Published online by Cambridge University Press: 12 April 2016
The main characteristics of the LBVs with “normal” S Dor-type outbursts are reviewed. At quiescence they are luminous (MBol ≈ −9 to −10) OB supergiants (14 000 K ≲ Teff ≲ 30 000 K) occupying an inclined instability strip in the HRD. The most luminous S Dor variables are the hottest ones. During outburst dense envelopes are expelled of equivalent spectral type middle A to early F. S Dor variables occupy at maximum a vertical strip in the HRD at T≈8000 K. The observed amplitudes in the visual range increase from 1 mag (e.g. R71; Teff = 14500 K at quiescence) to 2.5 mag (e.g. R127; Teff = 33000 K at quiescence). The existence of an amplitude-luminosity relation is suggested which can be used to derive extragalactic distances.