Monitoring of Asteroids in Cometary Orbits and Active Asteroids

Abstract

Asteroids in Cometary Orbits (ACOs) are objects that behave dynamically like comets and have not shown any kind of activity in the past. Active Asteroids are objects that have typical asteroid orbits and have displayed gas and dust ejections. In this article, the results of the monitoring of 63 ACOs and four Active Asteroids are presented. ACOs were selected following a strict criterion based on their orbital parameters (Tancredi, 2014) so that they have a dynamical evolution similar to the periodic comets. Of the approximately 670000 asteroids discovered, a set of more than 600 objects classified as ACOs to this criterion was selected. The Active Asteroids were observed close to places in their orbit where activity had already been reported. Observations were made in 28 nights spread in different months during the years 2015, and 2016 at the Observatório Astronômico do Sertão de Itaparica (Itacuruba, Brazil) with the 1-m telescope of the IMPACTON project. The work consisted in the study of the surface brightness profile of the objects, in comparison with profiles of field stars, in search of a widening that would indicate the presence of cometary type activity. In addition, all the photometric data published in the Minor Planet Center database for the observed objects were extracted. The observed magnitudes were transformed to absolute magnitudes and compared with the available data, in order to search for possible unusual brightening. Surface brightness profiles were obtained for 42 of the 63 studied ACOs (approximately 6% of the initial sample) with no traces of activity in them, except for 2015 PD229 that is already cataloged as a comet (P/2015 PD229 ISON-Cameron), which showed a slight widening in its profile. Only one ACO exhibited significant variations of reduced magnitude: 174P/(60558) Echeclus, which is also already classified as asteroid and comet. A good profile for three Active Asteroids was obtained: 176P, 238P, and 288P. For the first two, there was no significant widening of the profile. Profiles with signs of activity were observed for 288P in three consecutive months (09-11/2016), close to the place in its orbit where activity had already been reported in 2011–2012. 238P was observed brighter than the mean reduced magnitude, two months before the first reports of activity, which would be an indicator that the activity was already present. It would be desirable to extend the list of observed ACOs and to continue monitoring the Active Asteroids to detect their potential reactivation. These observations are critical to address the different mechanisms to explain the activity of this set of objects.