To explain the phenomenon of metal pollution of White Dwarfs (WD) photospheres, we compared three main fragmentation mechanisms of small bodies (SB): tidal force, thermal destruction, and sublimation when SB fall onto WD along star-grazing orbits. The temperatures of the WDs lie in the range of 3,000 K to 15,000 K. We consider two materials, using their internal strength: crystalline ice and chondrite. We show that inside the Roche limit, ice bodies (ISB) ranging in size from 60 meters to 150 kilometres are destroyed by tidal forces. The corresponding sizes of stony bodies (SSB) range from 90 meters to 130 kilometres. Bodies of centimetre size are subject to sublimation. The thermal destruction mechanism is effective for bodies whose size lies in the interval where tidal forces and sublimation are not so effective, destroying SSBs smaller than 50 meters and ISBs smaller than 1 kilometre near stars with T_eff ≤ 15 000 K. Such bodies are totally destroyed by thermal tensile stresses long before they reach the Roche limit. There may be observable manifestations of SB falling in the form of short-term flashes of the order of a second from SSB with sizes ≤ 100 meters and WD curtaining with dust tails from ISB, causing WD dimming for a short time of the order of an hour. We conjecture that SB, moving along elongated elliptical orbits at large distances from the star, disintegrates by thermal destruction. The fragments from debris disks have nothing to do with the Roche limit.

International Scientific Optical Network (ISON) is an open international voluntary project specializing in observations of the near-Earth space objects. Observatories collaborating with ISON provide the global coverage and successfully combine the observations of the space debris and asteroids. The network includes more than 50 telescopes of 27 observatories in 15 countries and has been working since 2005. ISON monitors the whole GEO region and tracks the objects at GEO, GTO, HEO and LEO. ISON data allowing maintenance of the database of the space objects orbits, validating space debris population model and providing conjunction assessment analysis for satellites at high orbits. ISON develops the technology of asteroid survey with small telescopes and arranges regular photometry observations of near-Earth asteroids (NEA) to investigate the YORP effect, search new binary NEAs, and support radar experiments.

We consider a mechanism for the deposition of dust grains on to the surface of cold white dwarfs (WDs). Calculations show that grains can fall on to a cold WD directly, without reaching the phase of complete evaporation, if the parent bodies and the grains orbit on elongated, close to parabolic, orbits. To this end, we calculated the dynamics of evaporating silicate and graphite dust grains moving in circular and parabolic orbits around the white dwarf WD J1644−0449 with T_eff ≈ 3830 K and M_⋆ = 0.45 M_⊙. The calculations accounted for the influence of radiation pressure and Poynting–Robertson drag on the grain dynamics. The results show that silicate grains of all sizes considered that leave the parent bodies on circular orbits evaporate completely at a distance of ∼3 stellar radii (R_⋆) from the star. The boundary of the dust-free zone for graphite grains is closer to the star, ∼1.5R_⋆, and is represented confidently only for larger grains with radius > 0.5 |${\mu m}$|⁠. We determined the lower limits of the radius for grains capable of reaching the stellar surface. For comparison, we analysed the dependences of lower size limits for infalling silicate grains for a set of WDs within the temperature range 3000–5000 K. We conclude that silicate grains with an initial size ≥ 300 |${\mu m}$| can reach the surface of WD J1644−0449. For stars with temperatures in the range 3000–5000 K, the corresponding grain size range is 0.016 μm–5 cm.

We present the conceptual framework of the Astronomical Hub (AstroHub), a unified platform combining various optical instruments at a single observatory. Its major approach lies in arranging conditions for research groups to install telescopes and equipment and participate in joint projects. AstroHub is planned to integrate Virtual Observatory (VO) tools, FAIR data principles, and a telescope network to create a powerful and attractive ecosystem for both robust near-Earth object (NEO) monitoring and diverse deep space research. We provide an overview of the AstroHub development directions in the case study of the Assy-Turgen Observatory.