1988 December 15. Received 1988 December 14; in original form 1988 October 11'
title: 'Pulsations in B-type supergiants with masses $M<20M_\odot$ before and after core helium ignition'
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stars: early-type – stars: supergiants – stars: oscillations

Introduction
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Slowly Pulsating B-type supergiants (SPBsg) have emerged as a new class of pulsating variables after Saio et al. (2006) have detected pulsational frequencies in the MOST satellite data of the blue supergiant HD 163899 (B2 Ib/II, Klare & Neckel 1977, Schmidt & Carruthers 1996). Saio et al. (2006) identified 48 frequency peaks in the MOST light curve and attributed them to g- and p-mode pulsations. Because so far only one object of this type is found, the SPBsg class is not yet well defined as for the range of effective temperature and luminosity. Also the evolutionary status of these pulsators remains unrevealed; they may be either in the shell hydrogen burning phase as well as after core helium ignition. The finding of Saio et al. (2006) has prompted a few groups (Godart et al. 2009, Daszyńska-Daszkiewicz, Ostrowski, Pamyatnykh. 2013; hereafter D2013) to reanalyse pulsation stability in models of B-type stars after the Terminal Age Main Sequence (TAMS) and to further studies 