Estudo Fotometrico e Espectroscopico de Asteroides Ricos em Volateis

Abstract

Seventeen asteroids of the main belt and three near earth asteroids have shown cometary activity. These objects have been called Active Asteroids (AA) (Jewitt, 2012). The physical source of their activity can be diverse; among the possible causes are collisional and volatile sublimation processes. The detection of AA is determined by the presence of a coma in the images, nevertheless this coma could be so faint that it would be very difficult to detect it, and therefore it would be desirable to have another method that indicates the possible presence of a coma in an asteroid. In this work we study the influence of a faint coma over the asteroid in the spectra. This has already been suggested by Carvano (2008) to the observe the atypical spectrum of the asteroid (5201) Ferraz-Mello and modeled by Carvano & Lorenz (2009) from which they were capable to produce a reflectance increase in shorter wavelengths, and shows that presence of a faint coma produces an unusual reflectance. In our model, we study more realistic distribution of particle in comae, to the consider different physical and chemical parameters that influence the formation of comae, where this coma is formed by sublimation or colisional ejection. This allowed us to analize the influence of this parameters in the spectra. The size distribution of particles in the coma, their optical properties, and the physical processes responsible for creating such distribution are complex and depend on many variables such that all this will influence in the obtained result. From our model it is evident that a coma in the asteroid modifies the observed spectra, but similar variations could be produced due to other processes, like phase angle effects or compositional inhomogeneitis on the asteroid surface. However, in most of the cases studied, the presence of a coma would produce an incrise in the reflectance in the bluer part of the spectrum which is uncommon on asteroid spectra and which could be used as indicator of a faint coma. This nevertheless would need to be confirmed by other means as brightness increases or extended radial profile analyses.