Testing the hot-flasher scenario with asteroseismological tools: first results

MILLER BERTOLAMI, M. M.; CÓRSICO, A. H.

rio de Janeiro, Brasil

Congreso; XXVII IAU General Assembly; 2009

IAU

Hot subdwarf  stars are  an important population  of faint  blue stars that can  roughly be grouped  into two families,  the sdB and  the sdO stars. sdBs (which are cooler  than sdOs) are characterized by spectra that  lack  of  helium lines,  or,  at  most,  show only  weak  helium signatures.   The sdO  stars, on  the other  hand, have  higher helium abundances and can even be dominated by helium. sdO and sdB stars have been identified  with stars populating  the hot end of  the horizontal branch  (HB)  of some  globular  and open  clusters  (de  Boer et  al. 1997). While the sdBs constitute an homogeneous spectroscopic class, a large variety  of spectra  is observed among  sdO stars (Lemke  et al. 1997).   This diversity  of  spectra, along  with the  helium-enhanced surface abundances observed  in many of these stars,  pose a challenge to  our understanding of  stellar evolution.   As a  consequence, some non-canonical  evolutionary  scenarios   must  be  invoked  for  theirformation. Among  them (see  Heber 2009 for  a review), a  core helium flash after the departure from the red giant branch (i.e. "hot-flasher scenario")  offers one of  the most  promising explanations  for their origin.