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Issue A&A
Volume 393, Number 2, October II 2002
Page(s) 611 - 615
Section Formation, structure and evolution of stars
DOI http://dx.doi.org/10.1051/0004-6361:20021045



A&A 393, 611-615 (2002)
DOI: 10.1051/0004-6361:20021045

On the use of $^\mathsf{12}$CO/ $^\mathsf{13}$CO as a test of common-envelope evolution

V. S. Dhillon1, S. P. Littlefair1, T. R. Marsh2, M. J. Sarna3 and E. H. Boakes1

1  Department of Physics and Astronomy, University of Sheffield, Sheffield, S3 7RH, UK
    e-mail: vik.dhillon@sheffield.ac.uk
2  Department of Physics and Astronomy, University of Southampton, Highfield, Southampton, SO17 1BJ, UK
    e-mail: trm@astro.soton.ac.uk
3  N. Copernicus Astronomical Center, Polish Academy of Sciences, ul. Bartycka 18, 00-716 Warsaw, Poland
    e-mail: sarna@camk.edu.pl

(Received 7 September 2001 / Accepted 16 July 2002 )

Abstract
We present K-band echelle spectra of the cataclysmic variable SS Cyg and the pre-cataclysmic variable V471 Tau in order to measure the strengths of the 12CO and 13CO bands at 2.3525 and 2.3448  $\mu$m, respectively, and so perform the observational test of the common-envelope model of close binary star evolution proposed by Sarna et al. (1995). Although we find evidence of an absorption feature coincident with the expected wavelength of 13CO in both objects, we attribute it instead to a cluster of neutral atomic absorption features (primarily due to Ti I) possibly arising from star-spots on the surfaces of the rapidly rotating secondary stars in these systems, thereby rendering the test inconclusive. We present a modified observational test of common-envelope evolution, based on the observation of the 13CO bands at 2.3739 and 2.4037  $\mu$m, which is insensitive to spectral contamination by star-spots.


Key words: binaries: spectroscopic -- stars: individual: SS Cyg -- stars: individual: V471 Tau -- novae, cataclysmic variables -- infrared: stars -- nuclear reactions, nucleosynthesis, abundances

Offprint request: V. S. Dhillon, vik.dhillon@shef.ac.uk

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