2000A&A...353..163N

We have checked the reality of the yellow evolutionary void (which is an area in the Hertzsprung-Russell diagram where atmospheres of blueward evolving super- and hypergiants are moderately unstable), by comparing one star inside the void: HD 33579 (= R76), and two at the low-temperature border of it: HR 8752 (= HD 217476, V509 Cas) and IRC+10420. We found that the first star has a large mass and a fairly stable behaviour over time. These aspects suggest, together with abundance determinations by others, that it is a fairly young, still redward-evolving supergiant. For such a star the void is not forbidden. The two other stars, HR 8752 resp. IRC+10420, have low masses which places them in the post-red blueward loop. They show indications of the expected bouncing effect for blueward returning red supergiants: when approaching the void they eject mass, resulting in a sudden reduction of T_eff and a decrease of the atmospheric acceleration to g_eff≃zero. Thereafter T_eff and g_eff increase again. For HR 8752 two such recent `bounces' have been identified. The photometric variations of HR 8752 and of HD 33579 are due to high-l gravity-wave pulsations.