Stability boundaries for massive stars in the sHR diagram
  Stability boundaries of radial pulsations in massive stars are compared with positions of variable and non-variable blue-supergiants in the spectroscopic HR (sHR) diagram (Langer & Kudritzki 2014), whose vertical axis is $4\log T_{\rm eff}-\log g \,(= \log L/M)$. Observational data indicate that variables tend to have higher $L/M$ than non-variables in agreement with the theoretical prediction. However, many variable blue-supergiants are found to have values of $L/M$ below the theoretical stability boundary; i.e., surface gravities seem to be too high by around 0.2-0.3 dex. 
Hideyuki Saio, Cyril Georgy, Georges Meynet
astro-ph.SR