Hunting Very Massive Metal-poor Stars. Danny Lennon (ESA-STScI)
The IMF stops at ~60 solar masses and a star’s evolution is determined by its initial mass and metallicity....simple.
Stars have initial masses up to at least ~300 solar masses and ....it’s complicated!
Hunter & Brott
Most are not single
FUSE and now COS
Spitzer & JWST
COS & STIS
Evolution and final fate of Massive Stars
Courtesy: Adi Pauldrach
Hubble has pioneered the investigation of radiation driven winds at low Z. In the SMC roughly 30 observed with STIS (Lennon: opposite), another 20 with COS (Hubeny & Lanz: not yet published).
COS enables us to push into the “weak wind” regime at lower luminosities and masses.
By contrast there are only ~10 such spectra for the LMC
From FUSE there are ~100 good quality spectra for each galaxy.
Courtesy: Miriam Garcia
The sensitivity of COS allows us to investigate massive stars in galaxies out to ~1 Mpc and sample star forming irregular galaxies more metal poor than the LMC (0.5 solar) and SMC (0.2 solar). Examples include IC1613 (Garcia: 9 stars in IC1613, opposite) and WLM (Lanz: 2 in IC1613, 1 in WLM, yet to be observed). Both galaxies have [O/H] ~ 0.1 solar.
Sana et al 2012
HST/STIS - Crowther et al
HST/FOS - Massey & Hunter
WFC3 Image: E. Sabbi