Abstract
We aim at studying the properties of a particular type of evolved stars, the C-rich evolved stars with high expansion velocities. For this purpose we have focused on the two best studied objects within this group, IRC +10401 and AFGL 2233. We focused on determining their luminosity by studying their spectral energy distribution. Also we have obtained single-dish line profiles and interferometric maps of the CO J=1-0 and J=2-1emission lines for both objects. We have modeled this emission using a LVG radiative transfer code to determine the kinetic temperature and density profiles of the gas ejected by these stars. We have found that the luminosities obtained for these objects (log(L/L (⊙)) = 4.1 & 5.4) locate them in the domain of the massive Asymptotic Giant Branch stars (AGBs) and the Red Supergiant stars (RSGs). In addition, the mass-loss rates obtained (1.5 × 10(-5) - 6 × 10(-3) M (⊙) yr(-1)) suggest that while IRC+10401 might be an AGB star, AFGL 2233 could be a RSG star. All these results, together with those from previous works suggest that both objects are massive objects, IRC +10401 a massive evolved star with M (init) ~ 5 - 9M (⊙) which could correspond to an AGB or a RSG and AFGL 2233 a RSG with M (init) ~ 20M (⊙), which would confirm the existence of massive C-rich evolved stars. Two scenarios are proposed to form these types of objects. The first one capable of producing high mass AGB stars up to ~ 8M (⊙) and a second one capable of forming C-rich RSGs as AFGL 2233.