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Astron. Astrophys. 353, 163-176 (2000)


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Checking the yellow evolutionary void

Three evolutionary critical Hypergiants: HD 33579, HR 8752 & IRC +10420 *

H. Nieuwenhuijzen and C. de Jager

SRON Laboratory for Space Research; Sorbonnelaan 2, 3584 CA Utrecht, The Netherlands and Astronomical Institute, Utrecht, The Netherlands

Received 21 December 1998 / Accepted 25 August 1999

Abstract

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 [FORMULA] and a decrease of the atmospheric acceleration to [FORMULA] [FORMULA] zero. Thereafter [FORMULA] and [FORMULA] 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.

Key words: stars: supergiants – stars: atmospheres – stars: mass-loss – stars: evolution – gravitational waves

* Based on observations at the La Palma Observatory and the ESO Observatory in Chili.

Send offprint requests to: H. Nieuwenhuijzen (H.Nieuwenhuijzen@sron.nl)

© European Southern Observatory (ESO) 2000

Online publication: December 8, 1999

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