Unveiling Vela - Time Variability of Interstellar Lines in the Direction
  of the Vela Supernova Remnant II. Na D and Ca II
  In a survey conducted between 2011-12 of interstellar Na I D line profiles in
the direction of the Vela supernova remnant, a few lines of sight showed
dramatic changes in low velocity absorption components with respect to profiles
from 1993-1994 reported by Cha & Sembach. Three stars - HD 63578, HD 68217 and
HD 76161 showed large decrease in strength over the 1993-2012 interval. HD
68217 and HD 76161 are associated with the Vela SNR whereas HD 63578 is
associated with $\gamma^2$ Velorum wind bubble. Here, we present high spectral
resolution observations of Ca II K lines obtained with the Southern African
Large Telescope (SALT) towards these three stars along with simultaneous
observations of Na I D lines. These new spectra confirm that the Na D
interstellar absorption weakened drastically between 1993-1994 and 2011-2012
but show for the first time that the Ca II K line is unchanged between
1993-1994 and 2015. This remarkable contrast between the behaviour of Na D and
Ca II K line absorption lines is a puzzle concerning gas presumably affected by
the outflow from the SNR and the wind from $\gamma^2$ Velorum.
