Highlights - Volume 489-3 (October III 2008)

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HIGHLIGHTS: this week in A&A

Volume 489-3 (October III 2008)

 


In section 2. Astrophysical processes

“The impact of type Ia supernovae on main sequence binary companions”, by P. Pakmor et al., A&A 489, p. 943

Type Ia supernovae show no hydrogen in their spectra, but the canonical single-degenerate progenitor scenario does involve a hydrogen-rich companion star next to the exploding white dwarf. This paper shows that less hydrogen may be stripped off a main sequence companion star during the explosion than previously thought, with the consequence that single-degenerate SNIa explosions would no longer be thought to contradict observations.  

 



In section 1. Letterts

“Lithium depletion and the rotational history of exoplanet host stars”, by J. Bouvier, A&A 489, p. 57

Solar-type stars with planets are known to be depleted in lithium on average compared to stars without a convection that brings it to the star's core where the temperatures are high enough. As a consequence, since stars with giant planets presumably had disks that were more massive and/or lasted longer, one would expect that they would have received more fresh lithium, which seems to contradict the observations. In this issue, Bouvier shows, however, that another parameter should be taken into account: the star's rotation. In the Pleiades cluster, young stars that are fast rotators tend to have less lithium than stars that rotate slowly. Bouvier presents a model that reproduces the evolution of rotation observed in clusters, based on the hypothesis that fast rotators exchange angular momentum more efficiently than stars that rotate more slowly. As a consequence, slow rotators have more shear, hence are expected to mix the lithium in the envelope with the star's deeper layers more efficiently. This explains the Pleiades observations. The fact that stars with planets are depleted in lithium thus indicates that they were rotating slowly, therefore that they were braked by a long-lived circumstellar disk. From this, Bouvier concludes that long-lived disks may be a necessary condition for giant planet formation.  
In section 7. Stellar structure and evolution

“The temporal changes of the pulsational periods of the pre-white dwarf PG 1159-035”, by J.E.S. Costa and S.O. Kepler, A&A 489, p. 1225

This paper reports the first measurement of radius evolution from a change in the rotational frequency of a cooling post-AGB star. Anomalously rapid changes in the rotation period are obtained from the power spectrum analysis of large number of pulsational modes (with 10% uncertainty), implying a change in the radius of the envelope and temperature that are more rapid and larger than currently predicted by evolutionary models of cooling post-AGB stars.  

 

© Astronomy & Astrophysics 2008