Документ взят из кэша поисковой машины. Адрес оригинального документа : http://www.stsci.edu/institute/conference/may_symp/supportingFiles/poster99 Дата изменения: Mon May 8 23:32:56 2006 Дата индексирования: Sun Dec 23 08:57:01 2007 Кодировка: Поисковые слова: astro-ph

Detection of Wolf-Rayet stars in host galaxies of Gamma-Ray Bursts (GRBs): are GRBs produced by runaway massive stars ejected from high stellar density regions ?
Daniel Schaerer (ObsGeneva), F. Hammer, H. Flores (ObsParis), M. Dessauges (ObsGeneva), , E. Le Flo'ch (Arizona)

Main objectives: · Basic test of collapsar model: search for Wolf-Rayet (WR) stars in long GRB hosts, as WR stars are expected progenitors of collapsars · Determine metallicities and stellar populations of GRB host galaxies and environment of long GRB · constrain progenitor models ...

RESULTS from deep FORS2/VLT spectroscopy: · WR features (WN in all and WC in 1 galaxy) found in 3 nearest GRB host galaxies ! Corresponds to ~100-200 WR stars!! --> previous non-detections due to insufficient depth · Detection of young massive Super Star Clusters (SSC) with ~ 1000-2000 O7V stars ==> Very clear association of long GRB with WR!!

RESULTS HST imaging + spectroscopy: · GRB980425: GRB located ~800 pc away from massive SSC in region with <~10 O7V stars ! However, from small GRB/SNII branching ratio (few times 10-3) the GRB is expected to occur in region with large number of massive stars. ==> Suggestion: GRB progenitor ejected ~2-3 Myr ago from nearby SSC! This «runaway» ejection leads possibly to special conditions (rotation...) --> GRB. Rare kinematical event explains naturally small fraction of GRBs among massive stars. · Spatial shift (~300-800 pc) also found for 2 other nearby GRB hosts and compatible with HST imaging of larger sample (Fruchter
et al. 2006, astro-ph/0603537)

For more details see: Hammer et al. 2006 (A&A in press) --> astro-ph/0604461