2016/07/24 by Takashi Tsuji · 10 citations
Chemistry · Physics and Astronomy · #Astronomy #Astrophysics #Astrophysics and Star Formation Studies #Atomic physics #Brown dwarf #Carbon-12 #Galaxy #Infrared #Interstellar medium #Line (geometry) #Nuclear reaction #Physics #Spectral line #Spectroscopy #Spectroscopy and Laser Applications #Stars #Stellar classification #Stellar, planetary, and galactic studies #astro-ph.SR
paper · pdf · doi:10.1093/pasj/psw076
published in Publications of the Astronomical Society of Japan 68(5) (Oxford University Press) · 19 pages, 6 figures, 5 tables, accepted by PASJ
arxiv created 2016/07/24 · openalex created_date 2016/09/16 · openalex publication_date 2016/09/23 · arxiv updated 2016/09/28 · openalex updated_date 2026/08/05
Abstract Carbon isotopic ratios are estimated in 48 M dwarfs based on the medium resolution near infrared spectra (λ/Δ λ ≈ 20000) of the 13CO (3,1) band. We find clear evidence for the presence of a 13CO feature for the first time in the spectra of M dwarfs. Spectral resolution of our observed data, however, is not high enough to analyze the 13CO feature directly. Instead, we compare the observed spectrum with synthetic spectra assuming 12C/13C = 10, 25, 50, 100, and 200 for each of 48 M dwarfs and estimate the best possible 12C/13C ratio by chi-square analysis. The resulting 12C/13C ratios in M dwarfs distribute from 39 to a lower limit of 200. The mean value of 31 M dwarfs for which 12C/13C ratios are determined (i.e., excluding those with the lower limit only) is (12C/13C)dM = 87 ± 21 (p.e.), and that of 48 M dwarfs including those with the lower limit of 200 is (12C/13C)dM > 127 ± 41 (p.e.). These results are somewhat larger than the 12C/13C ratio of the present interstellar matter (ISM) determined from the molecular lines observed in the millimeter and optical wavelength regions. Since the amount of 13C in the ISM has increased with time due to mass loss from evolved stars, the 12C/13C ratios in M dwarfs, reflecting those of the past ISM, should be larger than those of the present ISM. In M dwarfs, log 13C/12C plotted against log AC shows a large scatter without clear dependence on the metallicity. This result shows a marked contrast to log 16O/12C (= log AO/AC) plotted against log AC, which shows a rather tight correlation with a larger value at the lower metallicity. Such a contrast can be a natural consequence of 16O and 12C being primary products in stellar nuclear synthesis while 13C is a secondary product, at least partly.