No abstract

Photometric observations of the nearly equal-mass binary near-Earth asteroid 2017 YE5 were carried out at the Observatório Astronômico do Sertão de Itaparica (OASI, Brazil) and at the Blue Mountains Observatory (BMO, Australia) between July and August 2018, shortly after it made a close approach to Earth in June 2018. These observations allowed to determine an orbital period of the system in good agreement with the result of the radar observations. Our results also indicate that the 2017 YE5 system is not fully locked in a synchronous spin-orbit resonance, as there is a possible asynchronous component or tumbling rotator in the system. Additional data obtained at the Observatorio Astronómico Nacional de San Pedro Mártir (OAN-SPM, Mexico) in August 2018 allowed to derive the colour indices and the low resolution spectrum, which indicate that the object has a very reddish surface similar to the outer Solar system objetcs. This is consistent with a dark albedo of about 3 per cent, derived from an effective diameter of the combined components and an absolute magnitude of 19.2. Infrared data obtained at the NASA’s IRTF exhibit a thermal emission in the 2.5 μm range for which a low albedo of 2-4 per cent was adjusted by applying a thermal model. Regarding to the taxonomic classification, we found that the 2017 YE5 is a D-type in the Bus-DeMeo taxonomy. Therefore, according to our results and considering that the 2017 YE5 system has a typical comet orbit (TJ = 2.87), we suggest that it is a dormant Jupiter-family binary comet.

Fenômenos como eclipses despertam o interesse e a curiosidade dos seres humanos desde a Antiguidade. Em virtude disso, a monitoração sistematizada desses eventos poderia ser utilizada para despertar o interesse das pessoas desde uma simples contemplação, ou pelo interesse didático ou para pesquisa científica. O objetivo do presente trabalho é estimular a aplicação e desenvolvimento de pesquisas científicas no ambiente escolar. Para isso, propõe-se a monitoração de eclipses solares. Registros fotográficos serão obtidos pelos estudantes, utilizando equipamento apropriado para a observação solar. Em análises das fotos, serão determinados parâmetros representativos das características e da evolução desses interessantes eventos astronômicos. Os resultados poderão ser comparados com previsões de alta precisão. Uma descrição pormenorizada da metodologia e dos recursos a serem empregados nas observações é também fornecida.

No abstract

The goal of the present paper is to develop a simplified model to describe the gravitational fields of elongated asteroids. The proposed model consists of representing an elongated asteroid using a triple-particle-linkage system distributed in the three-dimensional space and it is an extension of previous planar models. A non-linear optimisation method is used to determine the parameters of our model, minimising the errors of all the external equilibrium points with respect to the solutions calculated with a more realistic approach, the Mascon model, which are assumed to give the real values of the system. The model considered in this article is then applied to three real irregular asteroids: 1620 Geographos, 433 Eros, and 243 Ida. The results show that the current triple-particle-linkage three-dimensional model gives better accuracy when compared to the axisymmetric triple-particle-linkage model available in the literature, and provides an advantage in terms of accuracy over the mass point model, while keeping computational time low. This model is also used to carry out simulations to characterise regions with solutions that remain bounded or that escape from around each asteroid under analysis. We investigated initial inclinations of 0○ (direct orbits) and 180○ (retrograde orbits). We considered the gravitational field of the asteroid, the gravitational attraction of the Sun, and the SRP. Our results are then compared to the results obtained using the Mascon gravitational model, based on the polyhedral shape source. We found good agreement between the two models.