Vol. 543
In section 7. Stellar structure and evolution

Hot subdwarf stars in close-up view. II. Rotational properties of single and wide binary subdwarf B stars

by S. Geier and U. Heber, A&A 543, A149


This paper represents an important contribution to our understanding of extreme horizontal branch stars. After investigating the rotational properties of hot subdwarf stars in close binary systems where synchronized rotation is the norm, the authors have now extended their investigations of the rotation states to isolated objects (either singles or components of wide binary systems). They found that isolated subdwarfs are all slow rotators, with quite a narrow distribution of Vsini of about ~8 km/s. Furthermore, they show that there are no differences between the distribution of Vsini for single stars and that for components of wide binaries. The authors suggest a plausible connection with the hot HBB stars, which are also slow rotators. These results are at odds with the prediction that single hot subdwarfs should have been formed primarily by the merger of two helium white dwarfs, in which case the sdB products should show fairly high rotation velocities.