BVRI Photometry of CX Cephei (WR 151)

摘要

The CX Cephei system is a double-line spectroscopic, eclipsingbinary, consisting of an 05V and a WN5 (Woft-Rayet star) component. It hasthe second shortest known period (2.12691d) among O + WR binaries. Theprimary eclipse is shallow (approx. 0.1 magnitude) and the secondary eclipseeven shallower. There is other variability also, accounting for a total range ofapprox. 12.0 to 12.2 in Lipunova and Cherepashchuk 1982 (Soy. Astron. 26,45-53) published photometry data from the 1980's. Lewis et al. 1996 (ApJ405, 312-326) published radial velocity data, showing that the WR star is infront at primary minimum. To this we add 340+ BVRI points over two yearsfrom the Sonoita Research Observatory (SRO), plus assorted time seriesfrom Sonoita (by HQA) and from Starhouse Observatory (by KMP). Fromour observations, we were able to, 1) refine the period given by Lipunova andCherepashchuk, and show that, 2) there is intrinsic variability in addition tothe eclipsing binary light curve, 3) that, unlike the 1980s, the secondary eclipseis now barely detectable, 4) there may or may not be additional "structure" inthe eclipsing light curve, 5) and that the light curve varies with color. We seethat the minima are pointed (eclipse not total), that the minima have a distinctbeginning and end, although there are "shoulders" (ellipticity is important, butsky is seen between the stars at quadrature), that the eclipses are very shallow(low i, barely eclipsing). There is a dimward slope between phase 0.2 and 0.8,ranging from 2.5% in flux in B and V, to less than I% in I. It seems unlikely thatthe WR core is substantially cooler than even an 05, so the primary minimumis expected to be at least partly an "atmospheric" eclipse caused by the WRwind (as Lipunova and Cherepashchuk modeled it), rather than the star itself.However, the primary minimum is one of the most stable features with time,so the wind opacity and configuration must not be responsible for observedchanges. Changes in the secondary minima must be due to changes in whatthe 05 is eclipsing. We have not yet modeled all this!