Microvariability of Line Profiles in the Spectra of OB Stars II: $\delta $Ori A

Abstract

We have studied variability of the spectral lines of the OB star $\delta $Ori A--the brightest component of the $\delta $Ori triple system. Forty spectra with signal-to-noise ratios $\approx$500--800 and a time resolution of four minutes were obtained. We detected variability in the HeII$ \lambda 4686$, HeI$ \lambda $4713 and H$\beta$ absorption and the CIII$ \lambda $5696 emission line profiles. The amplitude of the variability is $\approx$(0.5--1)% of the continuum intensity. The dynamical wavelet spectrum of the profile variations reveals large-scale components in the interval 25--50 km/s that move within the -$V\sin i$ to $V\sin i$ band for the primary star of the system, Aa$^1$, with a band crossing time of 4$^h$--5$^h$. However, some of the variable features go outside the band, presumably due to either imhomogeneities in the stellar wind from $\delta $Ori Aa$^1$ or non-radial pulsations of the weaker components of the system, Aa$^2$ or Ab. The detected variability may by cyclic with a period of $\approx 4^h$ . We suggest that it is associated with non-radial pulsations of the primary in the sector mode $(l, m)=(2,-2)$.