Instability regions in the upper HR diagram |
| |
| Authors: | Cornelis de Jager Alex Lobel Hans Nieuwenhuijzen Richard Stothers |
| |
| Institution: | 1SRON Laboratory for Space Research, Sorbonnelaan 2, 3584 CA Utrecht, the Netherlands;2Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA;3Goddard Institute for Space Studies, NASA, 2880 Broadway, New York, NY 10025, USA |
| |
| Abstract: | The following instability regions for blueward evolving-supergiants are outlined and compared. (1) Areas in the Hertzsprung–Russell (HR) diagram where stars are dynamically unstable. (2) Areas where the effective acceleration in the upper part of the photospheres is negative, hence directed outward. (3) Areas where the sonic points of the stellar winds (where  are situated inside the photospheres, at a level deeper than  . We compare the results with the positions of actual stars in the HR diagram and we find evidence that the recent strong contraction of the yellow hypergiant HR 8752 was initiated in a period during which  , whereupon the star became dynamically unstable. The instability and extreme shells around IRC+10420 are suggested to be related to three factors:  the sonic point is situated inside the photosphere; and the star is dynamically unstable. |
| |
| Keywords: | stars: atmospheres stars: evolution Hertzsprung–Russell (HR) diagram stars: interiors supergiants |
|
|
