ESTUDO ESPECTROSCÓPICO DE ESTRELAS CANDIDATAS A ESTRELAS CARBONADAS QUENTES

Abstract

Abstract Carbon stars constitute a vast and interesting class of chemically peculiar stars which has carbon overabundance relative to oxygen. This class of stars was first identified by Secchi (1868) and is characterized by the presence of the molecular bands C2, CH, and CN. The study of the chemical composition for these stars is interesting because it can help to understand the chemical evolution of the Galaxy and also for the mathematical modelling used in stellar evolution theory, as well as to give information about how these objects can contribute to the interstellar medium enrichment and the composition of the next generations of stars. In this work, we conducted a study using high resolution spectroscopy for a sample of four carbon stars candidates. These stars are: HD 36598, a CH star candidate, and HD 95405, HD 29154 and BD-16 1217, C-R stars candidates. This work aims to analyze the abundance pattern of the stars above mentioned. Therefore, we first determined the atmospheric parameters for the stars of the sample using atmosphere models from Kurucz (1993) and the the spectral synthesis MOOG code. The atmospheric parameters found are between 4660K ≤ Teff ≤ 4770K, 2.1 ≤ log g ≤ 2.5, 1.3kms−1 ≤ ξ ≤ 1.5kms−1, and the metallicity is between −0.34 ≤ [Fe/H] ≤ +0.08. Thus, we determined the chemical abundances using two methods: equivalent width measurements, for the elements Na, Mg, Al, Si, Ca, Ti, Cr, Ni, Sr, Y, Zr, Ce, Nd, and Sm, and spectral synthesis, for CNO contents (including the 12C/13C isotope ratios), Li, Rb, Eu, and Nb. Moreover, we also determined the masses and luminosities for the stars in the sample. The results indicate that all these stars have luminosities similar to giant stars. With regarding the derived abundances, only the HD 36598 star has a C/O ratio higher than the unit. This star also has an overabundance of s-process elements, being classified as a CH star. Therefore, HD 36598 is the only star in the sample that agrees with the classification in the literature. The HD 29154 and BD-16 1217 stars were classified as strong-CN, which are stars that show an abundance (C + N) greater than in the Sun. Finally, from the results for HD95405 star, we suggest that could be a merger between a normal giant and a carbon white-dwarf or even an oxygen giant in transition to a carbon star, however, its classification remains an unknown.