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Abundances of C, N and O as Probes of Mixing in Low-Mass Helium-Core Burning Stars
Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Astronomy and Space Physics. Faculty of Science and Technology, Astronomical observatory. Department of Physics and Astronomy, Theoretical Astrophysics.
2006 (English)In: Convection in Astrophysics, 2006, 66- p.Conference paper (Other (popular scientific, debate etc.))
Abstract [en]

Low-mass stars exhibit signatures of extra-mixing processes that require modeling beyond the standard stellar theory and observational data for stars of different masses and metallicity. Abundances of 12C, 13C, N and O chemical elements in atmospheres of 17 low-mass helium-core burning stars were determined from the high-resolution spectra obtained on the Nordic Optical Telescope with the SOFIN spectrograph. The stars belong to the red clump of the Galaxy and according to the analysis are in the metallicity range of ‑0.28 < [Fe/H] < 0.14 and mass range 1.2 < M /M[Sun]< 2.3. Abundances of carbon were studied using the C[2 ]Swan (0,1) band head at 5635.5 Å. The wavelength interval 7980-8130 Å with strong CN features was analysed in order to determine nitrogen abundances and 12C/13C isotope ratios. The oxygen abundances were determined from the [O I] line at 6300 Å. In comparison to the chemical composition in field dwarfs, the results show that carbon abundance is depleted and [C/H] is lowered in all the star by about 0.2 dex which is in agreement with results for other stars of this type and the theory of the 1st dredge-up. The results of C/N quite closely follow the C/N vs. mass trend predicted by the 1st dredge-up models. The extra-mixing model by Boothroyd & Sackmann (1999, ApJ, 510, 232) does not predict C/N changes to be noticeable at this metallicity and mass as well. Comparing the results with the same theoretical study by Boothroyd & Sackmann (1999) in the 12C/13C, mass plot the stars separate into two groups, one of which follow the trend of 1st dredge-up with 12C/13C ratio being in the range of 20-30, depending of mass. The 12C/13C ratios of the other group of stars is equal to about 15 which show the evidence of extra-mixing. The analysis of a larger sample of Galaxy red clump stars as well as of metal deficient horizontal branch stars is needed for further progress in revealing of extent of mixing in atmospheres of low mass stars.

Place, publisher, year, edition, pages
2006. 66- p.
National Category
Astronomy, Astrophysics and Cosmology
URN: urn:nbn:se:uu:diva-18264ISBN: 1-886733-95-3OAI: oai:DiVA.org:uu-18264DiVA: diva2:46036
Available from: 2006-12-20 Created: 2006-12-20

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