The Li overabundance of J 37: diffusion or accretion?

Abstract

In September 2002 the discovery of a super Li-rich F-dwarf (J 37) in NGC 6633, an iron poor analogue of the better studied Hyades and Praecepe open clusters, was announced. This unique star was thought to be the smoking gun for the action of diffusion, models of which predict a narrow “Li-peak” at approximately the correct temperature. However, with more detailed studies into J 37's abundance pattern this star provides firm evidence for the accretion of planetesimals or other material from the circumstellar environment of new born stars.

Thanks to the specific predictions made about the behaviour of Be abundances, (the most striking of which being no Be in super-Li-rich dwarfs subject to diffusion) the opposing diffusion/accretion predictions can be tested.

Initial modelling of the Be line indicates that J 37 is as Be rich as it is Li rich; $\log N({\rm Be}) = 2.25 \pm 0.25$, and so is broadly consistent with an accretion-fuelled enhancement. However, that both Li and Be are enhanced by much more than the iron-peak elements (as determined in previous studies) suggests that diffusion also plays a role in increasing the abundances of Li and Be specifically.

Furthermore, a new data set from the UVES/UT2 combination has allowed the elemental abundance of iron to be measured. The preliminary stellar parameters are; $T_{\rm eff} \sim 7340\,{\rm K},\log g \sim 4.1$, microturbulence $\sim 4.3 {\rm km s^{-1}}, [{\rm Fe}/{\rm H}] \sim 0.50$. This again provides distinct evidence for the effects of accretion in J 37 and requires a new synthesis of the Be doublet.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html