a) APT V (mV) magnitudes and (B − V) color of γ Cas over the 1998–2010 seasons of coverage; annual averages are shown. Error bars on these magnitudes (marked as * and X, respectively) are much smaller than the symbols, as each point represents a few hundred individual observations. Horizontal bars denote the coverage in time for each season’s average. Small points indicate each mV value measured in the 2010–2011 season. Annotations at the bottom give the column densities nHb in units of 1022 cm-2 responsible for the attenuations of soft X-rays in high dispersion X-ray observations of 2001, 2004, and 2010. b) the Hα emission equivalent widths (EW) in Ångstroms obtained by Pollmann and Bücke (star and square symbols, respectively over the same time as panel a)). A displacement of –1.0 Å was required to bring the the mean Bücke EW to the Pollmann mean. The vertical dotted lines correspond to times of the first and last XMM-Newton observations in 2010. Note the rapid Hα emission increase from 2002 on, and also a similar spike in 2007 as observed in 2010. Both events coincide with mV brightenings when panel a is plotted in high time resolution.
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