  Multiple long and variable transits caused by dust from possibly
disintegrating asteroids were detected in light curves of WD 1145+017. We
present time-resolved spectroscopic observations of this target with QUCAM CCDs
mounted in the Intermediate dispersion Spectrograph and Imaging System at the
4.2-m William Herschel Telescope in two different spectral arms: the blue arm
covering 3800-4025 {\AA} and the red arm covering 7000-7430 {\AA}. When
comparing individual transits in both arms, our observations show with 20
{\sigma} significance an evident colour difference between the in- and
out-of-transit data of the order of 0.05-0.1 mag, where transits are deeper in
the red arm. We also show with > 6 {\sigma} significance that spectral lines in
the blue arm are shallower during transits than out-of-transit. For the
circumstellar lines it also appears that during transits the reduction in
absorption is larger on the red side of the spectral profiles. Our results
confirm previous findings showing the u'-band excess and a decrease in line
absorption during transits. Both can be explained by an opaque body blocking a
fraction of the gas disc causing the absorption, implying that the absorbing
gas is between the white dwarf and the transiting objects. Our results also
demonstrate the capability of EMCCDs to perform high-quality time resolved
spectroscopy of relatively faint targets.
