galactocentric coordinates. We showed that in many cases the numerical integration of the star motion gives significantly different results than popular rectilinear approximation. We found several new stellar candidates for close visitors in past or in future.We used a covariance matrices of the astrometric data for each star to estimate the accuracy of the obtained proximity distance and epoch. To this aim we used a Monte Carlo method, replaced each star with 10 000 of its clones and studied the distribution of their individual close passages near the Sun. We showed that for contemporary close neighbours the precision is quite good but for more distant stars it strongly depends on the quality of astrometric and kinematic data. Several examples are discussed in detail, among them the case of HIP 14473. For this star we obtained the nominal proximity distance as small as 0.22 pc 3.78 Myr ago. However there exist strong need for more precise astrometry of this star since the proximity point uncertainty is unacceptably large.
The complete sample of large-perihelion nearly-parabolic comets discovered during the period 1901-2010 is studied starting from their orbit determination. Next, an orbital evolution that includes three perihelion passages (previous-observed-next) is investigated where a full model of Galactic perturbations and perturbations from passing stars have been incorporated.We show that the distribution of planetary perturbations suffered by actual largeperihelion comets during their passage through the Solar system has a deep, unexpected minimum around zero which indicates a lack of " almost unperturbed" comets. By a series of simulations we show that this deep well is moderately resistant to some diffusion of orbital elements of analysed comets. It seems reasonable to state that the observed stream of these large-perihelion comets experienced a series of specific planetary configurations when passing through the planetary zone.An analysis of the past dynamics of these comets clearly shows that dynamically new comets may appear only when their original semimajor axes are greater than 20 000 au. However, only for semimajor axes longer than 40 000 au dynamically old comets are completely not present. We demonstrated that the observed 1/a oridistribution exhibits a local minimum separating dynamically new from dynamically old comets.Long-term dynamical studies reveal a large variety of orbital behaviour. Several interesting examples of action of passing stars are also described, in particular the impact of Gliese 710 which will pass close to the Sun in the future. However, none of the obtained stellar perturbations is sufficient to change the dynamical status of analysed comets.
Context.First results based on Gaia data show that the well-known star Gliese 710 will be the closest flyby star in the next several Myrs and its minimum distance from the Sun will be almost five times smaller than that suggested by pre-Gaia solution.Aims. The aim of this work is to investigate the proximity parameters and the influence of the close approach of Gliese 710 on the basis of Gaia DR1. Furthermore, we compare new results with previous works based on HIP2 and Tycho 2 catalogues to demonstrate how Gaia improves the accuracy of determination of such phenomena. Methods. Using a numerical integration in an axisymmetric Galactic model, we determine new parameters of the close encounter for Gliese 710. Adding ten thousand clones drawn with the use of a covariance matrix, we estimate the most probable position and velocity of this star at the minimum distance from the Sun. Results. Our calculations show that Gliese 710 will pass 13 365 AU from the Sun in 1.35 Myr from now. At this proximity it will have the brightness of −2.7 mag and a total proper motion of 52.28 arcsec per year. After the passage of Gliese 710 we will observe a large flux of new long-period comets. Thanks to the Gaia mission, the uncertainties of the minimum distance and time of the close approach are several times smaller than suggested by previous works based on data from earlier observations.
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