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The enigmatic WR46: A binary or a pulsator in disguise. I. The photometry
We discuss the observational history of the Wolf-Rayet object WR 46(WN3p), including a re-investigation of the original discovery platesfrom early this century. We find that the reported presence of N Iiilines is a mis-interpretation of N V lines and conclude that the objectdid not change its spectral type since the first recording one centuryago. We performed photometric monitoring in the period 1986-1999, andconfirm that the object shows cyclical variability on a time scale ofhours. The shape of the light curves varies from purely sinusoidal toirregular, and from an amplitude of nearly 0\fm1 to constancy. Inaddition, night-to-night variability of the mean brightness causesfolded light curves to display a large scatter. We investigate thefrequency behaviour of the photometric data. From the periodograms ofour two large data sets, in 1989 and in 1991, we identify frequencies ofsignificantly different values 7.08 cd-1 and 7.34cd-1, respectively. Moreover, the 1989 data show strongevidence for an additional frequency fx= 4.34cd-1. The periodograms of our eight smaller data sets showmore ambiguous behaviour. We discuss whether these latter data showevidence for multi-frequency behaviour, or whether they can bereconciled with a single clock with a changing clock-rate. As pointedout by van Genderen et al. (1991), if the data are folded using twicethe single-wave period, the light curves appear ellipsoidal with unequalminima. Although the difference in depth of the minima is hardlysignificant, it does occur in both large data sets. Moreover, thesimultaneously obtained radial velocity measurements are in betteragreement with the double-wave than the single-wave period (Paper II).Finally, Marchenko et al. (2000) observed WR 46 to have a single-waveperiod of the same order as the double-wave period identified here. Theperiodograms of the (V-W) colour index show that the colour changes arecontrolled by single-wave frequencies, or their sub-harmonics(double-wave periods), but not by fx. The colour variation ofWR 46 is peculiar in the sense that the object is red when bright andblue when faint. Although the spectrum of WR 46 has been suggested tooriginate from a stellar disc, this peculiar colour behaviour is in linewith its WR nature, which is also confirmed by its spectral variability(Marchenko et al. 2000; Paper II). In addition, our seasonal photometricaverages of WR 46 show a rise from 1989 to 1991 of 0.12m, confirming thebrightening detected by the Hipparcos-satellite (Marchenko et al. 1998).Eventually, WR 46 brightened by about 0.25m and subsequently declined ona time scale of years. Such a rise is unique among the WR stars in theHipparcos-survey, and has not been found anywhere else. We investigatethe changes to the double-wave behaviour and mean colour-indexcoinciding with the period change and brightening. Interpretation of theobject as either a multi-frequency non-radial WR pulsator, or a WRbinary with possible large orbital decay is deferred to Paper III.Largely based on observations collected at the European SouthernObservatory (ESO), La Silla, Chile.
| A homogeneous catalog of new UBV and H-beta photometry of B- and A-type stars in and around the Scorpius-Centaurus OB association
B- and A-type stars in and near the Sco-Cen OB association areinvestigated with UBV and H-beta photometry to acquire data relevant tothe luminosity function of Sco-Cen. The measurements generally consistof two 10-s integrations of U, B, V, (W, N) filters, and theobservations are corrected iteratively for atmospheric extinction andinstrumental response. The data presented give the mean V magnitude,mean B-V, mean U-B, and the estimated uncertainties for these values.The catalog provides a homogeneous catalog of data for a large fieldwith stellar objects delineating membership to the association Sco-Cenand that affect the luminosity function of the aggregate.
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