S 18 : a new B(e) supergiant in the Small Magellanic Cloud with evidence for an excretion disk.

In 1987 we obtained high dispersion, high signal-to-noise spectra of the peculiar emission-line star S 18 in the SMC UBVRIJHK(L) magnitudes were also measured. Its line spectrum is distinguished by a forest of narrow emission lines (FWHM of 20 to 60 km s^-1^) of singly ionized (Si II, Ti II, V II, Cr II, Ni II, and Fe II) and neutral (Fe I, Ca I) metals. Likewise, forbidden emission lines of [Fe II], [S II], and [O I] were identified. A broad emission feature at λ6159 A is identified as a Tio band. We find this same emission feature in the red spectra of other B[e] supergiants. The spectrum of S 18 is further characterized by broad P Cyg-type profiles (v_term_ ~ 750 km s^-1^) of H I and He I. On the other hand, the He II λ4686 line, although strong in previously published spectrograms is definitely not present in our spectrogram. The photometric data combined with published IUE observations can be explained by adopting a Kurucz model with T_eff_ = 25000 K and log g ~ 3 and an IR excess due to ff-fb and dust radiation. From both the hybrid line spectrum and the continuum-energy distribution we conclude that S 18 is a further example of a B[e] supergiant with a high velocity CAK-wind in the polar region and a slow, much denser (~ 10^3^ x) wind in the equatorial region forming an excretion disk. The variable He II-line strength and its complete disappearance is discussed on the basis of our excretion-disk model of S 18 plus a companion.