SPECTRAL-ANALYSIS OF THE HIGH-GRAVITY EXTREME HELIUM STAR LSIV-DEGREES-2(6)

The optical spectrum of the early B hydrogen-deficient star LS IV + 6 degrees 2 has been analysed. With T-eff = 31 000 K, log g = 4.05 n(H) similar to 10(-4) and n(C) similar to 0.1 (relative abundances by numb er), it is the hottest high-gravity extreme helium star (EHe) yet stud ied. The He I spectrum shows all predicted permitted and forbidden tra nsitions in absorption. LS IV + 6 degrees 2 is a comparatively metal-r ich EHe star; abundances of C, N, O, Ne, Mg, Al and P are typical of o ther EHes, whilst Si and S are somewhat deficient. With the surface pa rameters given, LS IV + 6 degrees 2 lies close to the boundary of the helium star pulsation instability finger near T-eff similar to 27 000 K. Available data indicate that the radial velocity is variable, but g ive no indication of amplitude or period.