Wind inhomogeneities in Wolf-Rayet stars. IV. Using clumps to probe the wind structure in the WC8 star HD 192103

We present the most intensive, high-quality spectroscopic monitoring of opt ical Wolf-Rayet emission lines ever obtained. The Wolf-Rayet star HD 192103 (=WR 135; subtype WC8) was observed in the 5650-5840 Angstrom regime alter nately from both the William Herschel Telescope and the Canada-France-Hawai i Telescope. The final data consist of a series of 197 spectra spread over 64 hr, each with a resolving power lambda/Delta lambda similar or equal to 20,000 and a signal-to-noise ratio in the continuum similar or equal to 450 per 3 pixel resolution element. We clearly and unambiguously identify stoc hastic, structured patterns of intrinsic variability at the 1%-2% level of the line flux in the broad C In lambda 5695 emission line. The lambda 5801/ 12 doublet emission is also found to be variable at the 0.2%-0.5% level of the line flux. We find a correlation between the variability patterns obser ved in C III and C rv, which suggests a significant overlap in the emission volumes of these transitions, although C Iv is known to arise somewhat clo ser to the star. We attempt to reproduce the observed line profile variatio n patterns using a simple phenomenological model, which assumes the wind to be fully clumped. With a minimal set of assumptions, we are able to reprod uce both the shape and the variability in the C III lambda 5696 emission pr ofile. We show that the variability pattern provides constraints on the rad ial extent of WR 135's wind where C III is produced, as well as on the loca l wind acceleration rate. However, our simple clump model does not reproduc e the lower variability in the C rv doublet unless we assume the C Iv emiss ion to occur in a much larger volume than C III, implying that: significant C Iv emission occurs farther out in the wind than C III. We suggest that w hile some C Iv emission might occur farther out, possibly because of reioni zation from shocks, a more likely explanation is that wind clumping signifi cantly increases with distance from the star, leading to larger variability levels in C III, formed farther out than most of C rv. Alternatively, opti cal depth effects and/or local ionization gradients within clumps could con spire to attenuate clumping effects in the C rv emission line while enhanci ng them in the C III line.