Spectral energy distributions of O-type stars.

Abstract

Narrow-band photoelectric spectrum scanner observations of the spectral energy distributions of O and Of stars are presented. After the application of reasonable reddening corrections it is found that both Of and ordinary O stars present evidence for effects of atmospheric extension. These effects are seen primarily in the flatness of the energy distribution which is most extreme in the hottest Of stars. Model atmospheres (dynamic or static) which produce only minor observable effects of extension are therefore ruled out.

Spectrophotometry using an intensifier silicon vidicon.

“…The spectrum was then corrected for differential extinction. Plotted points are from Kuan and Kuhi (1976). The agreement between these points and our plot is, in general, quite good.…”

“…Fig. 3-The spectrum of 9 Sge, on an absolute flux scale, using the photometry of Kuan and Kuhi (1976).…”

“…We have also estimated the extent of the lines N in (463.4nm) and He n (468.6 nm) as shown in Figure 4. Table II gives the measured strengths of features in the spectrum using both the observed and de- reddened fluxes given by Kuan and Kuhi (1976) to calibrate the spectrum. We present these data as an example of the type of analysis that may be applied to spectra obtained using multichannel techniques.…”

“…A spectrum of such quality of the Of star 9 Sge is presented. The absolute photometry of Kuan and Kuhi (1976) obtained for several points in the spectral region 420-560 nm has been used for calibration and allows absolute measurements of line strengths to be made.…”

Line profile variability in the spectra of Oef stars

“…Subsequent investigations revealed however that flat energy distributions are common among Of stars and can be attributed to the effect of atmospheric extension (see e.g. Kuan & Kuhi 1976).…”