2000A&A...357..581N

We present results of a detailed analysis of spectral variability observed in the optical spectrum of HD 4004 (WR1). On the basis of data obtained during monitoring of this object on 3 consecutive nights in Dec 1993, and two additional nights in Dec 1994 we show that the variability in HeII λ 5411, CIV λ 5808 and HeI λ 5876 may reach as much as 50% in equivalent width. This variability shows a systematic, gradual character, which justifies a search for periodicity. We show that the observed spectral-line-profile changes may mimic radial velocity variations but that any real radial velocity variations in the observed lines of HD 4004 are small. Our search for periodicity in the data was unsuccessful: the data do not show periodicities within the time covered by the observations (∼2 days). Our data suggest, however, the existence of a longer-term variability pattern. We show that the observed pattern of the Temporal Variance Spectrum in different lines can be qualitatively understood in terms of stratification.