tokens: may be higher given that an unmeasurable component of light is lost during this period. No conclusion can or should be drawn from this point, which is presented only for the sake of completeness. 3.2 He <sc>i</sc> line 3.2.1 Equivalent width The equivalent widths of the He i line around the 2014 periastron are shown in Fig. 4 (b). The closed blue circles denote the equivalent width as measured by integrating from the base of the line, while the open green squares denote the measurement obtained from the Gaussian fit, relative to the continuum. Shown for comparison are the measurements around 2010 reported by Chernyakova et al. ( 2014 ) (red crosses). As with the Hα line, the He i line shows a general increase in the absolute equivalent width which peaks after periastron, though the growth is not as great. The variation in the strength of the line is consistent with the variability observed in the Hα line. 3.2.2 V/R In general, the violet component of the double peaked He i line is more dominant, as is seen in the equivalent width | W λ | of the violet component and the ratio of peaks of the violet to red (V/R) components. The V/R variation (Fig. 4 c) has been measured from the ratio of the heights of the Gaussian fits to the Violet and Red component of the He i line. The height is measured relative to the continuum and the error is given by the statistical error of the fit. Around the first disc plane crossing, there is a marked increase in the asymmetry of the line, while there is a decrease in V/R around periastron and a small increase in the red component around the second disc plane crossing. This clearly illustrates the asymmetry of the He i line and its variation around periastron. The V/R variation lies between 0.93 V/R 1.65 during the observed period. 4 DISCUSSION Around periastron the equivalent width of the Hα line smoothly increased to a maximum of −72.7 ± 0.7 around ∼τ + 13 d, after which it decreased to values consistent with the pre-periastron levels. The equivalent widths after ∼τ + 13 d are consistent with the previous periastron passage (Chernyakova et al. 2014 ) but appear to be consistently lower before this. This is clearly seen before periastron where the average equivalent width (and error) of the Hα line was −62.9 ± 3.1 Å in 2010, but −56.7 ± 0.6 Å in 2014. We interpret this as being due to variability in the Be star circumstellar disc which could well change from periastron to periastron. This may imply that the mass of the circumstellar disc was lower before the 2014 periastron passage (as compared to the 2010 periastron passage). Since the circumstellar disc influences the shock front around the pulsar, the differences in the circumstellar disc properties will be an important contributing factor to the variations in the multiwavelength emission observed around different periastra. There is also a marked change in the disc around the time of the first disc plane crossing (τ − 17.5 d), as is noted by the increase in the
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