2017MNRAS.465.3267G

WD 1145+017 was observed from 2015 November to 2016 July, for the purpose of characterizing transit behaviour of the white dwarf by dust clouds thought to be produced by fragments of an asteroid in close orbit with the star. Fortuitously, most of these observations were carried out during a time when the overall 'dip' activity was dramatically enhanced over that during its discovery with Kepler K2. By the end of our reported observations, the dip activity had declined to a level close to its K2 discovery state. Three notable events were observed. In 2016 January, a large number of dust clouds appeared that had an orbital period of 4.4912 h, and this event also marked the end of a three-month interval dominated by the K2 'A' period. The second event was a 2016 April 21 appearance of four dip features with drift lines in a waterfall (date versus phase) diagram that diverged from their origin date, at a location away from the 'A' asteroid, and which lasted for two weeks. The third event was the sudden appearance of a dip feature with a period of 4.6064 h, which is essentially the same as the K2 'B' period. The evolution of dip shape, depth, and total fade amount provide constraints on dust production and loss mechanisms. Collisions can account for the sudden appearance of dust clouds, and the sudden increase in dust amount, but another mechanism for continual dust production is also required.