  We report the discovery of a uniquely large excess of 18O in the
hydrogen-deficient carbon (HdC) star, HD 137613, based on a spectrum of the
first overtone bands of CO at 2.3-2.4 micron in which three strong absorption
bands of 12C18O are clearly present. Bands of 12C16O also are present but no
bands of 13C16O or 12C17O are seen. We estimate an isotopic ratio 16O/18O ~1.
The Solar value of this ratio is ~500. Neither He-core burning nor He-shell
flash burning can produce the isotopic ratios of oxygen and carbon observed in
HD 137613. However, a remarkable similarity exists between the observed
abundances and those found in the outer layers of the broad He-shell of
early-AGB stars, soon after the end of He-core burning. It is not known how the
outer envelope down to the He-shell could be lost but some mechanism of
enhanced mass loss must be involved. HD 137613 may be a post-early-AGB star
with the outer layers of the former He-burning shell as its photosphere.
  The unusual elemental abundances of the HdC stars resemble those of the R
Coronae Borealis (RCB) stars, but HdC stars do not produce clouds of dust that
produce declines in brightness. None of the other RCB or HdC stars observed
shows significant 18O.
