Detalles de publicación

PP 010015

Oxygen isotopic ratios in cool R Coronae Borealis stars

D. A. Garcia-Hernandez(1), D. L. Lambert(2), N. K. Rao(3), K. H. Hinkle(4), K. Eriksson(5)
(1) Instituto de Astrofisica de Canarias, (2) W. J. McDonald Observatory, (3) Indian Institute of Astrophysics, (4) National Optical Astronomy Observatory, (5) Department of Physics and Astronomy, Uppsala University
We investigate the relationship between R Coronae Borealis (RCB) stars and
hydrogen-deficient carbon (HdC) stars by measuring precise 16O/18O ratios for
five cool RCB stars. The 16O/18O ratios are derived by spectrum synthesis from
high-resolution (R=50,000) K-band spectra. Lower limits to the 16O/17O and
14N/15N ratios as well as Na and S abundances (when possible) are also given.
RCB stars in our sample generally display less 18O than HdC stars - the derived
16O/18O ratios range from 3 to 20. The only exception is the RCB star WX CrA,
which seems to be a HdC-like star with 16O/18O=0.3. Our result of a higher
16O/18O ratio for the RCB stars must be accounted for by a theory of the
formation and evolution of HdC and RCB stars. We speculate that a late dredge-up
of products of He-burning, principally 12C and 16O, may convert a 18O-rich HdC
star into a 18O-poor RCB star as the H-deficient star begins its final evolution
from a cool supergiant to the top of the white dwarf cooling track.

Aceptado para publicación en ApJ | Enviado el 2010-03-15 | Proyecto 311586