The spectrum of BAL QSO Q1303+308: intrinsic variability and line-locking stability

A recently taken WHT optical spectrum of the BAL QSO Q1303+308 shows intere sting changes in the spectral characteristics of the absorption systems. In particular, the equivalent widths of many of the broad absorption lines ha ve markedly increased with respect to observations taken 15 yr earlier by F oltz et al., with the more blueshifted components showing the greatest incr ease by a factor of approximate to5 in optical depth. Perhaps the most rema rkable feature of the data is that, in the rest frame of the quasar, the li ne-of-sight outflow velocity of the clouds has only increased by approximat e to 55 km s(-1) in a rest-frame time interval of 5-6 yr. Various examples of doublet line locking are still visible in the system, and we present a p rovisional model analysis of the spectrum showing that theories based on sm all cloud velocity interactions via line locking can successfully explain t he general appearance of the spectrum and its variability. Finally we highl ight the need for further ongoing monitoring of this fascinating object.