Hints of the Existence of C-rich Massive Evolved Stars

Quintana Lacaci, G., Cernicharo, J., Agundez, M., Fonfria, J. P., Velilla Prieto, L., Contreras, C. S., Bujarrabal, V., Castro Carrizo., Alcolea, J. 2019. Hints of the Existence of C-rich Massive Evolved Stars. Astrophysical Journal 876, 2, DOI: 10.3847/1538-4357/ab133e

We aim to study the properties of a particular type of evolved stars, 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 = 2-1. emission 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-circle dot). =. 4.1 and 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. x. 10(-5)-6. x 10(-3)M(circle dot) yr(-1)) suggest that while IRC+ 10401 might be an AGB star, AFGL 2233 could be an 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 similar to 5-9M(circle dot). which could correspond to an AGB or an RSG and AFGL 2233 an RSG with M-init similar to 20M(circle dot), which would confirm the existence of massive C-rich evolved stars. Two scenarios are proposed to form these types of objects. The first one is capable of producing high-mass AGB stars up to similar to 8M(circle dot). and the second one is capable of forming C-rich RSGs like AFGL 2233.

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