New ultraviolet (λ ≃ 1300 Å, λ ≃ 3400 Å), HST Faint Object Camera observations have been used to derive the UV color-magnitude diagram (CMD) of R136. The main scientific goal is the study of the upper end of the stellar mass function at ultraviolet wavelengths where the color degeneracy encountered in visual CMDs is less severe. The CMD has been compared to a set of theoretical isochrones, which have been computed using the latest generation of evolutionary models and model atmospheres for early-type stars. Wolf-Rayet stars are included, and their emergent fluxes are calculated with the theoretical continuum energy distributions of Schmutz et al. Comparison of the theoretical and observed CMD suggests that there are no stars brighter than M 130 ≃ -11. We use the observed main sequence turnoff and the known spectroscopic properties of the stellar population to derive constraints on the most probable age of R136. The presence of WNL stars and the lack of red supergiants suggests a most likely age of 3 ± 1 Myr. A theoretical isochrone of 3 ± 1 Myr is consistent with the observed stellar content of R136 if the most massive stars have initial masses around ≃50 M ⊙.
The population of massive stars in R136 from Faint Object Camera ultraviolet observations
Ragazzoni R.;BARBIERI, CESARE
1993
Abstract
New ultraviolet (λ ≃ 1300 Å, λ ≃ 3400 Å), HST Faint Object Camera observations have been used to derive the UV color-magnitude diagram (CMD) of R136. The main scientific goal is the study of the upper end of the stellar mass function at ultraviolet wavelengths where the color degeneracy encountered in visual CMDs is less severe. The CMD has been compared to a set of theoretical isochrones, which have been computed using the latest generation of evolutionary models and model atmospheres for early-type stars. Wolf-Rayet stars are included, and their emergent fluxes are calculated with the theoretical continuum energy distributions of Schmutz et al. Comparison of the theoretical and observed CMD suggests that there are no stars brighter than M 130 ≃ -11. We use the observed main sequence turnoff and the known spectroscopic properties of the stellar population to derive constraints on the most probable age of R136. The presence of WNL stars and the lack of red supergiants suggests a most likely age of 3 ± 1 Myr. A theoretical isochrone of 3 ± 1 Myr is consistent with the observed stellar content of R136 if the most massive stars have initial masses around ≃50 M ⊙.
Pubblicazioni consigliate
I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
