Carbon and oxygen isotopic ratios in Arcturus and Aldebaran: Constraining the parameters for non convective mixing on the RGB

Abstract

We re-analysed the carbon and oxygen isotopic ratios in the atmospheres of the two bright K giants Arcturus and Aldebaran. Previous determinations of their 16O/18O ratios showed a rough agreement with FDU expectations; however, the estimated 16O/17O and 12C/13C ratios were lower than in the canonical predictions. These anomalies are interpreted as signs of the occurrence of non-convective mixing episodes. We re-investigated this issue in order to verify whether the observed data can be reproduced in this hypothesis and if the well determined properties of the two stars can help us in fixing the uncertain parameters characterizing non-convective mixing and its physical nature. We used high-resolution infrared spectra to derive the 12C/13C and 16O/17O/18O ratios from CO molecular lines near 5 mu. We also reconsidered the determination of the stellar parameters to build the proper atmospheric and evolutionary models. We found that both the C and the O isotopic ratios for the two stars considered actually disagree with pure FDU predictions. This reinforces the idea that non-convective transport episodes occurred in them. By reproducing the observed elemental and isotopic abundances with the help of parametric models of nucleosynthesis and mass circulation, we derived constraints on the properties of non convective mixing. We find that very slow mixing is incapable of explaining the observed data, which require a fast transport. Circulation mechanisms with speeds intermediate between those typical of diffusive and of convective mixing should be at play. We however conclude with a word of caution on the conclusions possible at this stage, as the parameters for the mass transport are rather sensitive to the stellar mass and initial composition.

Accepted for publication in Astron. & Astrophysics

References in corpus (11)

• A grid of MARCS model atmospheres for late-type stars I. Methods and general properties
• Evolution, nucleosynthesis and yields of low mass AGB stars at different metallicities (II): the FRUITY database
• Thermohaline mixing: A physical mechanism governing the photospheric composition of low-mass giants
• Deep Mixing of He-3: Reconciling Big Bang and Stellar Nucleosynthesis
• Fundamental Parameters and Chemical Composition of Arcturus
• Aluminum-, Calcium- And Titanium-Rich Oxide Stardust In Ordinary Chondrite Meteorites
• Can Extra Mixing in RGB and AGB Stars Be Attributed to Magnetic Mechanisms?
• Magnetic Mixing in Red Giant and Asymptotic Giant Branch Stars
• Cool luminous stars: the hybrid nature of their infrared spectra -- Carbon, oxygen, and their isotopic abundances in 23 K - M giant stars
• Abundances in bulge stars from high-resolution, near-IR spectra I. The CNO elements observed during the science verification of CRIRES at VLT
• Close to the Dredge: Precise X-ray C and N Abundances in lambda Andromeda and its Precocious RGB Mixing Problem

Cited by in corpus (25)

• ExoMol molecular line lists XXX: a complete high-accuracy line list for water
• NuGrid stellar data set I. Stellar yields from H to Bi for stars with metallicities Z = 0.02 and Z = 0.01
• The Age and The Mass of The αHerculis Triple-Star System From A MESA Grid of rotating stars with 1.3 <= M/Msun <= 8.0
• Line lists for the A2PI-X2Sigma+ (red) and {B2Sigma+-X2Sigma} (violet) Systems of CN, 13C14N, and 12C15N, and Application to Astronomical Spectra
• The SDSS-III APOGEE Spectral Line List for H-band Spectroscopy
• The APOGEE Data Release 16 Spectral Line List
• The Magnetic Fields at the Surface of Active Single G-K Giants
• On carbon and oxygen isotope ratios in starburst galaxies: New data from NGC253 and Mrk231 and their implications
• ExoMol molecular line lists XIX: high accuracy computed hot line lists for H${}_2$${}^{18}$O and H${}_2$${}^{17}$O
• Carbon and oxygen isotopic ratios for nearby miras
• Chemical evolution of the inner 2 degrees of the Milky Way bulge: [alpha/Fe] trends and metallicity gradients
• Atmospheric parameters and chemical properties of red giants in the CoRoT asteroseismology fields
• Theoretical Estimates of Stellar e-Captures. I. The half-life of 7Be in Evolved Stars
• The puzzle of the CNO isotope ratios in AGB carbon stars
• Oxygen isotopic ratios in intermediate-mass red giants
• The impact of the revised ${}^{17}$O$(p,\alpha {)}^{14}$N reaction rate on ${}^{17}$O stellar abundances and yields
• New Neutron-Capture Measurements in 23 Open Clusters. I. The R-Process
• A Deep Mixing Solution to the Aluminum and Oxygen Isotope Puzzles in Presolar Grains
• Aldebaran b's temperate past uncovered in planet search data
• Analysis of first overtone bands of isotopologues of CO and SiO in stellar spectra
• Chemical composition of giant stars in the open cluster IC 4756
• Isotopic ratios in the red giant component of the recurrent nova T Coronae Borealis
• Exploring masses and CNO surface abundances of red giant stars
• Evidence of Deep Mixing in IRS 7, a Cool Massive Supergiant Member of the Galactic Nuclear Star Cluster
• Three nearby K-giants with planets: Accurate determination of basic parameters, including an analysis of metallicity based on Fe I lines